Infrastructure Risk (IRR)Manual - NZ Transport Agency · Infrastructure Risk Rating Manual 2 2 Infrastructure Risk Rating Coding To assess risk and determine an Infrastructure Risk

InfrastructureRiskRating(IRR)Manual

PreparedfortheNewZealandTransportAgency

July2016

Infrastructure Risk Rating Manual

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DevelopmentStatusoftheIRRModel

The Infrastructure Risk Rating (IRR) model and methodology presented in this document has been

developed, trialled and refined in a number of New Zealand locations. The working group tasked

with developing the model are satisfied that the results being generated by the IRR model are

intuitive and fit for purpose. However, it should be noted that further development and revision may

occur in the future.

Disclaimer

This document has been prepared for the benefit of the NZ Transport Agency. No liability is accepted

by the company’s or persons who have prepared this document with respect to its use by any other

person.

This disclaimer shall apply notwithstanding that this document may be made available to other

persons for an application for permission or approval to fulfil a legal requirement.

Acknowledgments

The IRR model has been developed as part of a collaborative process. The working group tasked with

the development and testing of the model are:

Colin Brodie & Fergus Tate, New Zealand Transport Agency, Wellington Paul Durdin & Haris Zia, Abley Transportation, Christchurch Shane Turner, MWH, Christchurch Gina Waibl, Gina Waibl Consulting, Christchurch


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Contents

Development Status of the IRR Model .................................................................................................... i

Disclaimer................................................................................................................................................. i

Acknowledgments .................................................................................................................................... i

1 Introduction .................................................................................................................................... 1

1.1 Infrastructure Risk Rating Features ........................................................................................ 1

2 Infrastructure Risk Rating Coding ................................................................................................... 2

2.1 Definition of a Divided Road ................................................................................................... 2

2.2 Identifying Sections for Coding ............................................................................................... 3

2.3 Data Fields ............................................................................................................................... 4

2.4 Road Stereotype ..................................................................................................................... 6

2.5 Alignment ................................................................................................................................ 6

2.6 Carriageway Width .................................................................................................................. 7

2.7 Roadside Hazards .................................................................................................................... 8

2.8 Land Use ................................................................................................................................ 11

2.9 Intersection and Access Density ........................................................................................... 12

2.10 Traffic Volume ....................................................................................................................... 13

3 IRR Model ...................................................................................................................................... 14

4 Automated Process Overview ....................................................................................................... 18

4.1 Geospatial Process for Creating Homogenous Sections ....................................................... 18

4.2 IRR Attributes Coding Automation ........................................................................................ 19

4.2.1 Road Stereotype Coding Automation ........................................................................... 19

4.2.2 Alignment Coding Automation ..................................................................................... 19

4.2.3 Carriageway Width Coding Automation ....................................................................... 19

4.2.4 Roadside Hazard Risk Coding Automation .................................................................... 19

4.2.5 Land Use Coding Automation ....................................................................................... 20

4.2.6 Intersection Density Coding Automation ...................................................................... 20

4.2.7 Access Density Coding Automation .............................................................................. 20

4.2.8 Traffic Volume Coding Automation .............................................................................. 21

Appendix A: Roadside Hazard Rating Examples ................................................................................... 22


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1 Introduction Infrastructure Risk Rating (IRR) is a road assessment methodology designed to assess road safety

risk, primarily as an input to the speed management process. The road safety risk is assessed by

coding each road and roadside feature that feeds into the IRR model so that a risk rating can be

determined.

This Appendix describes the IRR model and the methods available for applying it. The Speed

Management Guide provides information on how IRR is used.

1.1 InfrastructureRiskRatingFeatures In IRR, eight key features have been identified that impact on safety risk. These are:

Road stereotype

Alignment

Carriageway width

Roadside hazards

Land use

Intersection density

Access density

Traffic volume

Section 2 of this Appendix provides guidance for coders to identify sections for coding and to select

the appropriate category for each feature rated in IRR. Section 3 includes the risk scores associated

with each IRR feature and the form of the IRR model. There is also a separate IRR spreadsheet tool

available which can be used to calculate the IRR Score.


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2 InfrastructureRiskRatingCoding To assess risk and determine an Infrastructure Risk Rating (IRR) score, the IRR features must be

assessed and coded by assigning each feature a value based on the available categories (as shown in

Sections 2.4 to 2.10). However, before coding can begin, road sections need to be identified for

coding as outlined in Sections 2.1 and 2.2 below; and section location and description data entered,

as shown in Section 2.3. Coding and sectioning can either be done manually or using an automated

process (see Section 4).

Various media and data sources will be available to the coder. Aerial imagery is useful for gaining an

overview of the section to be coded and can be used to code features such as alignment. Existing

data sources, such as Road Asset Maintenance Management (RAMM) databases, are useful for

coding traffic volume and can be used to code other features such as carriageway width. However,

for some features, particularly roadside hazards, a street level view is required. If high speed video is

available this is ideal, but otherwise coding of these features can be done during a site visit. Coding

can also be done using still images, such as Google Street View, but this will likely be slower and less

accurate as it is more difficult to get a complete picture of the road corridor.

As with other risk rating methodologies, divided and undivided carriageways are coded differently.

Divided carriageways are coded in both directions, while undivided carriageways are coded once,

with both sides of the road coded while viewing the road travelling in one direction.

An IRR spreadsheet tool has been developed as an accompaniment to this coding manual, and can

be used for the input of coding data and calculation of the IRR Score.

2.1 DefinitionofaDividedRoad For the purposes of coding, a road is treated as divided if there is a physical feature separating

opposing traffic flows and preventing vehicle movements across the median. A physical separating

feature is any kind of raised median, such as a kerb island, or safety barrier. There may be gaps

present in the median at intersections.

Divided roads include traversable and non‐traversable medians. A divided traversable median may

not stop an out of control vehicle from crossing the median but is sufficient to deter or prevent

general vehicle turning movements across the median.

If there are flexi‐posts present in the median, the road would be coded as divided if the posts are

spaced closely enough to prevent vehicle movements across the median.

Roads with features such as a flush median, centreline rumbles strips or wide centrelines do not

prevent vehicle movements across them and as such should be coded as undivided.

Short lengths of divided road (less than 1km), such as on the approach to an intersection are ignored

and treated as part of the undivided road section and vice versa for divided roads with short sections

of undivided road.


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2.2 IdentifyingSectionsforCoding To simplify and expedite coding, road sections are selected where there is little variation in IRR

features. These are referred to as homogenous sections. One way to think of these is that, broadly,

homogenous sections are those where the speed limit would be the same.

To select homogenous sections prior to coding:

1. Aim for sections to be around 5km in length, though sections between 3km and 7km in length

are acceptable. Shorter lengths (around 1km) can be used where necessary but should be

avoided where possible. These shorter lengths are typically only expected where there has been

a significant change in road stereotype or land use, intersection density or access density.

2. Consider land use and intersection and access density and make section breaks where land use

changes or intersection and access density change significantly. If the change is over a short

length (<1km) then consider how significant the change is and whether a section break is

required. If there is a speed limit change in the vicinity of the land use change (within 500m)

then the section should start/end at the speed limit change. Where multiple speed limits are

present, create section boundaries at the urban/rural boundary (where urban and rural are

defined by land use as shown in Section 3). Maps and aerial photography can be used to assist

with this prior to coding although a street level view is recommended to define the section

boundaries.

3. Road stereotype must be unchanged over the length, except for short changes <1km in length

such as at intersections, turning bays, slow vehicle bays, short passing lanes etc. Use maps and

aerial photography prior to coding if desired, and refine using a street level view as not all road

stereotype changes will be identified from maps.

4. For rural roads use aerial imagery to identify changes in road alignment and create initial

homogenous sections at locations where the alignment changes. Section 2.5 gives further

information on defining alignment. Aim for consistent alignment, although changes between

two adjoining alignment categories, or large changes in alignment over short lengths (<1km), are

acceptable.

5. Ideally, the same traffic volume category should apply to the whole homogenous section.

However, small changes in traffic volume, such as when the traffic volumes fall near the

boundary of two categories are acceptable.

6. Create a separate section for each direction of a divided road e.g. divided roads should have at

least one section for each direction. However, ignore short lengths (<1km) where the road

briefly changes from undivided to divided or vice versa.

During coding some adjustment to the homogeneous sections may be required, particularly where

there is significant change in roadside hazards. Sections should be defined so that there is

consistency in the roadside hazard coding and section breaks should be used where there is a clear

change in the roadside hazards. For example, if the road changes from a flat plain with occasional

trees on either side, to a road in a valley with a steep slope on one side and a drop off on the other,

these should form two sections.

Distinct changes in carriageway width may also influence the definition of homogeneous sections.


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2.3 DataFields

In addition to coding the road attributes a number of data fields should be recorded. The data fields

that are input to the IRR spreadsheet are shown in TABLE 2‐1.

TABLE 2‐1: IRR DATA FIELDS

Data Field Description

IRR Section

Reference Number

Section reference number selected by the user. Any value can be used e.g. 1,

2, 3; A1, A2, A3 etc.

IRR Homogenous

Section Name

Name given to each homogenous section to assist with referencing e.g. Levin‐

Otaki 1, Levin‐Otaki 2, Waikanae 1, Waikanae 2, Blockhouse Bay, Ponsonby

Coder Name Full name of person undertaking coding. It is recommended that the coder’s

organisation is also included e.g. John Smith (ABC Consulting)

Coding Date The date on which coding was undertaken

Street Level Data

Source

The data source that provides a street level view used to complete the coding

e.g. state highway video, Google Street View, drive over survey

Street Level Data

Source Survey Date

The date of capture of the data source used

Local Road/State

Highway

Denotes whether the section is a state highway or local authority road

Road Name The name of the road(s) or state highway number e.g. Henderson Road, State

Highway 1, Orchard East Road/Orchard West Road. Where the state highway

has an alternative name this should be entered here, and the state highway

number entered in the next field.

State Highway

Number

The number of the state highway e.g. SH1N, SH07. Not applicable to local

roads.

Section From

RS/Intersecting Road

Reference denoting start point of the section on the road being coded. For

state highways this is the route station number e.g. RS347, RS1026. For local

roads this will usually be the name of an intersecting side road, e.g. Oxford

Street. The intersecting side road chosen must be one that has just been

passed, when viewed in the direction of travel in which the road section is

being coded.

Distance From km The distance in kilometres from the state highway route station or

intersecting side road shown in “Section From RS/Intersecting Road”.

Section From RAMM

ID

The RAMM ID that applies at the start of the section being coded e.g. 2540,

663. This field is optional.


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Data Field Description

Section To

RS/Intersecting Road

Reference denoting end point of the section on the road being coded. For

state highways this is the route station number e.g. RS347, RS1026. For local

roads this will usually be the name of an intersecting side road, e.g. Oxford

Street. The intersecting side road chosen must be one that has just been

passed when viewed in the direction of travel in which the road section is

being coded.

Distance To km The distance in kilometres from the state highway route station or

intersecting side road shown in “Section To RS/Intersecting Road”.

Section To RAMM ID The RAMM ID that applies at the end of the section being coded e.g. 2540,

663. This field is optional.

Direction The direction of travel in which the road section is being coded i.e. Increasing

(I), Decreasing (D), Both (B) for state highways or Eastbound (EBD),

Westbound (WBD), Southbound (SBD), Northbound (NBD) for local roads. This

value should be consistent with the “from” and “to” references above.

Section Length km The length of the section in kilometres. This value should be consistent with

the “from” and “to” references above.

Section Location

Description

Description of the section location e.g. Rolleston, Dunsandel‐Heslerton Road,

South of Levin, Dunedin Central, South Dunedin, Ilam.

Coding Comments A field for coders to enter any comments they wish to make, such as

assumptions made, particularly where there is uncertainty in coding a

particular feature. For example, when coding the right side hazard risk, the

coder could comment: “aggressive vertical faces/unguarded drop part of

distance, low scrub/ low severity property hazards part of distance, so coded

as High overall”.

Fatal Crash Count

(5yr)

The number of fatal crashes that have occurred on the section over the most

recent five year crash period with data available e.g. the number of fatal

crashes from 2010 to 2014 occurring on the section. This field is not required

to calculate the IRR and is therefore optional.

Serious Crash Count

(5yr)

The number of serious injury crashes that have occurred on the section over

the most recent five year crash period with data available. This field is not

required to calculate the IRR and is therefore optional.

Minor Crash Count

(5yr)

The number of minor injury crashes that have occurred on the section over

the most recent five year crash period with data available. This field is not

required to calculate the IRR and is therefore optional.

Average AADT The average length weighted Average Annual Daily Traffic volume over the

section. Use the year that corresponds to the last year of the crash data used

e.g. if crash data is 2010 to 2014 then the 2014 AADT should be entered here.

This field is not required to calculate the IRR and is therefore optional.


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2.4 RoadStereotype Road stereotype is recorded by selecting one of five categories, as shown in TABLE 2‐2 below.

TABLE 2‐2: ROAD STEREOTYPE CATEGORIES

Categories Description

Unsealed Any road that is unsealed

Two lane undivided An undivided road with one lane in each direction

Multi‐lane undivided An undivided road with more than one lane in each direction. Includes roads

with two lanes in one direction and one lane in the other direction.

Divided ‐ traversable Divided road with a traversable median

Divided – non

traversable & one way

Divided road with a non‐traversable median, and one way streets.

A divided road with a non‐traversable median is one that will stop an out of control vehicle from

crossing the median. A non‐traversable median will typically have a safety barrier present and/or

10m+ separation between opposing traffic flows.

A divided road with a traversable median is one that has features that prevent vehicle movements

across the median but will not stop an out of control vehicle from crossing the median. Traversable

medians include kerb islands, closely spaced flexi‐posts, or a separation of less than 10m between

opposing traffic flows. See Section 2.1 for a definition of divided and undivided roads.

Where there is any ambiguity or overlap between categories, the category that appears higher in the

table should be selected e.g. if a road is unsealed and one way then the unsealed category should be

selected.

Homogeneous sections are defined based, in part, on road stereotype so aside from short changes in

road stereotype e.g. at short (<1km) passing lanes, the road stereotype should be the same over the

homogeneous length.

2.5 Alignment Alignment is categorised based on the degrees of turn per km. Four categories are used, as shown in TABLE 2‐3 and these can be coded using a geospatial dataset or manually using judgement.


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TABLE 2‐3: ALIGNMENT CATEGORIES

Categories Definition Description

Tortuous ≥300 degrees of turn/km The road is tortuous with consecutive curves and

numerous sharp (with typical radii of 350m to 500m)

and very sharp curves (with typical radii <350m), and

can generally be driven at less than 75km/hr.

Winding ≥150 and <300 degrees of

turn/km

The road is winding, with many consecutive curves and

sharp curves (with typical radii of 350m to 500m), and

can generally be driven at 75km/h‐85km/h.

Curved ≥50 and <150 degrees of

turn/km

The road is curved and has moderate curves (with

typical radii 500m‐1500m) and can generally be driven

at 85km/h‐100km/h, though some straight sections or

isolated sharp curves may also be present.

Straight <50 degrees of turn/km The road is straight or gently curved (typical radii

>1500m) and can be driven at 100km/h or more.

Alignment may vary over a homogeneous length, therefore the average category should be selected. If the average value falls half way between two categories, then the higher risk category (shown highest in TABLE 2‐3) should be selected. For example, over a 5km homogeneous length, if 4km is straight or gentle, 2km curved, and 400m winding, then the alignment should be coded as “straight or gentle”. If there is 2.5km straight or gentle and 2.5km curved, then curved should be selected. Homogenous sections aim for consistent alignment, although changes between two adjoining alignment categories, or large changes in alignment over short lengths (<1km), are acceptable.

2.6 CarriagewayWidth Carriageway width risk is rated by coding both lane and sealed shoulder width as shown in TABLE 2‐4 and TABLE 2‐5. These lane and shoulder widths should be measured or taken from asset management databases

where practicable. If data is not readily available then visual judgement can be used by comparing

the lane and shoulder widths to vehicles travelling on the road (a truck is generally 2.5m wide and

cars are typically between 1.8m and 2.3m wide).

TABLE 2‐4: LANE WIDTH CATEGORIES

Proposed Lane Width Categories Description

Narrow (<3.0m) Narrow lane width <3.0m is generally present

Medium (3.0m to 3.5m) Medium lane width 3.0m to 3.5m is generally present

Wide (>3.5m) Wide lanes >3.5m are generally present

If a road has no edgeline markings for a shoulder, then the lane widths are measured from the edge of seal, since a vehicle can be considered to be able to travel to the edge of the sealed surface.


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Where there is more than one lane, only the narrowest lane width is taken into consideration. However, cycle lanes and other special vehicle lanes, such as bus lanes, should be ignored. For unsealed roads or roads with no marked centreline, the lane widths are estimated using

judgement to determine the number of lanes based on travelled vehicle paths.

Where lane width varies along the homogeneous section, coding is based on the category that generally applies over the section. TABLE 2‐5: SEALED SHOULDER WIDTH CATEGORIES

Proposed Shoulder Width Categories Description

Very narrow shoulder (0 to <0.5m) Very narrow with little or no shoulder, <0.5m, is

generally present

Narrow shoulder (0.5m to 1.0m) Noticeable but narrow shoulder, 0.5m to 1.0m, is

generally present

Wide shoulder (>1.0m to 2.0m) Good wide shoulder, >1.0m to 2.0m, is generally

present

Very wide shoulder (>2.0m) Very wide shoulder, >2.0m, is generally present

The sealed shoulder width is measured from the centre of the painted edgeline (excluding audio

tactile ribs outside the painted edgeline) to the unsealed surface. If the edge of seal begins to break

up on the shoulder, the sealed shoulder width should be measured up to where the edge break

occurs.

Roadside parking should be coded as shoulder. However, ignore cycle lanes and other special vehicle

lanes.

For divided roads the left hand shoulder width is measured.

For undivided roads the lesser (minimum) of the left and right hand shoulder width is measured. Where shoulder width varies along the homogeneous section, coding is based on the shoulder width that generally applies over the section.

2.7 RoadsideHazards Roadside Hazards is one of the most important and difficult features to code. It involves assessing

hazard risk based on both the severity of the hazard and its offset, as well as determining which code

to use to represent the homogeneous section being rated.

Roadside hazards are rated separately for each side of the road. For divided roads, when recording

hazards on the right‐hand side, record hazards as measured from the right side edge of the divided

carriageway e.g. record hazards in the median and if there are no hazards present in the median

then record the next nearest hazard TABLE 2‐6 provides guidance on how to assess roadside hazard

risk based on the offset and severity of identified hazards. Appendix A provides example photos of

each roadside hazard risk category. The roadside hazard offset is recorded from the edgeline if one is

present. If there is no edgeline, then the offset is recorded from the edge of seal.


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For a group of point hazards to receive a particular risk score they need to be at a density that the

likelihood of the hazard being hit is relatively high. Therefore TABLE 2‐6 requires that 20+ point

hazards be present per kilometre (or one every 50m on average) for the particular hazard code to

apply. Similarly, if there are intermittent continuous hazards, such as structures/buildings or regular

short sections of cliffs and slopes, then these should occur at relatively regular intervals and cover at

least 50% of the length over which they occur. For example, if a section has short sections exposed

to cliffs over >50% of the length within 5m, then this should be coded as Severe.

If the hazards in question do not meet these density requirements, then judgement is required to

determine the average hazard code. For example, if part of the section has regular short sections

(<50%) exposed to cliffs within 5m (Severe) and metal barriers within 5m present (Minor) over the

remainder of the section on one side, then this could be coded as High or Moderate. It should be

coded as High if cliffs are present for close to 50% of the section and Moderate if there is

significantly less than 50%.

In cases where the roadside hazards change regularly over short sections the average hazard code

should be selected. For example, if the section is an open plain with intermittent trees and poles

(<20/km) then the average roadside hazard code should be selected. In this case if the trees and

poles are generally between 5m and 10m from the edge of seal then the hazard coding is alternating

between Moderate (where there are trees and poles) and Negligible (where there are no hazards)

and therefore the code Minor should be selected.

Finally, as the coding is being done over homogeneous lengths some judgement may be required to

determine the roadside hazard risk code that best represents the entire homogeneous section.

However, as stated in Section 2.2, if there is a distinct change in roadside hazard a new

homogeneous section break should be created.


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TABLE 2‐6: ROADSIDE HAZARD RISK WITH HAZARD SEVERITY AND OFFSET DESCRIPTIONS

IRR

Roadside

Hazard

Risk

IRR Roadside Hazard Risk Description Example Hazards

Severe Aggressive/severe continuous hazards

and cliffs, within 5m*

OR

20+ non‐frangible point hazards per

kilometre (1+ per 50m) or rigid

structures/bridges/buildings, within

5m

Aggressive/severe continuous hazards can

include:

Aggressive vertical faces

Deep drainage ditches

Cliffs with steep or high drop offs, and/or

deep water, that would result in death

regardless of speed

Examples of non‐frangible point hazards

include:

Trees, signs, posts, poles >=10cm

diameter

Large boulders (>=20cm diameter)

Unprotected barrier ends

High Cliffs or deep water at 5m to <10m*

Roll‐over up‐slopes and downslopes

(e.g. >15⁰ and >1m high) at <5m*

Moderate Aggressive/severe and moderate

continuous hazards at 5m to <10m,

excluding cliffs and deep water*

OR

20+ non‐frangible point hazards per

kilometre (1+ per 50m) or rigid

structures/bridges/buildings at 5m to

<10m

OR

Car parking or semi‐rigid structures or

buildings at <5m*

Aggressive/severe and moderate continuous

hazards can include:

Aggressive vertical faces

Deep drainage ditches

Roll‐over up‐slopes and downslopes (e.g.

>15⁰ and >1m high)

Non‐frangible point hazards can include:

Trees, signs, posts, poles >=10cm

diameter

Large boulders (>=20cm diameter)

Unprotected barrier ends

Minor Metal and concrete safety barriers at

<5m*

Car parking or semi‐rigid structures or

buildings at 5m to <10m*


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IRR

Roadside

Hazard

Risk

IRR Roadside Hazard Risk Description Example Hazards

Low Metal and concrete safety barriers at

5m+*

Low severity property damage hazards

at any distance*

All hazards at >=10m*

Low severity property damage hazards can

include:

Kerbs

Wire‐rope barriers

Level and safe slopes (<=15⁰ and <=1m

high) with no hazards

Frangible trees, posts, poles <10cm

diameter

*over 50%+ of the length where they occur intermittently

2.8 LandUse The Land Use feature takes into account the surrounding land use. The selection of the most

appropriate code can also be informed by the presence of accessways and intersections (TABLE 2‐7).

The purpose of the land use code is to give an indication of the likely level of activity present on the

road. This includes pedestrian and cyclist activity along and across the road, as well as vehicle

movements – parking and driveway manoeuvres and vehicles turning to and from intersections and

accessways etc.

Code changes in land use where the change is present for 1km or more.

TABLE 2‐7: LAND USE

IRR Land Use &

Access

Categories

Description

Commercial strip

shopping

Characterised by numerous shops facing the streetfront with high levels of

activity, particularly pedestrians, cyclists and high occupancy on‐street parking

resulting in many vehicle movements to and from the road. Regular

intersections and accesses will also be present.

Commercial big

box/Industrial

Large (big box) shops and/or industry/factories with intermittent large

accessways and intersections leading to large car parking areas. Regular

intersections and smaller accesses are also likely to be present. Some

pedestrian and cyclist activity may be present.

Urban residential Urban residential area dominated by housing with frequent driveways and on‐

street parking. Regular intersections and accesses are present. Pedestrian and

cyclist activity is also likely to be present, particularly at certain times of the

day.

Rural towns Rural town with mixture of residential and some shops. Some intersections

and accesses are present. Some pedestrian and cyclist activity may also be

present.


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IRR Land Use &

Access

Categories

Description

Controlled access Road with roadside development and controlled access, such as an urban

state highway or arterial where there are few accesses to the road e.g. as a

result of a service road. Some pedestrian and cyclist activity may also be

present but with few crossing movements.

Rural residential Rural area with accesses present to private dwellings and farms. There may be

the occasional industry/factory present. Some pedestrian and cyclist activity

may also be present, particularly at certain times of the day, but with few

crossing movements.

Remote rural Only occasional accesses and intersections are present. Surrounding land is

rural with few houses and almost no industry.

No access No accessways or at grade intersections are present and pedestrians and

cyclists are not allowed e.g. motorway.

When coding, consider both what the adjacent land use looks like and how it is accessed from the road as the purpose of coding this feature is to capture the impact of land use on vehicle movements and the general level of activity present that impacts on the road. For example, if there are commercial big box retail shopping centres present and these are accessed from a highway from a few intermittent intersections then a judgement will need to be made as to whether this should be coded as Commercial Big Box/Industrial or Controlled Access. If there is uncertainty around which category to select then choose the category that appears higher

in the table e.g. choose commercial strip shopping over rural towns if coding a section in a rural

town that has a long length (1km+) of commercial strip shopping.

2.9 IntersectionandAccessDensity The at‐grade intersection and access density should also be recorded as shown in TABLE 2‐8 and

TABLE 2‐9.

TABLE 2‐8: AT‐GRADE INTERSECTION DENSITY

At‐Grade Intersection Density

10+ intersections / km

5 to <10 intersections / km




<1 intersection / km


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TABLE 2‐9: ACCESS DENSITY

Access Density

20+ accesses / km

10 to <20 accesses / km



1to <2 accesses / km

<1 access / km

The appropriate intersection and access density category should be selected by counting the number

of intersections and accesses and dividing by the homogenous section length to determine the

average.

Where intersection density or access density changes significantly over 1km or more, then a break

should be made in the homogenous section. Where a significant change occurs over a short length

(<1km) then judgement should be used to determine whether a section break is required, depending

on how large the change in density is.

2.10 TrafficVolume Traffic volume is coded using four broad categories based on Annual Average Daily Traffic (AADT) volumes as shown in TABLE 2‐10. TABLE 2‐10: TRAFFIC VOLUME CATEGORIES

IRR AADT Categories

<1,000 veh/day

1,000‐<6,000 veh/day

6,000‐<12,000 veh/day

12,000+ veh/day

The traffic volume should be recorded for the carriageway being coded. For undivided roads the traffic volume in both directions should be coded, and for divided roads the traffic volume on the single direction carriageway being coded should be recorded. For divided roads, if the traffic volume is not available by direction, then the two‐way traffic volume should simply be halved. Homogeneous sections should be defined so that the whole section falls into the same traffic volume category, however, small changes in traffic volume that fall outside of a traffic volume category are acceptable. Traffic volume should be coded using available count data such as that held in asset management databases.


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3 IRRModel

Infrastructure Risk Rating is a multiplicative model as shown in EQUATION 3‐1 below.

EQUATION 3‐1: IRR MODEL

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Where IRR Score = <0, set IRR Score equal to 0

TABLE 3‐1 shows how the IRR Score is converted to an IRR band

TABLE 3‐1: IRR BANDS IRR Score Rural Urban

0 to <0.8 Low Low

0.8 to <1.2 Low-Medium Low

1.2 to <1.6 Medium Low

1.6 to <2.0 Medium-High Low-Medium

2.0 to <2.4 High Medium

2.4 to <2.8 High Medium-High

2.8+ High High

Rural and urban classification is based on the coded land use category. Corridors with the following

land use categories are assessed as rural corridors:

No Access

Rural Residential

Remote Rural

Urban thresholds are applied to corridors that are coded with the following land use categories:

Commercial Big Box/ Industrial

Commercial Strip Shopping

Urban Residential

Controlled Access

Rural Town


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TABLE 3‐2 to TABLE 3‐9 show the risk scores associated with each attribute for each of the eight IRR

features.

TABLE 3‐2: ROAD STEREOTYPE RISK SCORES

Road Stereotype Risk Score

Unsealed 10

Two lane undivided 3.7

Multi-lane undivided 3.4

Divided - traversable 3.0

Divided - non-traversable 1.0

One Way 1.0

TABLE 3‐3: ALIGNMENT RISK SCORES

Alignment Risk Score

Tortuous 6.0

Winding 3.5

Curved 1.8

Straight or gentle 1.0

TABLE 3‐4: CARRIAGEWAY RISK SCORES Lane Width

Shoulder Width <3.0m – Narrow 3.0m to 3.5m - Medium >3.5m – Wide

0m to <0.5m - Very Narrow 2.01 1.79 1.58

0.5m to 1.0m - Narrow 1.79 1.45 1.18

>1.0m to 2.0m - Wide 1.22 1.00 0.85

>2.0m - Very Wide 1.00 0.78 0.66

TABLE 3‐5: ROADSIDE HAZARD RISK SCORES

Roadside Hazard Risk Risk Score

Severe 2.80

High 2.28

Moderate 1.43

Minor 0.67

Low 0.40


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TABLE 3‐6: LAND USE RISK SCORES

TABLE 3‐7: AT‐GRADE INTERSECTION DENSITY RISK SCORES

At‐Grade Intersection

Density Risk Score

10+ intersections/km 5.00

5 to <10 intersections/km 2.60




<1 intersection/km 1.00

TABLE 3‐8: ACCESS DENSITY RISK SCORES

Access Density Risk Score

20+ accesses/km 1.30

10 to <20 accesses/km 1.10




<1 accesses/km 1.00

Land Use Risk Score

Commercial strip shopping 5.00

Commercial big box/Industrial 4.00

Urban residential 3.00

Rural towns 2.50

Controlled access 2.00

Rural residential 1.50

Remote rural 1.00

No access 1.00


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TABLE 3‐9: TRAFFIC VOLUME RISK SCORES

Traffic Volume Risk Score

<1,000 veh/day 1.00

1,000-<6,000 veh/day 1.40

6,000-<12,000 veh/day 2.20

12,000+ veh/day 3.00


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4 AutomatedProcessOverview A geospatial process has been developed to expedite IRR coding so that it can be widely applied in a

cost effective manner. While this process has some limitations and is likely to be less accurate than

manual coding for some attributes, it does have the benefit of providing an objective network‐wide

assessment that eliminates inconsistencies between coders undertaking a manual assessment.

Results from testing the automation process are promising; achieving an R2 value of 0.92 for

approximately 134km of Top of the South region network. Of the 51 sections trialled, 84% fell within

the same IRR band and only one section1 fell more than one band away from the band determined

from manual coding.

4.1 GeospatialProcessforCreatingHomogenousSections The geospatial process developed for creating homogenous sections is outlined in FIGURE 1 below.

As per the Speed Management Framework, the primary factor in determining a safe and appropriate

speed is the surrounding land use. Corridors with a uniform land use are then segmented further

based on changes in IRR attributes that contribute significantly to the IRR Score. Each step of the

process incorporates thresholds developed to avoid segmenting corridors due to short changes in

road attributes such as overtaking lanes or intersection approach medians.

FIGURE 1 IRR AUTOMATED SEGMENTATION PROCESS

1 This has since been further improved through refining the automated corridor segmentation process that was originally trialled.

Segmentation Thresholds:

Urban: 250m, Rural: 500m

Urban & Rural: 1km

Rural: 1km

Urban & Rural: 1km

IRR Homogenous Corridors

4th Segmentation: Traffic Volume

3rd Segmentation: Alignment (Rural only)

2nd Segmentation: Road Stereotype

1st Segmentation: Land Use

Centreline Aggregated by Posted Speed Limit & Road Name


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4.2 IRRAttributesCodingAutomation The coding of each IRR feature has been automated. For some features, existing geospatial data is

used, while for others, approximations are made based on the value of other IRR features. Where a

feature’s value has been approximated, these values must be manually checked and updated when a

section is identified for speed management review.

4.2.1 RoadStereotypeCodingAutomation The coding of road stereotype has been automated by drawing from the Road Asset Maintenance

Management (RAMM) database. The RAMM database includes number of lanes, divided/undivided

and whether the road is sealed or unsealed. All divided roads with a median barrier are assumed to

be non‐traversable, and divided roads without any barrier recorded are assumed to be traversable.

4.2.2 AlignmentCodingAutomation Alignment values are coded from the outputs of a geospatial model that assigns curvature based on

degrees of turn per km.

4.2.3 CarriagewayWidthCodingAutomation The IRR model uses a matrix of lane and shoulder width to determine a carriageway risk score.

However, only the width of the carriageway is available in RAMM. As such, lane and median widths

are assumed in order to determine shoulder widths, as follows:

All local roads are assigned a lane width of 3.3 metres

All state highways are assigned a lane width of 3.6 metres

Roads with a road stereotype of “Divided – traversable” are assigned a 0.5 metre median

width

4.2.4 RoadsideHazardRiskCodingAutomation The coding of roadside hazard risk is the most difficult to automate. As such, roadside hazard risk is

estimated based on the land use and alignment codes, as shown in TABLE 4‐1.

Hazards are also identified manually where possible using high quality spatial imagery and

topographic maps.


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TABLE 4‐1: ROADSIDE HAZARD RISK CODING AUTOMATION

Land Use Code Alignment Code Approximated Roadside

Hazard Risk

No Access Any alignment Minor

Controlled Access Any alignment High/Moderate*

Urban Residential Any alignment Severe/Moderate*

Commercial Big Box/Industrial Any alignment Severe/Moderate*

Commercial Strip Shopping Any alignment Severe/Moderate*

Remote Rural Tortuous alignment High

Remote Rural Any alignment other than

tortuous

Moderate

Rural Residential Any alignment High/Moderate*

Rural Towns Any alignment Severe/Moderate*

*where more than one category is shown the average risk score associated with the categories listed

is used

4.2.5 LandUseCodingAutomation Land use coding has been automated using urban and rural boundaries and the density of residential

and commercial developments sourced from planning zones, Open Street Map (OSM) and Land

Information New Zealand (LINZ) datasets.

4.2.6 IntersectionDensityCodingAutomation Intersection density is coded by generating geospatial points at each intersection and calculating the

number of points per km for each corridor.

4.2.7 AccessDensityCodingAutomation Access density coding is assumed based on a combination of land use and posted speed limit as

follows:

1.35 ln 7.56 8.26 8.94 9.32 10.2611.13 11.17

Where:

AD = Access Density Bin

SL = Speed Limit (km/h)

CAU = Controlled Access (binary variable which equals 1 if land use is Controlled Access)

RemR = Remote Rural (binary variable which equals 1 if land use is Remote Rural)


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CBBI = Commercial Big Box/Industrial (binary variable which equals 1 if land use is Commercial Big

Box/Industrial)

RRes = Rural Residential (binary variable which equals 1 if land use is Rural Residential)

RT = Rural Town (binary variable which equals 1 if land use is Rural Town)

UR = Urban Residential (binary variable which equals 1 if land use is Urban Residential)

CSS = Commercial Strip Shopping (binary variable which equals 1 if land use is Commercial Strip

Shopping)

If ADB < 1.5, then code as <1 accesses/km

If ADB < 2.5, then code as 1 to <2 accesses/km




If ADB > 5.5, then code as 20+ accesses/km

4.2.8 TrafficVolumeCodingAutomation Traffic volume data stored in RAMM is used to automate the coding of traffic volume.


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AppendixA:RoadsideHazardRatingExamples


23

Roadside

Hazard

Risk

Roadside Hazard Risk

Description

Example Photos

Severe Aggressive/severe continuous hazards and

cliffs, within 5m*

OR

20+ non‐frangible point hazards per kilometre

(1+ per 50m) or rigid

structures/bridges/

buildings, within 5m

High Cliffs or deep water at

5m to <10m*

Roll‐over up‐slopes and downslopes (e.g. >15⁰

and >1m high) at <5m*

Moderate Aggressive/severe and moderate continuous

hazards at 5m to <10m,

excluding cliffs and

deep water*

OR

20+ non‐frangible point hazards per kilometre

(1+ per 50m) or rigid

structures/bridges/buil

dings at 5m to <10m

OR

Deep ditches: >1m

deep, @ <5m

Roll-over slope (>15⁰ and >1m high),

@ <5m

Trees >10cm

diameter, @ <5m

Non-frangible poles,

@ < 5m

Ri id b ildi / t t @ 5

Semi-rigid structures or buildings, @ <5m

Water hazard @ <5m

Trees (non-frangible point hazards), @ 5m to <10m Roll-over slope (>15⁰ and >1m high),

@ 5m to <10m

Roll-over slope (>15⁰ and >1m high) @ <5m

Poles (non-frangible point

hazards), @ 5m to <10m

Rigid structures/buildings,

@ 5m to <10m

Aggressive vertical face,

@ <5m

Car parking @ <5m

Drop-off and water hazard @ 5m <10m


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Roadside

Hazard

Risk

Roadside Hazard Risk

Description

Example Photos

Car parking or semi‐

rigid structures or

buildings at <5m*

Minor Metal and concrete

safety barriers at <5m*

Car parking or semi‐

rigid structures or

buildings at 5m to

<10m*

Low Metal and concrete

safety barriers at 5m+*

Low severity property

damage hazards at any

distance*

All hazards at >=10m*

*over 50%+ of the length where they occur intermittently

Lightweight structures

e.g. Isolated rural letter boxes (<10cm diameter), hoardings

Small trees <10cm diameter

Safety barriers @ <5m

Only low severity property damage hazards within 10m

Only low severity property damage hazards

within 10m

Semi-rigid structures or buildings at 5m to <10m

Hazards 10m+, low severity property damage hazards

<10m

Documents

Infrastructure Risk (IRR)Manual - NZ Transport Agency · Infrastructure Risk Rating Manual 2 2 Infrastructure Risk Rating Coding To assess risk and determine an Infrastructure Risk