TD27-05_Road Geometry Links Cross-sections and Headrooms

February 2005

DESIGN MANUAL FOR ROADS AND BRIDGES

VOLUME 6 ROAD GEOMETRYSECTION 1 LINKS

PART 2

TD 27/05

CROSS-SECTIONS AND HEADROOMS

SUMMARY

This Standard sets out the dimensional requirements forthe highway cross-sections for all-purpose andmotorway trunk roads, both at and away fromstructures. It also gives requirements for headroom atstructures.

INSTRUCTIONS FOR USE

1. Remove Contents pages from Volume 6 andinsert new Contents page for Volume 6 datedFebruary 2005.

2. Remove TD 27/96 from Volume 6, Section 1which is superseded by this Standard andarchive as appropriate.

3. Insert TD 27/05 into Volume 5, Section 1.

4. Please archive this sheet as appropriate.

Note: A quarterly index with a full set of VolumeContents Pages is available separately from TheStationery Office Ltd.

TD 27/05

Cross-Sections and Headrooms

Summary: This Standard sets out the dimensional requirements for the highwaycross-sections for all-purpose and motorway trunk roads, both at and awayfrom structures. It also gives requirements for headroom at structures.


THE HIGHWAYS AGENCY

SCOTTISH EXECUTIVE

WELSH ASSEMBLY GOVERNMENTLLYWODRAETH CYNULLIAD CYMRU

THE DEPARTMENT FOR REGIONAL DEVELOPMENTNORTHERN IRELAND

Volume 6 Section 1Part 2 TD 27/05

February 2005

REGISTRATION OF AMENDMENTS

Amend Page No Signature & Date of Amend Page No Signature & Date ofNo incorporation of No incorporation of

amendments amendments

Registration of Amendments


February 2005

REGISTRATION OF AMENDMENTS

Amend Page No Signature & Date of Amend Page No Signature & Date ofNo incorporation of No incorporation of

amendments amendments

Registration of Amendments

VOLUME 6 ROAD GEOMETRYSECTION 1 LINKS

PART 2

TD 27/05

CROSS-SECTIONS AND HEADROOMS

Contents

Chapter

1. Introduction

2. Design Principles

3. Design Process

4. Highway Cross-Sections

5. Highway Cross-Sections at Structures

6. Headrooms at Structures

7. References

8. Enquiries

Annex A Features Commonly Occurring in theHighway Cross-Section

Annex B Rural Motorway Widening, Cross-Sectionand Layout at Physical Restraints


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Chapter 1Introduction

1. INTRODUCTION

1.1 General

1.1.1 This Standard sets out the design principles andfactors that should be considered by DesignOrganisations in selecting highway cross-sections andheadrooms. The process of design is described togetherwith an approach to developing options.

1.1.2 This Standard supersedes TD 27/96. The majorchanges are:

i. the use of a modular system to describe theindividual components of the cross-section;

ii. the acknowledgement that society demandsmeasures to permit better use of existing roads;

iii. further guidance to encourage consideration offuture maintenance operations;

iv. a widening of the road pavement in certaincircumstances for reasons of buildability and toaccommodate future traffic managementlayouts;

v. emphasis on the need to fully consider andpromote facilities for non-motorised road users;

vi. the way in which certain components of thecross-section are measured;

vii. the presentation of information has beenclarified and improved, with new Tables andadditional Figures; and

viii. definitions have been updated and extended:

- guidance associated with reduced widthhardshoulders, central reserve and lanewidths to assist in the widening of ruralmotorways at short obstructions. SeeAnnex B; and

- advice given on the provision of off-sidehardstrips.

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1.2 Scope

1.2.1 This Standard gives details of thecross-sections and headrooms to be used for all-purposeand motorway trunk roads, both at and away fromstructures.

1.2.2 The information covers trunk roads of all types:rural motorways, rural all-purpose roads, urbanmotorways and urban all-purpose roads, together withassociated connector roads.

1.2.3 The cross-section of side roads that are not partof the Overseeing Organisation’s network should beagreed with the relevant Highway Authority. Furtherdetails are given in Chapter 5.

1.2.4 This Standard is not applicable to road tunnels.For guidance see BD 78 (DMRB 2.2.9).

1.2.5 For details of pedestrian, cycle and equestriansubway dimensions see TD 36 (DMRB 6.3.1) andTA 91 (DMRB 5.2.4), for footbridges see BD 29(DMRB 2.2.8), and for agricultural crossings see TA 57(DMRB 6.3) and TA 56 (DMRB 8.2).

1.2.6 This standard does not give mandatoryrequirements for headroom near airports or at powerlines, but Annex A provides details of sources ofinformation.

1.3 Implementation

1.3.1 This Standard must be used forthwith forthe design of all schemes for the construction andimprovement of all-purpose and motorway trunkroads currently being prepared, provided that in theopinion of the Overseeing Organisation, this wouldnot result in any significant additional expense ordelay. The Design Organisation must confirm itsapplication to particular schemes with theOverseeing Organisation.

1.4 Definitions

1.4.1 For the definitions of the general highwayterms used in this Standard, such as “highway types”(trunk roads, motorway and all-purpose roads etc) and

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“components of the highway” (hardshoulders,hardstrips and climbing lanes etc.), see BS 6100:Subsection 2.4.1.

1.4.2 Particular terms used in this Standard aredefined as:

Bridleway: Highway for use on foot or horseback(unless specifically prohibited, cyclists can also use abridleway but are required to give way to other users).

Berm: Any nominally flat area between the back of theverge and the highway boundary at the top of a cuttingor the bottom of an embankment.

Central Reserve: The area that separates thecarriageways of a dual carriageway exclusive of anyhardstrips.

Connector Road: Refer to TD 22 (DMRB 6.2.1).

Cross-section: The assembly of the variouscomponents of the highway between the highwayboundaries, measured at right angles to the line of thehighway. The cross-section includes carriageways,central reserve, separator zones, hardshoulders,hardstrips, verges including any footway, cycle track orbridleway, cutting or embankment slopes and berms.(See Figure 4-1a to Figure 4-4b).

CSRRS (Current Standard for Road RestraintSystems): Please refer to the Overseeing Organisations’current standard for road restraint systems. Note: Wherediagrams within TD 27 show vehicle restraint systems,these are for illustrative purposes only and the CSRRSmust be consulted to determine the appropriateness ofany provision.

Cycle Lane: A lane in the carriageway for use bycyclists.

Cycle Track: A track separate from the maincarriageway for use by cyclists.

Design Organisation: The organisation commissionedto undertake the various phases of scheme preparation.

Designated Lanes: A lane reserved exclusively for useby designated vehicles such as cycles, buses, taxis,large goods vehicles and high occupancy vehicles.

Downstream: That part of the carriageway(s) wherethe traffic is flowing away from the cross-section inquestion.

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Headroom: The minimum distance between the surfaceof the highway cross-section and the deflected structure(including any temporary or permanent attachments)measured at right angles to the surface of thecross-section.

Interchange: Refer to TD 22 (DMRB 6.2.1).

Interchange Link: Refer to TD 22 (DMRB 6.2.1).

Loops: Refer to TD 22 (DMRB 6.2.1).

Mainline: The carriageway carrying the main flow oftraffic (generally traffic passing straight through ajunction or interchange).

Maintained Headroom: The minimum value ofHeadroom that must be preserved at all times.

Margin: EITHER the area between the Paved Widthand an NMU route OR an area between two parallelNMU routes OR an area between an NMU route and aphysical boundary.

New Construction Headroom: The value ofHeadroom for new structures that includes an additionalallowance for future road realignment and resurfacing.

Nearside: Left-hand side of vehicle when viewing aforward moving vehicle from behind, typically thefront-seat passenger side of the vehicle in the UK.

Non-Motorised Users (NMUs): Pedestrians, cyclistsand equestrians including mobility impaired users asdefined in HD 42 (DMRB 5.2.5).

Offside: Right-hand side of vehicle when viewing aforward moving vehicle from behind, typically thedriver’s side of the vehicle in the UK.

Overbridge: A bridge that spans the road underconsideration.

Overseeing Organisation: The Highway Authority forthe road construction or improvement scheme.

Paved Width: A collective term for the surface of theroad cross-section that comprises the carriageway,hardshoulder and hardstrips.

Paved Width Headroom: The value of Headroom overthe Paved Width.

Road Tunnel: Refer to BD 2 (DMRB 1.1).

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Rural Roads: All-purpose roads and motorways thatare generally not subject to a local speed limit. Refer toTA 46 (DMRB 5.1.3).

Separator Zone: An area that separates traffic flows onthe mainline from an adjacent parallel road, e.g. linkroad.

Slip Road: Refer to TD 22 (DMRB 6.2.1).

Standard Headroom: Either Maintained Headroom orNew Construction Headroom, as appropriate.

Structure: Any object with the primary purpose ofbearing loads. This includes bridges, footbridges,retaining walls and sign or signal gantries, but excludesmore frangible items such as deformable vehiclerestraint systems and small span drains.

Structure Free Zone (SFZ): A buffer zone adjacent tothe Paved Width and beneath a Structure that reducesthe risk of errant vehicle impacts by providing anappropriate value of Headroom.

Subway: Underground passageway or tunnel for use bypedestrians, cyclists and sometimes equestrians.

Underbridge: A bridge that carries the road underconsideration.

Urban Roads: Refer to TA 79 (DMRB 5.1.3).

Urban Motorway: A motorway with a speed limit of60 mph or less within a built-up area.

Urban All-Purpose Road (UAP): An all-purpose roadwithin a built-up area, either a single carriageway witha speed limit of 40mph or less or a dual-carriagewaywith a speed limit of 60mph or less.

Upstream: That part of the carriageway(s) wheretraffic is flowing towards the cross-section in question.

Vehicle Restraint System (VRS): Refer to CSRRS.

Verge: Any nominally flat area between the edge of thePaved Width and either the start of an adjacent sideslope or, in the absence of a side slope, the highwayboundary or bridge parapet.

Wide Highway Corridor: Any highway with five ormore lanes in any one direction.

Working Width: Refer to CSRRS.

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1.5 Mandatory Sections

1.5.1 Mandatory sections of this document arecontained in boxes. The Design Organisation mustcomply with these sections or obtain agreement toa Departure from Standard from the OverseeingOrganisation. The remainder of the documentcontains advice and explanation, which iscommended to users for consideration.

1.6 Departures From Standard

1.6.1 In exceptional situations, the OverseeingOrganisation may be prepared to agree to aDeparture from Standard where the standard,including permitted Relaxations, is not realisticallyachievable. Design Organisations faced by suchsituations and wishing to consider pursuing thiscourse must discuss any such option at an earlystage in design with the Overseeing Organisation.Proposals to adopt Departures from Standard mustbe submitted by the Design Organisation to theOverseeing Organisation and formal approvalreceived BEFORE incorporation into a designlayout.

1.7 Relaxations

1.7.1 In difficult circumstances Relaxations maybe introduced at the discretion of the DesignOrganisation, having regard to all relevant localfactors, but only where specifically permitted bythis Standard. Careful consideration must be givento layout options incorporating Relaxations, havingweighed the benefits and any potential disbenefits.Particular attention must be given to the safetyaspects (including operation, maintenance,construction and demolition) and theenvironmental and monetary benefits/disbenefitsthat would result from the use of Relaxations. Theconsideration process must be recorded. Thepreferred option must be compared against optionsthat would meet full Standards.

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Chapter 2Design Principles

ce in the Cross-section

2. DESIGN PRINCIPLES

2.1 General

2.1.1 This chapter describes the principles to befollowed when designing highway cross-sections fornew and improved all-purpose trunk roads andmotorways.

2.1.2 The cross-section is made up from acombination of distinct components that varydepending upon the type of highway and the facilitiesprovided for the various users of the route. Somedecisions relating to the cross-section are made duringproject development, such as the capacity and numberof lanes. Other decisions, such as the type of road, aremade earlier in the process.

2.1.3 This Standard defines and describes thecomponents and presents guidance on details of theirdesign. The basic components are identified separatelyto simplify definition and interpretation as an aid todesign consistency and application. Differentarrangements of the components are to be useddepending on the functional classification of thehighway. The Design Organisation’s role is to decide

Plate 2-1: Sharing Spa

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which of the components to include and the selection ofthe appropriate dimensions.

2.2 Co-ordinated Design

2.2.1 There are many components in a highwayprovided for specific purposes and each involves anumber of interrelated design decisions. Integrating allthese components to satisfy the numerous competingdemands for highway space and functionality requirescarefully balanced decisions. Plate 2-1 provides anillustration to emphasize this point.

2.2.2 Features included in the cross-section canaffect the overall width and their relationship andinteraction is often complex. The preferred locations forfeatures in verges and the central reserve may oftencoincide or overlap and the Design Organisation shouldbe aware of the potential for such conflicts. Generally,there is far more equipment below the surface of vergesand central reserves than is apparent on the surface andsome underground features must be readily accessiblefor routine maintenance.

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2.2.3 Towards the end of the design process, DesignOrganisations are occasionally faced with fittingadditional detailed design features into the availablehighway. Problems can be avoided by ensuring that theapproximate sizes and locations of detailed designfeatures are identified during the very early stages ofthe design so that the required space can be determined.

2.2.4 Design Organisations may need to consider thepossibility of future widening, particularly at structures.See paragraph 5.1.5 for guidance.

2.2.5 Figure 2-1 illustrates the size and extent oftypical features above and below ground that may needto be accommodated in the verge and central reserve ofroads. With the wide range of features that actuallyoccur, details are best designed individually for each

situation. examples the differi

2.2.6 Tblend of tspace balaimpact, coWhere themaking proften comany other the basic dand improharmonio

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Figure 2-1: Typical Features to be

Plate 2-2 and Plate 2-3 show generalof rural and urban road situations to highlightng road environments.

he Design Organisation should ensure that thehe various components within the availablences considerations of safety, environmentalst, buildability, operation and maintenance.re are options for dimensions, the decisionocess should include due consideration of theplex interaction between these factors anddesign constraints. Proper consideration ofesign will help ensure that both new roadsvements to existing highways fitusly into their surroundings.

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Accommodated in the Cross-Section


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Plate 2-2: Typical Rural All Purpose Dual Carriageway Cross-section

Plate 2-3: Typical Urban Cross-section

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2.3 Classification of Highways

2.3.1 Two broad divisions are used in this Standardfor defining the cross-section in association with theenvironment through which the highway passes; namelyRural Roads and Urban Roads. These are furthersubdivided into Motorways and All-Purpose roads witha further category to distinguish between Mainline andConnector roads.

2.4 Variations between Rural and Urban Roads

2.4.1 In urban areas there will usually be less scopefor co-ordinating features than in rural areas, althoughwherever economically and environmentally practicableevery effort should be made to do so. The DesignOrganisation will need to ensure a careful balancebetween the many competing demands.

2.4.2 In urban areas there are likely to be numerousitems of street furniture and underground equipmentwithin the highway cross-section. See TD 9 (DMRB6.1.1) and Transport in the Urban Environment forfurther advice on designing urban single and dualcarriageway roads.

2.4.3 While there may be fewer items ofunderground equipment in rural areas, those that doexist are likely to be high capacity services, whichcould have a bearing on the economical and effectivedelivery of subsequent maintenance and operation ofthe network.

2.5 Network Objectives

2.5.1 The aim is to deliver an economic, accessible,integrated, safe, reliable, efficient and environmentallyacceptable network for all users. This includes the needfor safe, efficient and effective maintenance as well asthe necessity to adapt and improve some highways forthe benefit of non-motorised users. The DesignOrganisation should take these factors into accountthroughout the design process.

2.6 Designated Lanes

2.6.1 With integrated and sustainable transportpolicy now guiding transport planning, the need toconsider and accommodate bus facilities and otherdesignated lanes within the cross-section is likely toincrease. The reallocation of highway space to busesand other designated vehicles can greatly improvejourney times and reliability thereby encouraging modalshift.

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.6.2 In many instances the provision of a designatedne will be achieved through the adaptation of theisting carriageway, especially in urban areas. Thisill often result in a lane being lost for general-purposeaffic. The Overseeing Organisation should thereforee fully satisfied of the net benefits to be derived fromy proposed alterations. It is important to considerese aspects at an early stage in the project appraisal.

2.6.3 The Design Organisation must ensure thatthe proposed cross-section and lane widths areadequate to enable maintenance to be undertakensafely. Care must be taken to ensure that wherecyclists are permitted to use the designated lane,the width is adequate for this purpose.

2.6.4 Any proposal to install a designated laneon a trunk road carriageway is a Departure fromStandard.

.6.5 For further design considerations associatedith designing in an urban environment see TD 9MRB 6.1.1). See Traffic Advisory Leaflets, Local

ransport Notes and Transport in the Urbannvironment for further advice on designing facilitiesr bus lanes and other designated lanes.

.7 Non-Motorised Users

.7.1 It is essential that Design Organisationstegrate facilities for NMUs in the design at an earlyage so that they are not overlooked when allocatingace. To do this effectively, Design Organisations must

e able to understand the highway environment from anMU’s perspective and its relationship to the variousad design components.

2.7.2 During project appraisal involving newconstruction or improvement of an existing road,Design Organisations must determine and makeadequate provision for any NMU requirements.See TA 90 (DMRB 6.3.5), TA 91 (DMRB 5.2.4),HD 42 (DMRB 5.2.5) and IHT Guidelines ForProviding For Journeys On Foot.

.7.3 The Design Organisation’s attention is drawn toe statutory duty to provide proper and sufficientotways for pedestrians and adequate margins fordden horses and driven livestock where it is

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considered necessary, or desirable, for the safety oraccommodation of these road users.

2.8 Persons with Disabilities

2.8.1 Persons with disabilities are better able toparticipate in the community if suitable and accessiblefacilities are available that make it easier for them toreach their desired destinations, especially for those thatdo not drive. Suitable provision is therefore an essentialcomponent of the cross-section because it allowsgreater independence for persons with disabilities.

2.8.2 Legislation prohibits discrimination on thebasis of disability, and the Design Organisation musttake into account any implications of statute whenconsidering the design of highway features.

2.8.3 The required standard of provision forpersons with disabilities must be considered at theearly stages of scheme preparation and the level offacilities must be agreed with the OverseeingOrganisation as part of the reporting procedureoutlined in paragraph 2.7.2 above.

2.8.4 For further advice on designing for the needs ofpersons with disabilities, see Department forTransport guidelines, on Inclusive Mobility.

2.9 Environmental Design

2.9.1 Environmental design features are an integralaspect of the design of any road and many features canhave a significant effect on the required overall widthof highway. The Good Roads Guide (DMRB 10.1 and10.2), HA 67 (DMRB 10.4.1) and DMRB Vol 11describe the approach to be taken.

2.9.2 HA 56 (DMRB 10.1.2 Chapter 12) givesadvice for planting distances between the Paved Widthand trees and shrubs. Design Organisations should beaware that only grass is likely to survive in narrowareas and that a significant width is required to developand maintain trees and shrubs. Thin strips of grass areundesirable as they often fail to prosper and are difficultto maintain. Paragraphs 4.6.6 and 4.6.7 provide furtheradvice on the choice between hard and soft features.

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.3 Existing road corridors may contain significantdiversity interest which may be required to beserved, enhanced or reinstated when roadrovements are being considered.

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Chapter 3Design Process

3. DESIGN PROCESS

3.1 General

3.1.1 For the purposes of developing initial layouts,the Design Organisation should determine theappropriate typical width for the highway cross-sectionand any variation in width required. The type ofhighway and number of lanes needed for a facility isusually determined during the concept stage of projectdevelopment. Figure 3-1 provides a flow chart assimplified guidance on the design process.

3.2 Health and Safety Responsibilities

3.2.1 When selecting the most appropriatecarriageway type, including connector roads, for a newor improved road using TA 46 (DMRB 5.1.3) there is arequirement to consider the future maintenance andoperation of the road. Health and Safety legislation alsorequires that consideration be given at the design stageto the safety of maintenance operations and the safetyof all who may be required to work on or near thehighway in the course of their duties, e.g. emergencyservice personnel. In certain circumstances, whenselecting the cross-section, the Design Organisationmay need to:

i. enhance particular cross-sectional componentsalong a whole route or link;

ii. provide localised widening of standardcross-sections;

iii. select a higher standard carriageway thansuggested on traffic grounds alone by TA 46(DMRB 5.1.3).

3.2.2 Design Organisations must considermaintenance issues on a scheme-by-scheme basisand the selection of standard cross-sections inTA 46 (DMRB 5.1.3) and TD 27 does not obviatethe need for such considerations. The DesignOrganisation must compile a statement of schemespecific maintenance and health and safety issuesensuring that all maintenance activities areconsidered. The Design Organisation must consultwith the Maintaining Organisation when compilingthis statement. The Design Organisation must

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recommend the most appropriate cross-section tothe Overseeing Organisation and must agree thetiming of such recommendations at the outset ofthe scheme. This paragraph does not relieveDesign Organisations of their statutory health andsafety responsibilities.

Range of Choice

.1 The Paved Width of the cross-section variescording to the type of road. Standard dimensions haveen selected on the basis of operational experience in United Kingdom and elsewhere, including theuirements of current and predicted vehicle

nstruction and use.

.2 The widths of traffic lanes, hardshoulders andrdstrips are mandatory for a particular type of road.me flexibility, as described in this Standard, isailable on the width of berms, side slopes, verges andntral reserves.

.3 The required standard of provision and actualsition of features for NMUs should be considered incordance with paragraph 2.7.2.

Visibility

.1 On curved alignments and approaches toctions, it may be necessary to widen thess-section, particularly verges and central reserves,ensure that the layout meets visibility requirements.fer to TD 9 (DMRB 6.1.1).

Features Within the Highway

.1 Annex A provides an indication of the featurest commonly occur within the highway cross-section

a preliminary checklist. Where applicable, Annex Aers to other Standards, Advice Notes and documentst contain further details.

.2 The guidance provided by Annex A emphasizes wide range and often complex interaction oftures that the Design Organisation may have to takeo account when devising a suitable cross-section.

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Chapter 3Design Process

3.5.3 The scheme design should make adequateprovision for the accommodation of roadside equipmentand allow for safe installation and maintenance access.

Allocrosequdev

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Figure 3-1: Cross-Sectio

wances should also be made within thes-section for the future installation of additionalipment as more sophisticated control systems areeloped for the network.

n Design Flow Chart

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Chapter 4Highway Cross-Sections

IONS
4. HIGHWAY CROSS-SECT
4.1 General

4.1.1 This chapter identifies the components of thecross-section and presents guidance on details of theirdesign. It applies to all cross-sections other than thosethrough or across structures for which specificrequirements are given in Chapter 5. Figure 4-1a toFigure 4-4b show sections with detailed dimensions toindicate how the various components should be broughttogether to form the cross-section of different types ofroad.

4.1.2 Numerous changes in the cross-section are notdesirable and a consistent width is to be preferredwhenever practicable along a route.

4.2 Paved Width

4.2.1 The dimensions of the components of thePaved Width must be as given in Figure 4-1a toFigure 4-4b. Any reduction or increase in thesedimensions is a Departure from Standard, with theexception that:

i. 6.0m single carriageway all-purpose roadsare permitted in Scotland and NorthernIreland for design year flows of 5000 AADTor less;

ii. for dual carriageway pinch points, refer toparagraph 4.3.3;

iii. for off-side hardstrips refer to paragraph4.4.3;

iv. for swept paths refer to paragraph 4.3.2.

4.3. Traffic Lane Width

4.3.1 This Standard adopts a single method to definelane widths. Lane widths are measured between thetrafficked side of carriageway edge lines and the centreline of lane lines.

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4.3.2 Traffic lanes must be widened on curvesof low radius to allow for the swept path of longvehicles. See TD 9 (DMRB 6.1.1) and TD 42(DMRB 6.2.6).

4.3.3 TD 9 (DMRB 6.1.1) allows lane widthsnarrower than those given in TD 27 at new dualcarriageways through pinch points. A Departure fromStandard is therefore not required for lane widths thatcomply with TD 9 under these conditions. See TD 9(DMRB 6.1.1).

4.4 Hardstrips

4.4.1 A hardstrip provides a surfaced strip that abutson the carriageway. The key reasons for the provision ofhardstrips include:

i. pavement integrity/stability;

ii. partial, cost-effective provision for stoppedvehicles;

iii. provision of valuable additional width toaccommodate temporary traffic managementlayouts;

iv. snow and water collection;

v. overrun facility for driver error or evasiveaction; and

vi. improved level of service and driver comfort.

4.4.2 The hardstrip also supports edge lines, reducesthe risk of vegetation encroachment over edge lines andallows for the placement of road studs outside vehiclewheel paths, where appropriate.

4.4.3 DMRB 4.2 requires the Design Organisation tocarefully consider the removal of surface water fromoff-side lanes. It is not within the scope of TD 27 topredict the precipitation and drainage requirements of aparticular road and the values of dimension ‘F’ inFigure 4-1a to Figure 4-4b do not include anyallowance for flooded width. Dimension ‘F’ may beincreased to a maximum of 1.00m where appropriate,e.g. when the road falls to the right.

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4.4.4 Hardstrips on urban roads are not normallyprovided due to the associated constraints on land-takeand land costs. Urban roads have lower design speedsand are often more congested than those in rural areas.Generally drivers do not expect rural standards in urbanareas and the restriction of width can assist withencouragement of low speeds, which is of safety benefitdue to the large number of accesses and NMUs,particularly those crossing the road. On urban roads thecarriageway edge treatment will generally includepositive drainage and kerbs, which provides additionaledge restraint and support for raised footways andverges.

4.5 Hardshoulders

4.5.1 The hardshoulder is provided adjacent to thenearside of the carriageway to offer a place to stop inemergencies, clear of mainline traffic. It also providesaccess for emergency vehicles and additional roadspace during temporary traffic management.

4.5.2 Offside hardshoulders are not permitted.

4.6 Central Reserves

4.6.1 Central reserves provide physical separationbetween carriageways thereby providing freedom frominterference from opposing traffic, particularly wherespace is allowed for the construction of a VRS, ifappropriate.

4.6.2 Minimum central reserve widths are givenin Figure 4-1a to Figure 4-4b. A central reservewidth less than the minimum is a Departure fromStandard.

Greater dimensions may be used in circumstanceswhere this would be preferable. The standard widths arebased on the assumption that the road alignment isstraight and level between carriageways and that only aminimal amount of equipment or street furniture needsto be accommodated, either permanently or duringtemporary maintenance activities. The DesignOrganisation should consider whether it is necessary towiden the central reserve in order to:

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i. provide the requisite stopping sight distances inaccordance with TD 9 (DMRB 6.1.1);

ii. accommodate any street furniture, utility ordrainage features and equipment (DMRB 4.2);

iii. meet the requirements of CSRRS for roadrestraint systems;

iv. accommodate any permanent signs requiredwith particular attention to the provision ofadequate working width and set-back for VRSsrelative to the complete sign assembly;

v. accommodate significant difference in levels ofadjacent carriageways;

vi. accommodate temporary traffic managementlayouts for the envisaged maintenance regime;

vii. accommodate matrix signs and signals;

viii. accommodate any parts of structures orcomplete structures;

ix. provide sufficient space for maintenanceoperations;

x. fulfil landscape and environmental objectives;

xi. accommodate NMUs.

4.6.3 The Design Organisation should consider otherfeatures that may have to be accommodated in thecentral reserve, some of which are listed in Annex Aand also the Health and Safety responsibilitieshighlighted in Section 3.2. During project appraisal theDesign Organisation should also ensure that futurenetwork plans for traffic control (e.g. gantries) are takeninto account.

4.6.4 Reference should be made to TD 42 (DMRB6.2.6) for guidance on widening the central reserve atpriority junctions on dual-carriageway all-purposeroads. Away from junctions, crossing places for NMUs,both controlled and uncontrolled, may requiresignificant space, particularly where equestrians andcyclists are expected.

Maintenance Crossovers

4.6.5 TA 92 (DMRB 8.4.6) provides advice on thedesign of central reserve crossovers used duringtemporary traffic management situations, includingadvice for the planning of new roads. BD 78 (DMRB2.2.9) provides requirements on crossovers at tunnels.

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Hardening of Central Reserves

4.6.6 Techniques for reducing maintenance liabilitieswithin central reserves should be considered during thepreparation of new roads and improvements and alsofor major maintenance operations on existing roads toreduce risks to both operatives and other highway users.Such techniques may include hardening or the plantingof low growth species of grass.

4.6.7 When deciding whether to harden centralreserves, Design Organisations should:

i. check the adequacy of the surface waterdrainage system;

ii. make an assessment of environmental factors,such as the landscape character of the settingand location of the road, the environmentalconsequences of weed control and the functionof the central reserve as potential habitat. Theenvironmental database for the route shouldtherefore be consulted;

iii. determine the area to be hardened, based onwhat areas of vegetation may be left uncutwithout affecting visibility or sign conspicuity;

iv. consider the appearance (see paragraph 4.6.9);

v. take account of whole-life costs and safetyconsiderations.

4.6.8 TA 92 (DMRB 8.4.6) gives advice onpavement designs at maintenance crossovers. Awayfrom crossovers, any general hardening of the centralreserve should be designed to be capable ofwithstanding light vehicle over-run and prevent weedgrowth. The Overseeing Organisation should beconsulted for advice on the pavement specification.

4.6.9 Consideration should be given to the provisionof coloured surfacing that contrasts with the maincarriageway where the hardened area may be perceivedas a stopping facility. This is only likely where the VRSset-back is 1.5m or above. The overall width of anycolouring will depend on individual circumstances. Insome situations it may be appropriate to continue thecoloured surface across the whole central reserve, whilein others, for reasons of cost or aesthetics, the widthmay be limited to the traffic side of the VRS.

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Earthworks and Landscaping

4.6.10 It is generally undesirable to provideearthworks and landscaping within the central reserve,as they can be difficult and expensive to maintain.

4.7 Verges

4.7.1 The verge is important from a number ofperspectives, including safety, the environment andwhen considering the initial cost and ongoingmaintenance and operating costs. It can provide aseparate route for NMUs on all-purpose roads and alsooffers an area to accommodate footways and otherdedicated facilities to improve safety and conveniencefor these groups. On motorways, stranded motoristsmay use the verge on foot to reach the emergencytelephones or await the arrival of a rescue vehicle.

4.7.2 Minimum verge widths are given inFigure 4-1a to Figure 4-4b. A verge width less thanthe minimum is a Departure from Standard. Note:Where the Figures denote ‘varies’, the decisionrests with Design Organisations, taking intoaccount the advice in this Standard.

Advice concerning choice of verge width correspondswith that provided for central reserves in Section 4.6.Additional advice solely for verges is given below.

4.7.3 CSRRS provides requirements to ensuresafety if a VRS is struck and deflected near theedge of an embankment slope. DesignOrganisations must comply with CSRRS andwhere necessary, for example on the approach tounderbridges, additional verge width must beprovided.

4.7.4 Motorists often prefer to use the nearside vergein preference to the hardshoulder as a place to stop inthe event of emergencies. This practice can also assistthe passage of emergency vehicles. The provision ofcontinuous nearside VRS, or systems with very fewbreaks, could prejudice this practice. Refer to Section4.11 for advice on increasing a set-back.

4.7.5 For verges on urban roads, in particularmotorways, environmental fencing is becoming aregular feature of the cross-section and the DesignOrganisation should establish the requirements as earlyas practicable.

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4.7.6 Where it is necessary to accommodatecommunications ducting and chambers, aminimum verge width of 2.0m must be provided.

4.7.7 The verge offers an important component inhighway drainage systems, including the storage ofsnow displaced from the carriageway. It offers an areato support utility plant and to house highwayequipment. Congested verges with insufficient room fornecessary roadside components present both safety andengineering difficulties.

4.7.8 The concept of providing wide verges to slowand contain errant vehicles has significant land takeimplications. Research has indicated that only a smallproportion of injury accidents would be avoided ifverges were doubled in width. Consequently, vehicularsafety aspects will not normally be a factor whenchoosing a verge width greater than the minimumwidth, provided visibility requirements are met andspace exists for any VRS that may be required.

4.7.9 Verges should be sufficiently level and freefrom hazards to permit their occasional use by NMUs inthe absence of dedicated facilities. Footways, cycletracks and other NMU facilities are usually providedwithin highways in urban areas, but are less frequent inrural areas.

4.7.10 Provision for NMUs on all-purpose roadsmust be made where a local need has beenidentified and agreed with the OverseeingOrganisation in accordance with TA 90 (DMRB6.3.5), TA 91 (DMRB 5.2.4), HD 42 (DMRB5.2.5) and Environmental Assessment (DMRB11.0).

4.7.11 Where footways are provided, the widthsmust be in accordance with HD 39 (DMRB 7.2.5).

4.8 Berms and Side Slopes

4.8.1 Berm and side slope widths should be chosento suit the local situation. The width of berm willdepend upon:

i. terrain;

ii. environmental design features;

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iii. engineering and geotechnical measures used toaccommodate changes in ground levels;

iv. the need to accommodate various types andwidths of drain and other services in any berm;

v. maintenance requirements.

4.8.2 A degree of flexibility is available to theDesign Organisation when selecting the berm widthalthough a desirable width of 3.0m is recommended.The berm may however provide a reasonable route forNMUs and Design Organisations should consider theirneeds to determine if the chosen width is adequate.

4.8.3 Whenever practicable, side slopes adjacent toemergency roadside telephones should be kept to aminimum angle to assist motorists in waiting at thehighway boundary in the event of an emergency orbreakdown. See TA 73 (DMRB 9.4.2) for furtheradvice on location of emergency telephones.

4.8.4 At all sites where cattle or horses will beexpected to cross the road, any side slope angles willhave an impact on highway safety. Alternative means ofcrossing are described in TA 56 (DMRB 8.2) andTA 57 (DMRB 6.3).

4.9 Wide Highway Corridors

Motorway Lane Provision

4.9.1 Dual 4-lane Motorway remains the maximumstandard of provision in the UK. In exceptionalcircumstances it may be necessary to provide widercarriageways to link closely spaced junctions in order toprovide reasonable lane continuity and sufficientcapacity. Where weaving flows are high it may be moredesirable to provide link roads. For further guidance seeTD 22 (DMRB 6.2.1).

4.9.2 Design Organisations should be aware that forwide carriageways. the size of items such as storagetanks and gantry substructures can be considerable andadequate width should be allowed in verges and centralreserves. Drainage on wide carriageways should also beconsidered at an early stage in the design process withreference to TA 80 (DMRB 4.2.2).

4.9.3 Wide carriageways may also create difficultiesfor maintenance (including provision of a winterservice) and incident management. Also see Section3.2.

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4.9.4 Any proposal for dual 5-lane motorway(D5M) or greater width is a Departure fromStandard.

Auxiliary Lane Provision

4.9.5 Where auxiliary lanes are provided inaccordance with general arrangement layouts givenin TD 22 (DMRB 6.2.1), the width of the auxiliarylane(s) must be equal to the width of the adjacentnearside mainline lane as shown in Figure 4-1a,Figure 4-2a, Figure 4-3a and Figure 4-4a, asappropriate. Any proposal that includes auxiliarylanes, and creates a carriageway of more than fivelanes in one direction is a Departure fromStandard.

4.9.6 The provision of either a hardshoulder orhardstrip adjacent to an auxiliary lane must beconsistent with the provision on the mainline.

4.10 Connector Road Lane Provision

4.10.1 For guidance on determining the requirednumber of lanes, hardshoulder and hardstrip provisionon connector roads, see TD 22 (DMRB 6.2.1).

4.10.2 Where connector roads approach junctions,those dimensions given in the relevant Standards (SeeDMRB 6.2) that prescribe safe and efficient junctiondesigns may take precedence over the cross-sectiondimensions given in this Standard. Traffic movementsat the junction may demand the development ofadditional lanes to provide capacity for separate trafficstreams.

At such connector roads the requirements shown inFigure 4-5 to Figure 4-7 must apply.

4.10.3 Widths of single lane connector roads havebeen determined to allow routine maintenance activitiesto be undertaken. Full resurfacing within such widthsmay not be possible without closing the connector road.Where this is likely to cause significant safety orjourney time disbenefits Design Organisations shouldincrease the width. Consistent with paragraph 4.2.1above, this is a Departure from Standard.

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.10.4 Widths of two lane connector roads have beenetermined to allow all maintenance activities to bendertaken, including full resurfacing. Whereignificant constraints exist, Design Organisations mayonsider a reduction in width via a Departure fromtandard application, taking into account any safety andelay disbenefits of the diversion route if a connectoroad has to be closed. Applications that do not allowoutine maintenance to be carried out in safety whilsteeping the connector road open are unlikely to bepproved.

4.10.5 For slip roads that carry two-way trafficfor some of their length, the width of centralreserve must be consistent with those given inFigure 4-1a, Figure 4-2a, Figure 4-3a andFigure 4-4a. Tight radii will often require greaterwidths to allow for sight lines.

.11 Miscellaneous Features

eparator Zones

.11.1 The widths of separator zones should generallyollow the decision-making process used to determineentral reserve widths discussed in Section 4.6 above.esign Organisations should be aware that minimalidth separator zones could lead to problems due to a

ack of refuge area for occupants of broken downehicles and also for maintenance.

4.11.2. Where traffic on any lane of a parallelroad runs counter to the mainline traffic flow thenthe risks associated with headlight glare must beassessed and the need for mitigation measuresmust be considered.

ethods include:

. designing the alignments of the roads so as toprovide significant level differences;

i. screening fences or earth bunds;

ii. appropriately designed soft planting thatprovides foliage all year round at the correctheights;

v. where the use of a VRS is recommended byCSRRS, it may be practicable to provide asystem that is designed to cut-off glare.

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4.11.3 These items should be considered alongside theadvice given in Section 4.6 above when selecting thewidth required for separator zones.

Chambers and Gullies

4.11.4 Advice on the location of drainage features,including access chambers, is given in DMRB 4.2.Design Organisations should be aware that siting accesschambers and gullies within hardshoulders may affectthe adequacy of temporary traffic management layoutsand may also create additional maintenance liabilities.On all-purpose roads used by cyclists, access chambersand gullies within the hardstrip may also causeproblems.

Maintenance Hardstandings

4.11.5 Consistent with Section 3.2 above, areas ofhardstanding for maintenance activities provide a safetybenefit to the highway and those working on it.Consideration should therefore be given to theirprovision along the route. Hardstandings are mostneeded where only hardstrips are provided and wherehardshoulders are less than 3.0m wide. In the lattercase, this includes most urban motorways.

4.11.6 In all cases, the Design Organisation mustconsult with the Maintaining Organisation, carryout a risk assessment and determine the need forhardstandings.

4.11.7 When selecting locations for anyhardstandings, Design Organisations should follow theadvice given in TA 69 (DMRB 6.3.3) to minimise risk.The width and length of maintenance hardstandingsshould be designed individually for the vehicle typeslikely to use them. For example, at communicationcabinet locations the use will generally be cars or lightvans, but at general purpose locations large goodsvehicles may be expected to deposit equipment.

4.11.8 The frequency of any hardstandings should bedetermined by the Design Organisation, taking intoaccount routine and capital maintenance regimes.Safety benefits will be maximised and cost savings maybe gained by rationalising the locations of equipmentthat requires regular maintenance.

4.11.9 Design Organisations should ensure thathardstandings contrast in appearance with the maincarriageway to dissuade general use. Signing shouldalso be provided to inform the general public of their

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specific purpose. Advice should be sought from theOverseeing Organisation on signing issues. Entry andexit tapers should be minimised to discourage publicuse but without compromising safety. Research is beingundertaken to provide further advice on this matter.

Raised Rib Edgelines

4.11.10 Nearside and Offside edge lines must beraised rib on motorway mainline and connectorroads.

4.11.11 For advice on the use of raised rib roadmarkings on all-purpose roads refer to TrafficSigns Manual Chapter 5.

VRS Set-back

4.11.12 Obstructions immediately adjacent to theedge of the paved carriageway result in driversreducing speed and positioning their vehicles awayfrom the obstruction. The purpose of the set-backis to provide a lateral distance between the VRSand the carriageway which reduces the effect ofthe safety barrier on driver behaviour and drivershyness. Any proposals for departures orrelaxations must consider:

i. In central reserves: the effects on vehiclepositioning within traffic lanes, particularlywhere non-standard lane widths areproposed.

ii. In verges with a hardstrip or hardshoulder:the effects on the ability of occupants ofparked vehicles to leave via the nearsidedoors and the possibility of increased riskdue to parking closer to live traffic.

iii. In verges without a hardstrip orhardshoulder: the effects on vehiclepositioning within traffic lanes, particularlywhere non-standard lane widths areproposed.

iv. In all cases the effects on future temporarytraffic management systems, e.g. a lowset-back, may preclude utilisation of pavedareas for trafficking.

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4.11.13 The set-back is the lateral distancebetween the traffic face of a safety barrier and asappropriate:

i. Nearside: the back of the nearside hardstripor hardshoulder

ii. Nearside: the kerb face for roads without anearside hardstrip or hardshoulder

iii. Offside: the trafficked edge of the edge lineor the kerb face where there is no edge line

The minimum dimensions to be used are given inTable 4-1.

Location Desirable Availableminimum relaxations at

set-back value sites described(mm) in footnotes

In verges with no 1200 Note (i), (ii)adjacent hardstripor hardshoulder

In verges with an 600 (iii)adjacent hardstripor hardshoulder

Central reserves 1200 Note (i), (ii)

Table 4-1: Set-back

Notes

Design Organisations may, where justified,consider Relaxations to set-back as follows:

i. Relaxation to 600mm for roads of speedlimit 50mph or less (including temporarymandatory speed limits).

ii. Relaxation to 1000mm at existing roads withphysical constraints (e.g. a structure) whereit would be difficult to provide the desirablevalue.

iii. Relaxation to 450mm will be permittedwhere it is considered necessary to positionthe VRS away from the edge of an existingembankment in order to provide support tothe foundation.

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4.11.14 On central reserves where there are noobstructions and there is only one double sideddeformable safety barrier between carriageways,the set-back on both sides of the safety barriermust be as stipulated in paragraph 4.11.13 but theymust not be less than the Working Width of thesafety barrier minus the actual width of the safetybarrier.

.11.15 Set-back greater than the minimum valueshould be provided where space allows, particularly ine following circumstances:

At verges for roads where continuous or nearcontinuous VRS is proposed over a long lengthwhere the VRS may prevent a driver frommounting the verge in an emergency.

. Where use of the minimum set-back in centralreserves would result in the Paved Width beingcloser than 600mm to the VRS and wherefuture temporary traffic management andmaintenance regimes would require fullutilisation of the pavement, e.g. on D2AP ruralroads where a minimum set-back for normaloperation (1200mm) could create a problemduring certain temporary traffic managementlayouts if the 1.0m offside hardstrip was to befully trafficked.

i. To achieve a smooth alignment with a parapet.

.12 Rate of Change of Cross-Section Width

.12.1 Notwithstanding the advice in paragraph 4.1.2,ver the length of a route variations in the cross-sectionre likely to be required. Guidance on suitable sourcesf reference to determine the appropriate transitionalrrangement is provided in Table 4-2.

.12.2 Table 4-3 shows the required mainline rate ofhange in width based on a standard 3.65m lane. In allases where Table 4-3 is used, the transition taperhould correspond with the higher design speed of the

o adjoining links under consideration. See TD 22DMRB 6.2.1) for the layout of Merges and Diverges.

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Layout Reference

Mainline Transition in number of lanes TD 9 (DMRB 6.1.1), TD 22 (DMRB 6.2.1),TD 39 (DMRB 6.2.4) and Volume 3 of the Manual

of Contract Documents for Highway Works

Mainline Transition for lane width variations See Table 4-3

Slip Road change in number of lanes TD 39 (DMRB 6.2.4) and Traffic Signs Manual

Transitions from hardshoulder to hardstrip See Figure 4-8 and Figure 4-9

Gain and Loss of Hardstrip on Connector Roads See Figure 4-10with superelevation

Reduction in hardshoulder widths See Annex B. Figure 2 and Figure 3

Change from dual carriageway to single carriageway TD 9 (DMRB 6.1.1) and Traffic Signs Manual

Table 4-2: Transition Reference Table

Design Speed KPH Transition Taper

50 1:25

60 1:30

70 1:35

85 1:45

100 1:50

120 1:55

Table 4-3: Mainline Rate of Change in Width Based on a Standard 3.65m Lane

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4.13 Highway Cross-section Drawings

4.13.1 The following notes should be read inconjunction with Figure 4-1a to Figure 4-4b. Wheresuperscript reference numbers are given in the Figures,these refer to the respective note numbers below:

1. All dimensions are in metres.

2. Verge and central reserve dimensions areminimum values that may need to be increasedto suit particular circumstances (see Section 4.6and 4.7 above). Any value less than theminimum is a Departure from Standard.

3. Carriageway, hardshoulder and nearsidehardstrip dimensions are fixed values; anyalternative proposal is a Departure fromStandard.

4. For guidance on selection of slip roads,interchange links and loops (i.e. MG1A, DG1Aetc.) refer to TD 22 (DMRB 6.2.1).

5. Offside Hardstrips and Verges (See paragraph4.4.3). Where drainage considerations requirean increase in dimension ‘F’ then dimension‘G’ or ‘H’ as appropriate may be reduced by asimilar amount.

6. Refer to paragraph 4.7.6 for details of theminimum verge width required toaccommodate communications equipment.

7. This dimension to be increased by 0.5m whenadjacent to Highway Boundary.

8. Where the Figures denote ‘varies’, the decisionrests with Design Organisations, taking intoaccount the advice in this standard. (Seeparagraph 4.7.2)

9. Measured to the trafficked side of offsideedgeline (rural) or face of offside kerb (urban).

10. Details provided for dual-carriageways areapplicable for both sides of the road.

11. Where noted, some cross-sections may needlocal enhancement by provision of maintenancehardstandings. (See paragraph 4.11.5).

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2. On rural motorways and dual carriageways(including connector roads) Traffic SignsManual Chapter 5 recommends increasinglane lines to 150mm. Such increases may alsobe warranted on roads with lower speed limitswith concrete surfaces.

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ONS AT STRUCTURES

Chapter 5Highway Cross-Sections at Structures

5. HIGHWAY CROSS-SECTI

5.1 General

5.1.1 Cross-sections at structures are detailed inFigure 5-1 to Figure 5-6.

5.1.2 Design Organisations should note that thedefinitions in Section 1.4 may differ from definitionsused elsewhere in DMRB and particularly from those inVolumes 1, 2 and 3.

5.1.3 Variations of Cross-section provision atstructures in close succession should be avoided, exceptwhere necessary to meet the mandatory requirements ofthis or other Standards, e.g. stopping sight distances inTD 9 (DMRB 6.1.1).

5.1.4 The Cross-section of a side road, which isnot a trunk road and is diverted or improved as partof a trunk road scheme must be agreed with therelevant highway, planning and TechnicalApproval Authorities.

5.1.5 Design Organisations should refer to theOverseeing Organisation for advice on the need toconsider future provision at structures. Refer also toBD 2 (DMRB 1.1).

5.1.6 Major roads have the potential to divideexisting habitats and consequently threaten biodiversity.Design Organisations should therefore considermeasures that allow the continued passage of flora andfauna across such roads. These may take the form of‘Green Structures’ that are dedicated to particular floraand fauna, or the inclusion of green components onstructures shared by human users. Examples of thelatter include mammal ledges and soft verges. GreenStructures can also play a significant role in minimisingcommunity severance for NMUs. For further detailsrefer to DMRB 10.4.

5.1.7 Design Organisations should refer to the ‘I’Series of Volume 3 of the Manual of ContractDocuments for Highway Works for the provision ofducts at bridges.

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.2 Non-Motorised User Provision at Structures

5.2.1 The standard of the route for NMUsincluding margins at a structure must be at leastequivalent to that determined for the approaches.

.3 Paved Width Requirements

5.3.1 The paved widths shown in Figure 4-1a toFigure 4-4b must be continued through thestructure.

.4 Side Road Structures

5.4.1 The Cross-section of local roads must beagreed with the relevant highway, planning andTechnical Approval Authorities, based on theadvice contained below in paragraphs 5.4.2 to5.4.4

.4.2 If a structure is required under or over anxisting single lane rural side road of carriageway widthess than 6.0m, the carriageway width of that side roadhould be retained where all the following requirementsre met:

. Traffic flows are not expected to exceed 200vehicles per day.

i. The carriageway width is not less than 3.60mand the lateral width of Cross-section, overwhich the minimum Headroom is provided inaccordance with paragraphs 6.1.3 and 6.3.1, isnot less than 6.60m.

ii. Passing bays, which must be inter-visible, areprovided at each side of the structure.

iv. Stopping Sight Distance to the requirements ofTD 9 (DMRB 6.1.1) is provided.

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5.4.3 For local roads with a carriageway wider than6.0m, there is potential for driver confusion,inappropriate speeds and poor visual appeal beinggenerated by very localised widening. Possiblesolutions to this problem include:

i. providing appropriate transition lengthsbetween the existing and widened sections; and

ii. where provision for possible future widening isthe key criterion – specifying an additionalverge width, such that the road can be broughtup to the required Standard in future, withoutimpinging on structure clearances.

5.4.4 For local roads crossed over by bridges, theCross-section width should also be chosen with dueconsideration to the risk and consequences associatedwith errant vehicle impact. In most cases this can beachieved by complying with the recommendationscontained within this Standard with respect to verges,those within CSRRS with respect to the provision ofVRS and those within BD 60 (DMRB 1.3.5) withrespect to design for vehicle impact.

5.5 Central Reserves

5.5.1 At structures the central reserve widthderived from Chapter 4 must be continued throughor across the structure. However the DesignOrganisation must also consider whether anincrease in width is required for the reasonsdiscussed in Section 4.6.

5.6 Verges

5.6.1 For Overbridges the verge width derivedfrom Chapter 4 must be continued through thestructure. For Underbridges the verge width mustbe as derived from Chapter 4 less any localwidening provided solely for the purpose oflocating a VRS away from the edge of anembankment as described in paragraph 4.7.3.However in either case the Design Organisationmust also consider whether an increase in vergewidth is required for the reasons discussed inSection 4.7.

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Raised Verges and Central Reserves atderbridges

.1 The provision of raised verges and centralerves at underbridges can create a number ofblems. These include:

the restrictions they impose on the availablewidth for running lanes during maintenance;

the need to raise their level when the adjacentcarriageway is overlaid (although it is notalways practicable to raise verges on bridgedecks because of the height of the parapets andparapet upstands); and

providing suitable movement joint andwaterproof details.

.2 These problems however, are usuallytweighed by their many benefits. These include:

improving safety by dissuading the majority ofmoving vehicles from straying dangerouslyclose to the parapet;

if a suitable width is provided, performing thefunction of an NMU route;

accommodation of VRS footings;

forming part of the deck drainage system;

if an appropriate verge width is provided,parked vehicles may benefit, as nearside doorscan be opened for safer egress and the adjacentparapet will be more obvious to driversstepping out from high cab units;

accommodation of services;

. if appropriately detailed, they can be used as astructural component.

5.7.3 For central reserves, the raised width mustbe limited to the minimum required toaccommodate any required NMU route, VRS orservices. The maximum kerb height provided mustbe 75mm.

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5.7.4 For Cross-sections above bridge deckswhere the VRS is a parapet, a raised verge 0.6mminimum width and with a desirable maximumkerb height of 75mm must be provided betweenthe Paved Width and adjacent parapets. Thisapplies to the nearside or offside. The maximumkerb height can be raised to a height not exceeding100mm where it can be shown that significantbenefits result.

This is because dynamic testing has shown that limitingthe height of the kerb upstand to 75mm minimises therisk of an errant vehicle being projected upwards uponimpact. As parapets are designed to restrain vehicles incontact with the adjacent verge surface, minimising thisrisk is critical. A raised verge height of not more than75mm is therefore usually preferable. Where asignificant monetary benefit can be obtained by raisingthe verge slightly, a maximum kerb height of 100mm ishowever acceptable where the adjacent restraint systemis a vehicle parapet. For determining the required vergewidth, also refer to Sections 5.5 and 5.6 which giverequirements that in most cases will necessitate greateroverall verge widths than the minimum dimensionspecified in this paragraph.

5.8 Vehicle Restraint Systems and Parapets

5.8.1 VRS and parapets must be positioned inaccordance with the requirements of CSRRS.

5.9 Divided Structures on Single CarriagewayRoutes

5.9.1 Occasionally it is necessary to provide a singlelane in each direction separated by a central reserve.For instance, certain landmark bridges feature a centralcable stay with a single traffic lane either side. In suchcases single-lane dualling results.

5.9.2 Where single-lane dualling is necessary atdivided structures, the dimensions should bedetermined by following the principles established forsingle lane dualling on all-purpose roads in TD 42(DMRB 6.2.6). An important feature of theCross-section in these situations is that only onethrough lane in each direction is available. There is aneed to allow motorists to pass a stopped vehiclewithout leaving the Paved Width. To achieve this, the

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rough lane in each direction should be 4.0m wide,xclusive of hardstrips and the overall Paved Width ofach carriageway should be at least 6.0m. Seeigure 5-6.

.10 Improving Existing Roads

.10.1 When existing roads are being improved torovide additional lanes or other features the cost

plication of widening a structure may be significant.n these cases, the Overseeing Organisation should beonsulted for advice and it may be practicable toonsider Departures from Standard in accordance withnnex B.

.11 Accommodation Bridges

.11.1 The widths of accommodation bridges shoulde agreed with the Overseeing Organisation afteronsidering the following criteria:

the agreed reasonable needs of the respectiveprivate landowner;

. the size of vehicles, particularly agriculturalvehicles, that may reasonably be expected touse the bridge;

i. maintenance requirements; and

. the needs of NMUs enjoying a legal right ofway.

5.11.2 At the completion of negotiations withlandowners, the agreed provision must be recordedin a formal agreement.

.11.3 For further guidance refer to ‘Provision ofarm Crossings’ published jointly by the Department

or Transport and National Farmers Union, and theReport of the Study Group on Dimensions ofgricultural Bridges and Underpasses’ published byAFF and the Department for Transport.

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Figure 5-6: Cross-Section Components for Dual One Lane All-Purpose Roads at D


TURES

Chapter 6Headrooms at Structures

6. HEADROOMS AT STRUC

6.1. General

6.1.1 Dimensional Standards are given in Table 6-1for New Construction Headroom and MaintainedHeadroom at overbridges and at other structures over ahighway.

6.1.2 For definitions of Headroom, MaintainedHeadroom, New Construction Headroom, Paved WidthHeadroom, Standard Headroom and Structure FreeZone, refer to paragraph 1.4.2.

6.1.3 All new structures must be designed andconstructed to provide a Paved Width Headroomequal to or greater than the New ConstructionHeadroom given in Table 6-1. In addition NewConstruction Headroom must be provided over theextent of the Structure Free Zones in accordancewith paragraph 6.3.1.

6.1.4 Where the Paved Width Headroombeneath an existing structure is reduced as aconsequence of resurfacing, the residual PavedWidth Headroom must not be less than theappropriate Maintained Headroom given inTable 6-1.

6.1.5 Where the Paved Width Headroombeneath an existing structure is proposed to bereduced as a consequence of bridge strengtheningor road widening, the Design Organisation mustconsider all the issues that may influence thechoice of structure headroom, including thosedescribed in paragraphs 6.1.10 and 6.1.11.

6.1.6 The Paved Width Headroom proposed bythe Design Organisation must be subject to theagreement of the Overseeing Organisation. In thecase of existing structures, Design Organisationsmust ensure that any change to the Paved WidthHeadroom as given in paragraphs 6.1.4 and 6.1.5above are documented in the OverseeingOrganisation’s bridge records and planningsystems for the movement of high loads on a route.

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6.1.7 Where a Maintaining Organisation hasidentified an existing structure with Headroom lessthan Maintained Headroom over the Paved Width,the Overseeing Organisation must be advisedimmediately and a risk assessment carried out assoon as is practicable and the structure managed inaccordance with the outcome of that riskassessment.

6.1.8 The Headroom provision at Underbridgesfor trunk roads passing over other authorities’facilities must be agreed with the relevant highway,railway or water authority (road, rail, navigation orriver authority in Scotland). However, where atrunk road passes over another highway, theHeadroom provision must not be less than thecorresponding Standard Headroom given inTable 6-1.

6.1.9 The Standard Headrooms given inTable 6-1 are the minima. Even when Headroom inexcess of these values has been provided, theDesign Organisation may still need to consider theeffects of vehicle collisions on bridgesuperstructures. For new structures the DesignOrganisation must refer to BD 60 (DMRB 1.3.5)for details of design requirements relating tovehicle collision loads on bridge superstructures.

.1.10 Headroom greater than the minimum may beeeded when considering the following issues:

. risk of vehicular impact with thesuperstructure, taking into account records ofvehicle impact and any indicators of previousimpacts on the superstructure;

i. provision for adequate forward visibility insags (see paragraph 6.2.1);

ii. forward visibility to overhead signs andsignals;

v. future implications for maintenance of structureand pavement;

v. whole life costs of structure and pavement;

6/1


ion Headroom (m) Maintained Headroom (m)

0 + S 5.03 + S

7 + S 5.41 + S

N/A 5.411 + S

5 + S 6.181 + S

Headroom at Structures


vi. accommodation of services or apparatus;

vii. compliances with the Design Organisation’shealth and safety responsibilities (seeparagraph 3.2.2);

viii. other site specific issues; and

ix. to provide uniformity of headroom (seeparagraph 6.5.1).

6.1.11 Where it is economical and/or environmentallyacceptable, Headroom greater than the minimum shouldbe provided.

6.1.12 Confirmation of the Paved Width Headroomactually provided based on site measurement alone canbe prone to error as Headroom can seldom be obtaineddirectly by vertical measurement alone. A desk studybased on as-built records is recommended prior toactual on-site measurement, to determine an accuratemethod that will provide the correct perpendicularHeadroom dimension.

Type of structure New Construct

Overbridges 5.3

Footbridges, Sign/Signal Gantries 5.and other structures vulnerable

to vehicular impact

Free Standing Temporary Structures

All Permanent Structures over 6.4High Load Routes2

Where S = Sag Curve Compensation in accordance with Table 6-2

Table 6-1: Standard

1 For Free Standing Temporary Structures and also for a Te2.5.4 of the Traffic Signs Manual, Chapter 8.

2 Not applicable in Northern Ireland.

6/2

6.2 Compensation for Vertical Sag Curvatureand Deflection

6.2.1 Where the road passing under a structureis on a sag curve, the Standard Headrooms inTable 6-1 must be increased in accordance withTable 6-2. The sag radius must be measured alongthe carriageway over a 25m chord.

6.2.2 Allowances must be made for thedeflection of structures. The relevant StandardHeadroom must be provided for the serviceabilitylimit state under the action of the maximum designdeflection. The maximum design deflection mustbe obtained by reference to the relevant loadingstandard.

February 2005

mporary Structure attached to a Permanent Structure refer also to paragraph



Sag Radius (m) Additional ClearanceS (mm)

1000 80

1200 70

1500 55

2000 45

3000 25

6000 15

>6000 Nil

Table 6-2: Sag Curve Compensation

6.3 Structure Free Zone (SFZ)

6.3.1 Errant vehicles may leave the roadpavement leading to a risk of collision withcomponents of the structure. In addition, it maybecome necessary in the future to increase thewidth of the pavement (either permanently ortemporarily) at the expense of the adjacent vergeand central reserve. In order to ensure thatadequate provision is made for thesecircumstances, SFZ must be included beneath allnew structures, by providing the appropriate valueof New Construction Headroom given in Table 6-1over the lesser of the following widths:

i. the full verge width derived from paragraph5.6.1 or central reserve width derived fromparagraph 5.5.1 (deemed to include any sideslopes shallower than 1:4 -vertical:horizontal); and

ii. from the edge of the Paved Width to the faceof any vertical support.

6.3.2 Examples of the Paved Width Headroom andthe SFZ for typical Cross-sections are given inFigure 6-1, Figure 6-2 and Figure 6-3.

6.3.3 Where a Maintaining Organisation hasidentified an existing structure with an SFZ providingless than Maintained Headroom, a risk assessmentshould be carried to determine if measures to safeguard

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e structure are required, e.g. the introduction of aRS.

.3.4 The SFZ defined in paragraph 6.3.1 aboveould be marked on the design and as-built drawings combination with the Paved Width Headroom ande corresponding Maximum Live Load Deflection (asown on Figure 6-1, Figure 6-2 and Figure 6-3) for the

urposes of maintaining accurate bridge records.

6.3.5 Even when an SFZ has been provided, theDesign Organisation may still need to consider theeffects of vehicle collisions. For new structures,the Design Organisation must refer to BD 60(DMRB 1.3.5) for details of design requirementsrelating to vehicle collision loads.

.4 Non-Motorised User Headrooms

6.4.1 Requirements for Headroom at subwaysdedicated to NMUs are contained in TD 36(DMRB 6.3.1).

6.4.2 For structures outside the scope of TD 36(DMRB 6.3.1), Design Organisations must adoptthe Headrooms given in TD 36 (DMRB 6.3.1)where an NMU route is present. Where more thanone Headroom value is quoted in TD 36 (DMRB6.3.1) Design Organisations must adopt the highervalue unless the NMU route is short as defined inTD 36 (DMRB 6.3.1). The initial selection ofNMU Headroom to be provided must be increasedby 300mm where any future overlay of roadpavement could subsequently reduce the adjacentNMU headroom to a value below the requiredminimum.

.5 Uniformity of Headroom Along an Existingoute

.5.1 Where a new overbridge is proposed on anisting route that has overbridges with Headroom

reater than New Construction Headroom,nsideration should be given to providing the same

aved Width Headroom as the existing bridges. Thisniformity of Headroom can lead to a marked reduction the risk of superstructure impacts along that route.he Headroom for new Overbridges on an existing

6/3



route should therefore be increased where this willallow uniformity of Headroom to be provided withoutsignificantly adding to cost. However, considerationshould be given to the vulnerability of footbridges orother lightweight structures that may have lowerHeadrooms than other more robust structures on thesame route.

6.6 Utilities Companies and Other AuthoritiesApparatus

6.6.1 Greater Headroom than that determinedfrom paragraphs 6.1.1 to 6.2.2 and 6.3.1, may berequired by a utility company, or other authority.Any such increase in the Headroom dimensionmust be agreed with the Overseeing Organisation.

6.7 Accommodation Underbridges

6.7.1 The Headroom for accommodationUnderbridges should be selected using the criteria givenin Section 5.11.

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Figure 6-3: Headroom and Structure for a Three Span Structure Crossing a D


Chapter 7References

7. REFERENCES

Department for Transport

Design Manual For Roads and Bridges

BD 2 (DMRB 1.1) Technical Approval ofHighway Structures

BD 60 (DMRB 1.3.5) Design of Highway Bridgesfor Vehicle Collision Loads

BD 29 (DMRB 2.2.8) Design Criteria forFootbridges

BD 78 (DMRB 2.2.9) Design of Road Tunnels

TA 80 (DMRB 4.2.2) Surface Drainage of WideCarriageways

TA 46 (DMRB 5.1.3) Traffic Flow Ranges for Usein the Assessment of NewRural Roads

TA 79 (DMRB 5.1.3) Traffic Capacity of UrbanRoads

TA 91 (DMRB 5.2.4) Provision for Non-MotorisedUsers

HD 42 (DMRB 5.2.5) Non-Motorised User Audits

TA 57 (DRMB 6.3) Roadside Features

TD 9 (DMRB 6.1.1) Highway Link Design

TD 22 (DMRB 6.2.1) Layout of Grade SeparatedJunctions

TD 39 (DMRB 6.2.4) The Design of MajorInterchanges

TD 42 (DMRB 6.2.6) Geometric Design for Major/Minor Priority Junctions

TD 36 (DMRB 6.3.1) Subways for Pedestrians andPedal Cyclists. Layout andDimensions

TA 69 (DMRB 6.3.3) The Location and Layout ofLay-bys

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A 90 (DMRB 6.3.5) The Geometric Design ofPedestrian, Cycle andEquestrian Routes

D 39 (DMRB 7.2.5) Footway Design

A 56 (DMRB 8.2) Hazardous Cattle Crossing:Use of Flashing AmberLamps

A 92 (DMRB 8.4.6) Crossover and ChangeoverDesign

A 73 (DMRB 9.4.2) Motorway EmergencyTelephones

MRB 10.1 and 10.2 The Good Roads Guide

MRB Volume 11 Environmental Assessment

ther Department for Transport Documents

nclusive Mobility (DfT 2003) http://www.dft.gov.uk/tellent/groups/dft_mobility/documents/page/ft_mobility_503282.hcsp

rovision of Farm Crossings (DfT/NFU)

eport of the Study Group on Dimensions ofgricultural Bridges and Underpasses (DfT/MAFF)

he Traffic Signs Manual

anual of Contract Documents for Highway Works

anual of Contract Documents for Highway WorksMCDHW)

ransport Research Laboratory (TRL)

ccidents at Hard Shoulder Discontinuities on Dual-Lane and 3-Lane Motorways - Unpublished ReportR/TT/025/98 (available on request from Overseeingrganisation)

7/1


Chapter 7References

)

The Institution of Highways & Transportation(IHT)

Transport in the Urban Environment (TUE) (IHT 1997

Guidelines for Providing for Journeys on Foot (IHT2000)

Note: The above list does not generally include thosereferences in Annex A.

February 20057/2


February 2005 8/1

8. ENQUIRIES

All technical enquiries or comments on this Standard should be sent in writing as appropriate to:

Chief Highway EngineerThe Highways Agency123 Buckingham Palace RoadLondon G CLARKESW1W 9HA Chief Highway Engineer

Chief Road EngineerScottish ExecutiveVictoria QuayEdinburgh J HOWISONEH6 6QQ Chief Road Engineer

Chief Highway EngineerTransport DirectorateWelsh Assembly GovernmentLlywodraeth Cynulliad CymruCrown Buildings M J A PARKERCardiff Chief Highway EngineerCF10 3NQ Transport Directorate

Director of EngineeringThe Department for Regional DevelopmentRoads ServiceClarence Court10-18 Adelaide Street G W ALLISTERBelfast BT2 8GB Director of Engineering

Chapter 8Enquiries


February 2005

ANNEX A: FEATURES COMMONLY OCCURRING INTHE HIGHWAY CROSS-SECTION

Feature Standard Advice Titleor Guidance

Abnormal load lay-bys No specific reference documents identified

Agricultural/Animal Crossings TA 56 (DMRB 8.2) Hazardous Cattle Crossings: Use of FlashingAmber Lights

TA 57 (DMRB 6.3.3) Roadside Features

Airspace headroom for airstrips International Civil Aviation Specification for the design and equipment fornear roads Organisation Annex 14, aerodromes

Aerodromes

Animal bridges DMRB 10.4

Animal Tunnels DMRB 10.4

Anti-Glare Screens CSRRS

Arrester Beds CSRRS

At-grade crossings TA 68 (DMRB 8.5.1) The Assessment and Design of PedestrianCrossings

TA 15 (DMRB 8.1) Pedestrian Facilities at Traffic Signal Installations


Local Transport Note 2/95 The Design of Pedestrian Crossings

Camera installations TD 17 (DMRB 9.3) Criteria for the Provision of Close CircuitTelevision on Motorways

CCTV Masts BD 83 (DMRB 2.2.11) Design of CCTV Masts

Culverts DMRB 4.2

Cycle facilities TD 36 (DMRB 6.3.1) Subways for Pedestrians and Pedal Cyclists Layoutand Dimensions

Local Transport Note 4/00 Cycling Bibliography

TA 90 (DMRB 6.3.5) The Geometric Design of Pedestrian, Cycle andEquestrian Routes

TA 91 (DMRB 5.2.4) Provision for Non-Motorised Users

Designated lanes including bus lanes, SH 5 (DMRB 8.2) Implementation of Bus Prioritieshigh-occupancy vehicle lanes,non-car lanes Local Transport Note 1/97 Keeping Buses Moving

Traffic Advisory Leaflet 6/01 Bus Priorities

Drainage channels DMRB 4.2

A/1

Annex AFeatures Commonly Occurring in the Highway Cross-Section


February 2005


Drains MCDHW 3.1 Highway Construction Details

HA 37 (DMRB 4.2.4) Hydraulic Design of Road Edge Surface WaterChannels

HA39 (DMRB 4.2.1) Edge of Pavement Details

Emergency telephones TA 73 (DMRB 9.4.2) Motorway Emergency Telephones

Environmental barriers including HA 65 (DMRB 10.5.1) Design Guide for Environmental Barriersscreening fencing and noisefencing/bunds HA 66 (DMRB 10.5.2) Environmental Barriers Technical Requirements

Equestrian facilities TA 90 (DMRB 6.3.5) The Geometric Design of Pedestrian, Cycle andEquestrian Routes


Footbridges BD 29 (DMRB 2.2.8) Design Criteria for Footbridges

Foundations BD 74 (DMRB 2.1.8) Foundations

Geotechnical Monitoring Equipment No specific reference documents identified

Geotextiles No specific reference documents identified

Gullies DMRB 4.2

Hardstandings No specific reference documents identified

High mast lighting columns CSRRS

Highway boundary fencing MCDHW 3.1 Highway Construction Details

Ice prediction and Weather Stations TRMM Trunk Road Maintenance Manual

Kerbing including combined kerb HA 39 (DMRB 4.2) Edge of Pavement Detailsand drainage systems


MCDHW 3.1 Highway Construction Details

Landscaping DMRB Vol. 10 No specific reference documents identified

Lay-bys TA 69 (DMRB 6.3.3) Location and Layout of Lay-bys

Lighting Columns BS 5489 Road Lighting: Guide to General Principles

BD 26 (DMRB 2.2.1) Design of Lighting Columns

TD 30 (DMRB 8.3) Design of Road Lighting for All-Purpose TrunkRoads

BS 5649/EN40 Lighting Columns

TD 34 (DMRB 8.3) Design of Road Lighting for Motorway TrunkRoads

Loop Detectors HD 20 (DMRB 9.3.1) Loop Detectors for Motorways

Maintenance crossovers TA 92 (DMRB 8.4.6) Crossover and Changeover Design

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February 2005


Mobile telephone masts No specific reference documents identified

Motorway Communications DMRB Volume 9, 9a, and 9b Network Traffic Control and Communicationsincluding VMS and infrastructure

MCDHW 3.3 Highway Construction Details

Motorway Markers MCDHW 3.1 Highway Construction Details

Overbridges DMRB Volumes 1 and 2

Overhead Electricity Power Lines Electricity Association Overhead Line ClearancesServices Limited Standard43-8

Pedestrian facilities HD 39 (DMRB 7.2.5) Footway Design

TD 36 (DMRB 6.3.1) Subways for Pedestrians and Pedal Cyclists Layoutand Dimensions

TRL: Application Guide 26 Footways – Design and Maintenance Guide

Local Transport Note 2/86 Shared use by cyclists and pedestrians

Institute of Highways and Guidelines for Providing for Journeys on FootTransportation Guidance

Traffic Advisory Leaflet 3/00 Walking Bibliography

TA 90 (DMRB 6.3.5) The Geometric Design of Pedestrian, Cycle andEquestrian Routes


Pedestrian Guardrails CSRRS

Picnic areas TA 57 (DMRB 6.3.3) Roadside Features

Pipeline structures No specific reference documents identified

Police/Observation Platforms on TA 66 (DMRB 6.3.2) Police Observation Platforms on MotorwaysMotorways

Ponds HA 87 (DMRB 10.0) Environmental Functions

HA 89 (DMRB 10.0) Environmental Elements

Reinforced earth walls BD 70 (DMRB 2.1.5) Strengthened/Reinforced Soils and Other Fills forRetaining Walls and Bridge Abutments

Retaining walls BD 41 (DMRB 2.1.1) Reinforced Clay Brickwork Retaining Walls ofPocket Type and Grouted Cavity Type Construction

BD 42 (DMRB 2.1.2) Design of Embedded Retaining Walls and BridgeAbutments

BD 68 (DMRB 2.1.3) Crib Retaining Walls

BA 68 (DMRB 2.1.4) Crib Retaining Walls

BD 70 (DMRB 2.1.5) Strengthened/Reinforced Soils and Other Fills forRetaining Walls and Bridge Abutments

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February 2005


Rock fences No specific reference documents identified

Sign/Signal Gantries BD 51 (DMRB 2.2.4) Portal and Cantilever Sign/Signal Gantries

Signs TSM Traffic Signs Manual

TSR&GD Traffics Signs Regulations and General Directions

DMRB Volume 8

Sky cradle areas for HV cables National Grid Co. Ltd Design and use of sky cradles at line crossings ofTechnical Doc. TGN [T] 47 motorways, other major roads and railways

Storage tanks/interceptors No specific reference documents identified

Subways TD 36 (DMRB 6.3.1) Subways for Pedestrian and Pedal Cyclists Layoutand Dimensions

Traffic calming Traffic Advisory Leaflet Traffic Calming Bibliography5/00

Traffic Signals TD 50 (DMRB 6.2.3) The Geometric Layout of Signal-ControlledJunctions and Signalised Roundabouts

DMRB 8.1 Traffic Signals and Control Equipment

Local Transport Note 1/98 The Installation of Traffic Signals and AssociatedEquipment

Transmission substations No specific reference documents identified

Tree planting HA 13 (DMRB 5.2) The Planting of Trees and Shrubs

DMRB Volume 10

Underbridges DMRB Volumes 1 and 2

Utility and Statutory Undertakers MCDHW 3.1 Highway Construction DetailsPlant including both above groundapparatus (e.g. cabinets, governors,telegraph poles, etc.) andunderground apparatus (e.g. buriedcables, pipelines, etc.)

Vehicle Restraint Systems CSRRS

VMS Signs TA 60 (DMRB 8.2) The Use of Variable Message Signs on All-Purposeand Motorway Trunk Roads

TD 33 (DMRB 8.2) The Use of Variable Message Signs on All-Purposeand Motorway Trunk Roads

NOTE: Design Organisations must satisfy themselves of the currency of the details contained withinthis table.

MCDHW is The Manual of Contract Documents for Highway Works

A/4



February 2005

ANNEX B: RURAL MOTORWAY WIDENING,CROSS-SECTION AND LAYOUT AT PHYSICALRESTRAINTS

B/1

Annex BRural Motorway Widening, Cross-Section and Layout at Physical Restraints



1. INTRODUCTION

1.1 General

1.1.1 This Annex is based upon guidance developedby the Overseeing Organisations to assist thedevelopment of options at constrained locations for thefirst sections of M25 to be widened. These sections arenow open to traffic and the experience gained has beenincorporated into this document. The results ofcompleted research into the effects of long-standingdiscontinuous hardshoulders and reduced width laneselsewhere on the UK motorway network have also beenincorporated. See TRL unpublished report ‘Accidentsat Hard Shoulder Discontinuities on Dual 2-Lane and3-Lane Motorways’.

1.2 Scope

1.2.1 This Annex gives advice for the preparation ofrural dual four-lane motorway (D4M) improvementschemes that will add or relocate lanes within acarriageway, often within existing highway land andoften at existing structures. Its application is notintended for use on new routes or ‘green field’ sites.The document describes the options for modification ofthe cross-section at physical constraints that occurwhere existing structures cannot readily be widened. Aconstrained location could also occur away fromstructures where the existing highway boundary is closeto the edge of the paved width or a proposed boundaryfence is close to a sensitive location (e.g. Site of SpecialScientific Interest).

1.2.2 Although this Annex has been worded forproposed D4M projects, this advice may also beapplicable for other motorway or dual carriagewayprojects. However in the case of the latter, the needs ofNMUs may preclude the use of narrow verges.

1.3 General Principles

1.3.1 The primary objective is to provide aCross-section that complies with the mandatorysections of TD27. Designs developed using this Annexmay not comply (see Table 1 notes) and in such casesmust be submitted to the Overseeing Organisation forconsideration as Departures from Standard.

1.3notStasigwocon

1.3invpriparpraRehasdo mo

1.3struriskmaassimp

1.3effOrglegThcon

1.3perser

1.3likeSta

B/2

.2 Small changes in cost or other small effects are sufficient justification for Departures fromndards. Design Organisations must demonstrate thatnificant and disproportionate costs or other effectsuld result from adoption of full standards, beforesidering non-standard designs.

.3 Making the best use of the available widtholves firstly using all spare space. The secondnciple is to maintain the width of running lanes,ticularly those carrying heavy vehicles, as far ascticable because these are in use all the time.search and experience, both from the UK and abroad, shown that short discontinuities in the hardshouldernot materially affect the good safety record oftorways.

.4 Where traffic is moved closer to existingctures, the Design Organisation must consider the of collision with the structure. Reference must be

de to BD 48 (DMRB 3.4.7) for guidance onessing the susceptibility of the supports to vehicleact.

.5 Narrow Cross-sections may affect the viability,iciency or safety of maintenance operations. Designanisations, in accordance with Health and Safety

islation, must consider such effects in all designs.e Maintaining Organisation must always besulted.

.6 Narrow Cross-sections may affect theformance of the emergency services. The emergencyvices must always be consulted.

.7 The Design Organisation must determine thely risks and report its findings with Departure fromndard submissions.

February 2005


ONS AT CONSTRAINTS


2. DEVELOPMENT OF OPTI

2.1 Application of Departures

2.1.1 The priority order in which departures andrelaxations must be applied when apportioning theavailable space to the various components is given inTable 1, which should be read in conjunction withFigure 1. The hierarchy should be applied in sequence,with the appropriate adjustment made to the relatedcross-sectional element whenever practicable, beforeproceeding to the next level.

2.1.2 The following paragraphs deal with theprovision and width of components, the choice of VRSsand the set-back to them, hardshoulder width anddiscontinuities, emergency access routes, and trafficlane widths.

2.2 Verge and Central Reserve (1 and 2 inTable 1)

2.2.1 Design Organisations should consider reducingthe width of verges and the central reserve to theminimum required to accommodate equipment (seeSections 4.6 and 4.7 of the main document).

2.2.2 At Underbridges, the Design Organisationshould be aware of paragraph 5.7.4 in the maindocument with respect to raised verges adjacent to aparapet.

2.3 Clearance to Structures (3 in Table 1)

2.3.1 Limiting the space devoted to VRSs may beachieved by the use of types that maximise the spacefor traffic. Further space savings can be achieved by theuse of smooth, non-snagging concrete faces to existingpiers, abutments and retaining walls, in conjunctionwith flush-fitted VRSs on both approach and departingends of the structure face. The structure must be able toresist the appropriate impact loading if it is to performthe dual function of a structure and a VRS. Even whereVRSs are provided, it may still be necessary forstructures to resist residual impact loading. New pointsof impact loading from any new access routes behindpiers should also be considered.

2.3.2 Emergency access routes are contained withinthe Paved Width defined in the main document.

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.3.3 Headroom requirements are given in Section 6f the main document.

.4 Set-back to Vehicle Restraint Systems4 to 11 in Table 1)

.4.1 Desirable minimum set-back values are given Section 4.11 of the main document.

.4.2 At constraints the set-back to the hardshoulderould be reduced to zero and to a traffic lane to 1.0m.he set-back on the offside of a traffic lane from aeformable VRS could be reduced to 0.80m. RigidRSs are more noticeable to drivers and consequently is recommended that set-backs to them are not lessan 1.0m. The Working Width behind the VRS allows

or deflection of the barrier on impact and Departuresrom Standard on working width are not usuallyermitted.

.5 Motorway Hard Shoulder Provision4 to 6 in Table 1)

.5.1 The standard rural hardshoulder width of

.30m is desirable. Its function is described in Section

.5 of the main document.

.5.2 Hard shoulder width may be reduced to 3.0mithout significantly reducing effectiveness and safety

or breakdown and emergency use. Widths of less than.0m should be regarded as discontinuities of theardshoulder and therefore not for public use.

.5.3 Where the Design Organisation requires theardshoulder to be discontinued, the space should besed to provide an emergency access route. Any localiscontinuity of the hardshoulder should be as short asracticable and marked as shown in Figure 2. Inddition to markings, appropriate signs must berovided advising of loss of hardshoulders. Seearagraph 2.13.4 below.

.5.4 Between local discontinuities the minimumngth of hardshoulder for public use (3.0m minimumidth) should be 100m between the tips of taperarkings to allow for safe stopping and rejoining.here widths of greater than 3.0m are provided

etween two discontinuities, but the length is less than100m, the hatching must be continued.

B/3



2.5.5 The retention of a hardshoulder on the 300mbefore a diverge is less important than at other pointsbecause drivers of vehicles with mechanical difficultiescan usually manage to reach the off-slip. Conversely, adiscontinuity of the hardshoulder immediately after amerge should be avoided because drivers who havedifficulty merging tend to overrun the hardshoulder.Nearside lane-gain junctions do not normally presentthis risk.

2.6 Motorway Emergency Access (7 to 11 inTable 1)

2.6.1 Emergency services make use of thehardshoulder to reach incidents. The level of severity ofaccidents often depends on the time taken foremergency services to reach an incident. Atdiscontinuities of the hardshoulder, emergency servicescan make use of widths of 2.50m or less (absoluteminimum 1.0m) for access purposes, provided Lane 1 isstandard width. This is particularly desirable where thealternative route would be time consuming, such as atviaducts. Any emergency access width adjacent to theleft-hand lane should be hatched and signed as adiscontinuous hardshoulder to discourage public use.

2.6.2 Bridges with open side-spans may permitconstruction of a continuous access roadway foremergency vehicles behind the pier at a hardshoulderdiscontinuity. Figure 3 shows a typical layout.

2.6.3 Where it is proposed to create discontinuitiesof the hardshoulder that would cause significantdifficulties for the emergency services in reachingincidents, the Design Organisation should consider theprovision of alternative access roadways separate fromthe motorway. These might start from interchanges,maintenance compounds, or special accesses from localroads or other access points at the motorway boundary.It is highly desirable that the presence and destinationof access roadways is not readily apparent to the publicto minimise the possibility of unauthorised use. Signs,markings and often physical barriers will be necessary.

2.6.4 The Design Organisation must consult with theemergency services in writing on the access provisionfor rural motorway schemes with hardshoulders lessthan 3.0m in width. This must be included in a sitespecific risk assessment undertaken by the DesignOrganisation that takes into account local factors, e.g.some sites may have higher risks due to the length ofalternative routes and/or proximity of major venues,hospitals, airports or major industrial works.

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.6.5 For layouts such as those shown in Figure 3,he risk of impact with bridge piers may be higher thanhe layout given in Figure 2. In addition, the risk ofehicles being launched from the ramped-ends of VRSss higher. Therefore it is recommended that Designrganisations consult CSRRS with a view to

onsidering the use of crash cushions for such layouts. warning bollard with reflective materials should alsoe provided. Also refer to paragraph 1.3.4 for guidancen the requirements to check bridge piers for impact.

.7 Width of Traffic Lanes (10 to 11 in Table 1)

.7.1 The standard lane widths in TD 27 for a fourane rural motorway are shown at A1 in Figure 1. Theane dimensions are measured between the traffickedide of carriageway edge lines and the centre line ofane lines and this convention is followed in this Annex.esign Organisations should, however, take care to

tate the points on the lane markings that anyimensions are measured between when specifyingarrower lanes.

.7.2 Traffic lane widths less than standard may beonsidered for lanes 1, 2, 3 and 4. Lane 1 may beeduced to 3.60m, lane 2 to 3.50m, lane 3 to 3.35m, andane 4 to 3.35m. Section A2 in Figure 1 shows theseidths. The pavement construction should be extended

nto the set-back area on the offside where the width ofane 4 is reduced. However, as described in paragraph.11.15 of the main document, extension of theavement within a 600mm zone from the VRS wouldot normally be warranted. It is recommended that theentral reserve is hardened as described in Section 4.6f the main document so that accidental overrun isccommodated safely.

.7.3 Where the space available for traffic lanes isess than the standard section, but more than in Section2 in Figure 1, the additional space should be allocated

irst to lane 1, then to offside lanes, up to the standardidth of section in Section A1 in Figure 1.

.7.4 Exceptionally, lane widths less than in Section2 in Figure 1 may be necessary over short lengths and

omplementary signing is likely to be required in suchases. Such signing will require special authorisation.peed limit and/or width prohibition traffic orders maye required.

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2.8 Transitions Between Sections of DifferentWidth

2.8.1 The length of transition from one Cross-sectionto another should be sufficient for drivers to follownaturally the alignment of the lane lines and edge linesahead and to negotiate and adjust position relative tovehicles in adjacent lanes. Changes in direction of roadmarkings should be smooth and curved. Table 4-2 of themain document provides minimum requirements but,because variations of standards on motorways are rare,it is recommended that taper angles of 1:100 orshallower are adopted.

2.9 Length

2.9.1 Adoption of the options contained within thisAnnex for modifying the hardshoulder and carriagewayCross-section and layout at physical constraints is onlyconsidered appropriate at short obstructions (i.e. lessthan 100m in length, exclusive of tapers). Approval forlonger sections (i.e. greater than 100m) will not beconsidered unless there is very strong justification interms of safety, reliability, efficiency and environmentalimpact.

2.9.2 For schemes where more than one discontinuityis proposed, Design Organisations should be aware thatnumerous discontinuities can:

i. increase response times for emergency vehicleswhen queuing traffic is present;

ii. increase risk to the travelling public;

iii. affect the safety of maintenance; and

iv. increase delays during maintenance operationsand incident management as sufficient widthmay not be available to provide the requirednumber of traffic lanes.

[Note: The adverse effects described above will beaggravated where a discontinuity coincides withreduced lane widths.]

2.9.3 Driving on narrow lanes for long distancesrequires considerable levels of concentration, as there isvery little margin for error when steering a vehicle,particularly where numbers of Large Goods Vehiclesare high. Driving for long distances through this type oflayout would increase driver stress, possibly resulting injudgement errors and an increase in the risk ofaccidents. It is not envisaged that reduced lane widthswould be continued over long lengths.

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.10 Emergency Telephones at Discontinuities

.10.1 Where currently installed on a route,mergency telephones should be provided at either sidef discontinuities, so that drivers in difficulty will bencouraged to stop before the discontinuity, and allrivers seeking assistance can walk to a telephoneithout crossing the discontinuity. Emergencylephones should be located in positions where it is

afe for both a vehicle to stop and subsequently rejoine carriageway and for pedestrians, including thoseith mobility impairments, to travel between the phone

nd vehicle. Emergency telephones should be locatedn lengths with full width hardshoulders in preference lengths without hardshoulders, or with emergency

ccess routes.

.10.2 In situations where verge width is very limitedver a long length, such as at retaining walls,onsideration should be given to local verge wideningt the telephone site, reached through an overlap in theRS where these are required, to improve the safety ofose using the telephone.

.10.3 It may be feasible to route pedestrians throughide spans if the verge is hardened and signing isrovided.

.11 Cross-section Departures in Combinationith Other Relaxations

.11.1 In many cases, Relaxations permitted by TD 9DMRB 6.1.1), in visibility, horizontal curvature, andertical curvature will be acceptable in combinationith cross-section departures. However, these aspects,

s with any other local features at a constrained locationhould be considered in the development of options andeported in any submission for Departures fromtandard.

.12 Maintenance Implications

.12.1 Reductions of the surfaced width can bexpected to have implications for future maintenancend the Maintaining Organisation must be consulted onis aspect. Checks should be made that layouts are

apable of safe and satisfactory operation duringlosures by considering the necessary trafficanagement measures, including temporary signing.onsideration should be given to ploughed snow

torage, salting routes and diversion routes.aintenance activities also require access to structures

nd ancillary items such as drainage, signs, lighting,ignalling equipment, planting and mown areas.

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2.12.2 Where the hardshoulder is less than 3.0mmaintenance hardstandings must be considered inaccordance with the guidance provided by paragraph4.11.5 of the main document.

2.13 Mitigation

2.13.1 As with any non-standard situation, DesignOrganisations must consider suitable mitigationmeasures to reduce any identified risks.

2.13.2 Signing to warn drivers of width reductions isdiscussed at paragraph 2.7.4 above.

2.13.3 Typical road marking layouts for locationswhere the width of hardshoulder would be less than3.0m are shown in Figures 2 and 3.

2.13.4 Statutory Requirements for signing andmarking are contained in the Traffic Signs Regulationsand General Directions, which in many cases willindicate hatched markings to diagram 1040.5, inconjunction with a sign to diagram 820.1. Where breaksin the hardshoulder are intermittent, a single signadvising of the total length of discontinuoushardshoulder may be preferable to signing each breakseparately. Variants of diagram 820.1 have been used,although this case requires signs authorisation by theOverseeing Organisation.

2.13.5 Chapter 4 of the Traffic Signs Manual givesadvice about the siting of warning signs. Diagram 820.1is considered to be a warning sign. The Traffic SignsManual gives advice about the distance betweenwarning signs and the hazard. The hazard must be takento be the first physical incursion into the normal 3.30mhardshoulder.

2.13.6 Recent advances in technology allow networkoperators to be alerted to vehicles stopped on thecarriageway. This could be via use of inductive loops,CCTV or intelligent video systems. Where risks areconsidered to be high (e.g. where hardshoulderdiscontinuities are long) the Design Organisationshould consider such mitigation measures.

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Priority Comments Left-hand Hard Running Right-Hand OverallOrder Set-back Shoulder or Lane Widths Set-back Width

(see Emergency Between “F”Note 1) Access Width Points in Fig.1

1 (Paragraph 2.2) Reduce verge widths

2 (Paragraph 2.2) Reduce central reserve width

3 (Paragraph 2.3) Limit space devoted to VRSs (See Note 2)

4 Minimum standard section 0.60m to back(Figure 1; A1) of 1.20m 19.80m

hardshoulder

5 Reduce: ZeroSet-back adjacent to the The minimum 3.30m

hardshoulder to a minimum set-back of hardshoulderof zero, and adjacent to a 1.0m to the 18.80m

traffic lane to a minimum of nearside0.80m (See Note 3) traffic lane is

included6 Reduce: within the

Hardshoulder width, to a emergencyminimum of 3.0m access width 3.0m 18.50m

hardshoulder 14.70mstandard lane

7 Provide: widths2.50m emergency access 2.50m

route for emergency vehicles emergencyonly access 18.00m

(hatched &signed)

8 Provide: 0.80m2.0m emergency access 2.0m (See Note 3)

route for emergency vehicles emergencyonly access 17.50m

Zero (hatched &signed)

The minimum9 Reduce: set-back of

Emergency access route to 1.0m to the 16.50m1.0m nearside

traffic lane is10 Reduce included 14.40m

Lane 4 to 3.55m within the 1.0m reduced width 16.20mLane 3 to 3.60m emergency emergency of lane 4Lane 2 to 3.60m access width access

(hatched &11 Reduce signed) 13.80m

Lane 4 to 3.35mLane 3 to 3.35m Figure 1; A2- 15.60mLane 2 to 3.50m reduced widthLane 1 to 3.60m lanes 2, 3 & 4(Figure 1; A2)

Note:1 For schemes within the Scope defined in paragraphs 1.2.1 and 1.2.2 of this Annex, it is permitted to adopt steps 1 to 6 as

Relaxations (with the exception of Working Width as described in paragraph 2.4.2). Steps 7 to 11 are Departures fromStandard.

2 Refer to paragraph 2.4.2 of this Annex for advice on allowable relaxations in set-back.3 For double sided deformable barriers this dimension must be checked to ensure that the deflected system does not

encroach into the opposite live traffic lane. Also for rigid VRSs the 0.80m set-back must be increased to 1.0m.4 For interpolation between steps refer to paragraph 2.7.3.

Table 1: Priority Order For Cross-section Reductions At Physical Constraints

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Figure 1 - Cross-section Examples At Physical Constraints

19.80m

0.60m 3.30m 1.20m

0.20m 0.10m 0.10m 0.10m 0.20m

3.70m 3.65m3.70m3.65m

hardshoulder Lane 4Lane 3Lane 2Lane 1

F F

0.80m*

0.20m

F

18.50m

0.20m 0.10m 0.10m 0.10m

3.70m 3.65m3.70m3.65m

hardshoulder Lane 4Lane 3Lane 2Lane 1

F

3.00m

Note: Refer to para. 2.7.2 of this Annex B for details on edge treatment.

0.20m

0.80m*

15.60m

1.00m

0.20m 0.10m 0.10m 0.10m

3.35m 3.35m3.50m3.60m

Lane 4Lane 3Lane 2Lane 1

FF

Note: Refer to para. 2.7.2 of this Annex B for details on edge treatment.

A1 – STANDARD 4 LANE SECTION No.4 in Table 1

REDUCED WIDTH HARD SHOULDER & SET BACK No.6 in Table 1

A2 – REDUCED WIDTH LANES AND SET-BACK AND MINIMUM EMERGENCY ACCESS

No.11 in Table 1

Note:

F Face of physical constraint. Note that for parapets paragraph 2.2.2 of this Annex refers.

* 1.00m minimum to rigid VRSs.

Refer to paragraph 4.13.1(12) of the main document with regard to lane line widths.

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Figure 2 - Layout at a Discontinuity of the Hardshoulder

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Figure 3 - Access Roadway for Emergency Vehicles

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