HF Guiding Principles in Road Design

International Seminar on National Road Development Strategies & Road Safety on Improved Highways

School of Planning and Architecture, New Delhi, India, 14-19 March 2011

HF GUIDING PRINCIPLES IN ROAD DESIGN: SPATIAL PERCEPTION OF THE DRIVER

Dr. Sibylle Birth Intelligenz System Transfer Ltd., Germany

[email protected]

ABSTRACT

Why do accidents happen in certain places? What does the human perception have to do with driving a car? And how does the road with its surrounding influences the driver´s performance? These questions occupy traffic planners, road authorities and scientists of engineering science and pyschology since the invention of cars at the end of the 19th century. The paper gives a short introduction about findings of modern human factors guiding principles based on the laws of human space perception.

It is well known that Human Factors have an enormous influence on the safe handling of technical systems. Human Factors can be described as people’s contributions to damaging events. It is the generic term for those psychological and physiological patterns which are verified as contributing to operational errors in machine and vehicle handling. In the case of road safety, the Human Factors concept considers road features that influence a driver’s right or wrong behaviour. It considers the causes of driver operational error as the first step in a chain of actions which may proceed to an accident. Many of the often-observed operational errors result from the direct interaction between road characteristics and the driver’s reaction characteristics. Because the driver’s reaction characteristics cannot be changed, attention should be focused on a self-explanatory road design.

Results of an audit of 10 international design standards show, that only about 25% of the human factors demands of space perception are integrated in the design standards. Wheares the questions of geometry and alignment dominate the design process, the designer is not aware that he designs a complete architecture of a perceptional space of the driver. So he is mostly concerned with all the important questions how to find proper location, alignment, geometry and to realize that with a smaller and smaller budget. The question of space perception don’t plays that role that it should have concerning road safety. Since about 65% of accidents could be avoided if the following rules would be known by designers and integrated in the design process:

I. 6-Second Rule: Road users must have enough reaction time!

II. Field of view Rule: Road must offer a safe field of view!

III. Logic Rule: Road must follow driver’s perception logic!

Examples and propositions will be presented to help designers to be prepared to implement new standards that incorporate a safe cohabitation between roads and human factors of space perception. The detailed examples and sketches allow the engineer to

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HF Guiding Principles in Road Design:

Spatial Perception of the Driver



understand the relationship between wrong road features and Human Factors related accidents. They can be used as a kind of checklist in the “on-the-spot” investigation of accident points or in Road Safety Inspections. They can also be used to qualify planning and construction process in Road Safety Audits. Practical examples are given to illustrate simple low cost measures to improve black spots.

1.0 BACKGROUND

Most of the traffic accidents occur because of driving mistakes. Some of the driver’s errors are errors of judgement but others are induced by misleading road features.

It is well known that Human Factors have an enormous influence on the safe handling of technical systems. In many technical subjects like household machines, vehicles, ships, aircraft and in the world of production the Man-Machine-Interface (MMI) is well explored and special design standards are developed to prevent human errors or at least to create a failure-forgiving and self-explanatory road design.

However, often drivers are overstrained by certain road and traffic conditions and then react confusedly. Such situations can be identified by statistics as road sections with accident lines or accident spots. The Human Factors Concept will contribute to enlighten such situations step by step and to adjust them to the capabilities of the road users in order to avoid such accidents in the future.

The interaction between driver and vehicle, as well as between vehicle and road, have always been in the focus of interest. Whereas the interaction between the driver and the road has been paid only minor attention to in the past. This interaction is the subject of the Human Factors concept. It shall close an often complained gap in the prevention of accidents (see Fig. 1).

Fig. 1: The Human Factors concept closes a gap in the system of road safety [1]





2.0 Definition: Human Factors

Human Factors has been a professional term ever since around 1930. It is defined as the

contribution of human nature in the development of a technical dysfunction or failure in

handling machines and vehicles. Human Factors is not human behaviour or human

performance. The term is abbreviated to “HF”. The HF concept uses certain words and

terms, which are not commonly used in the field of accident research:

An operational error is the first but unintended action within the chain of actions, which

may result in a driving mistake. It is caused by a lack of information or a lack of information

in the interaction between driver and road. In most cases it can be corrected

spontaneously. An operational error, left unchecked, can become a driving error. Often

the driver is able to correct even the driving error. If not, it could cause an accident.

The HF concept considers the driver’s operational error as the first step in a chain of

actions which may proceed to an accident. Many of the often-observed operational errors

result from the direct interaction between road characteristics and the driver’s reaction

characteristics. The road features set the behaviour of the driver. Since the driver’s

reaction characteristics cannot be changed, the attention should be focused on the road

characteristics. This deduction makes it possible and obligatory to take into consideration

the principles of the driver’s perception and reacting, when roads are planned and

constructed.

The concept of self-explanatory road design tries to reduce the probability of operational

errors and thus also to reduce the probability of driving errors. This lets directly to expect

a decline in the frequency of accidents. But the extent of damages resulting from an

accident depends on other influences (condition of the vehicle, car and road interaction,

surface etc.).





Fig. 2: The context of operational error – driving error - accident [1]

Three classes of HF-Mistakes in road design

The 6-Second-Rule: The road should give the driver enough time

We are all road users and driving a car has become an activity that includes nearly everybody. Modern life excludes almost nobody from participating in motor-operated road traffic. Completely fit drivers share the road with persons who are physically and/or mentally impaired, distracted, or who have a lack in concentration, who are slow-reacting, tired or overexcited. In road traffic you can find the whole spectrum of abilities and capabilities.

It is a singularly false assumption that car drivers, of all people, should be able and willing to summon continuously increasing power, attention and physical strength. They are not exceptional people. They have limited capabilities to act and react. The time it takes to adapt from one traffic situation to the next, or the time to adjust for new requirements, takes much longer than one would think.

Proportions Incidents and Accidents

Operational error : Driving error : Accident

= 5000 : 500 : 20

INCIDENT (99.6%) ACCIDENT (0.4%)





Instead of fractions of a second (“simple stimulus–reaction time”), it takes the average driver at least 4 to 6 seconds to adapt to a new driving requirement (“perception–orientation-decision time”). When driving at a speed of 100 km/h, the driver covers a distance of up to 300 m during this time (taking account of the braking time). A user-friendly road will give the driver the necessary time to adapt. It will give him the time he needs to safely re-organise his driving programme.

Average drivers need 4–6 seconds to completely change their driving programme. A user-friendly road will allow an appropriate adjustment of driver behaviour to a new situation. It is necessary to arrange transition zones, remove visibility restrictions, make junctions perceptible or use markings to warn drivers at least 6 seconds before critical points such as junctions, curves, railway crossings, bus stops or bicycle paths.

Fig. 3: Transition area for a safe change of the driving routine [1]

perception/detection

decision

Notice:

It takes the average driver 4–6

seconds, to change his driving

routine completely. At a speed of

100 km/h this results in a way of

up to 300 m.

Conclusion: Don’t surprise the

driver! At a minimum of 300m

before a critical point:

- Remove visual obstacles such as crests, curves, vegetation and buildings prior to critical points. If useful, construct traffic islands.

- Use special visual advisories on road surfaces, such as coloured areas, signs, pavement changes.

- Install speed limits, prohibit overtaking, set up warning signs.





Fig. 4: Minor road not visible early enough: unexpected braking and high speed at this point cause rear end collisions [8]

Fig. 5: Improved situation by countermeasures of space perception[8]

THE FIELD OF VIEW-RULE: THE ROAD MUST OFFER A SAFE FIELD OF VIEW

Motorised driving changes the field of view much more rapidly than any other movement. Changes in the field of view cause pleasurable and stimulating emotions in most people. These emotions are involuntary and cannot be suppressed. Monotonous or high-contrast periphery, optical misguidance and illusions affect the quality of driving. The field of view can either stabilise or destabilise drivers, and can tire or stimulate them. For example, a user-friendly, self-explanatory road avoids monotony and optical guiding lines that are not parallel to the road edge or optical guiding lines with gaps. It also avoids dominant eye-catching objects that attract the view axis away from the road alignment.

A good-quality field of view effectively safeguards the driver and keeps him from drifting to the edge of the lane or even leaving it. The field of view also affects the tracking precision. If the road provides the driver a good visual „hold“ by running in a slight trough, then the driver will steer his car at a sufficient distance away from the centre line. But when the





road runs along the top of a plateau without optical stabilising aids, then the driver will tend to drift towards the centre line.

Fig. 6: Destabilisation (left) and stabilisation (right) of keeping on track depends on road design [1]

Also the orthogonality of the surrounding environment can affect tracking precision. Trees or buildings can create a non-orthogonal impression that especially affects field-dependent drivers who tend to swerve and make spontaneous steering manoeuvres to compensate the optical misperception.

Fig. 7: Destabilisation by non-orthogonal impression: drivers spontaneously try to correct direction [12]

Fig. 8: Destabilisation by misguiding orientation lines: the suspension disturbs the balance, users tend to go/drive to the right [11]

Driving is a dynamic process that demands a lot of precise and accurate actions from the driver. Nevertheless space perception and movement is predominantly subconscious. There are certain stereotypes of space perception that influence the driver. These have to be considered in order to support the driver and stabilise his orientation.

- Space perception: space is perceived by humans as an oval. To perceive this space and identify all relevant information the eye scans this oval in small interior





circles of 15° in a counter-clockwise direction. All of the collected information forms a three-dimensional space.

- This three-dimensional perception ends after 8 m and beyond this point space can only be perceived in two dimensions. Despite this people can still judge distances and estimate which of two objects is nearer to the observer. However, this is the result of mental processes of the brain based on knowledge about regular sizes of objects, perspective relations and characteristics of textures. These are the reasons why the visual perception of space is very error-prone and susceptible to optical illusions and thus needs clear and unambiguous spatial information.

Fig. 9: Best practice example from Canada: well-structured fields of space with clear reference lines [11]

Fig. 10: Best practice example from Denmark: well-structured fields of space with clear reference lines [12]

- Left-hand phenomenon: one not very well known stereotype of human orientation and movement is the so called left-hand phenomenon. It is evident in humans as well as animals and can be described as a natural tendency to circular, counter-clockwise movements. For example, wild game separated by a hunter or any other incident than it will run after a short spin to the right in a long left-handed circle counter-clockwise back to the starting point. Counter-clockwise movements are often much easier to perform for humans than clockwise rotations. This can be observed in many examples. The left-hand phenomenon explains why right-hand curves are more difficult for drivers. For road designers, this means that the





difficulties in driving through a curve that are described below are even more crucial for right-hand curves.

Fig. 11: Left-hand phenomenon: in ancient and modern stadiums the running direction is always Counter - clockwise [11]

Driving reliably through a curve is also critically dependent on the quality of field of view. Best driving results are achieved when the driver has an unobstructed through the inside of the curve and the outside of the curve has a closed optical framing.

The driver’s responses to inner bends which are obstructed and especially to a fragmentary or even non-existent framing of outside bends are spontaneous speed changes and steering manoeuvres.

Therefore it is necessary not only to arrange the bend according to the technical rules with a constant radius, but also to design the field of view safely. Even a correctly designed bend can become dangerous for the driver by two characteristics:

- when the inside bend is obstructed by buildings, plants or geological formations,

- when the outside bend has gaps in its framing or is completely free and not framed by buildings, plants or geological formations.

Lots of accidents happen when one or both optical characteristics can be obseved. Each

of these two attributes also occurs alone and will cause the driver to spontaneously

changes in direction and speed while driving through such a bend.

Fig. 12: Destabilisation of the driver [1]





By misleading framing of outside bend and covered inside bend (left); corrected by a cover parallel to road’s edge

By framing with gaps in the outside bend (right); corrected by covering the misleading optical orientation line by a dominant orientation line parallel to road’s edge

The dependencies between the field of view characteristics and the driving behaviour can be assigned into three classes:

1. The number of objects that contrast with the background, determines the optical density of the field of view.

It affects v85 (speed below which 85% of all users of that road section drive).

2. The orderliness of the side framings determines the symmetry and rhythm of the lateral road space, the lateral space structure. It affects lane keeping.

3. The shape of the space in the driving direction determines the perceived spatial depth structure. Together with the depth of field of view it has an influence on the reliability of direction and the speed v85.





Fig. 13: Distance illusion: Road edge and planting line are

not parallel after a reconstruction and cause a

perspective illusion. Drivers overestimate the

distance up to the curve, run-off-road accidents

occur. [7]

Notice: Drivers continuously strive to optimise their field of view as long as they are not diverted by operational actions, offers of information or communication. The steering wheel, accelerator and brake pedals become control elements which contribute to the achievement of the comfortable field of view situation. Drivers correct their field of view by a single intense or several driving operations: Conclusion: Don’t misguide the driver! Avoid

- Monotonous approaching sec-tions / surroundings of a road

- Long + far visible approaching sections before critical points

- Unsymmetrical and/or different-high superstructures and those which are non-parallel to the visual axis

- Objects, sticking out of the road scenery, e.g. trees, buildings, technical facilities

- Optical guiding lines, which are non-parallel to the road edge e.g. markings, hard shoulders, crash barriers, plants, …

- Optical guiding lines with gaps - Dominant eye-catching objects with

distraction from the road direction or from critical points

- Optical illusions, caused e.g. by non parallel orientation lines

Create

- Rhythmic sinouos road alignment

- symmetry of superstructures - complete framing of outside bends, Cover

- nonparallel optical guiding lines that lead to optical illusions

- asymmetrical overstructures - non vertical orientation lines





Fig. 15: Lateral space structure

Wrong: asymmetrical super-structure leads to confusion, driver drifts to the ’left lane Reduced: Deficit covered by planting.

3.0 THE LOGIC-RULE:

ROADS HAVE TO FOLLOW DRIVER’S PERCEPTION LOGIC

The driver follows the road with an expectation and orientation logic formed by his experience and recent perceptions. They affect his perception and reactions. The perception of the lane, the edge of the lane and the lane periphery produce a general view.

The same principle also works when climbing stairs. Already after a few steps, the motion balance is adjusted to the sequence of steps just perceived. In most cases this is an unconscious process. If one step has a different height, the motion balance will become considerably disordered. The result is stumbling and falling.

And similar to the intuitive reaction to the height, depth and width of steps when climbing stairs, the driver reacts to the road elements. Unexpected abnormalities disturb a mostly automated chain of actions, and may cause drivers to “stumble”. Several critical seconds pass before the disturbance can be processed. Therefore planners should try to keep road characteristics flowing in a logical sequence. They should introduce inevitable changes as early and clearly as possible, and exclude any sudden changes that would confuse the driver.

Many international guidelines also demand this for the layout of roads (e.g., the German guideline for line management, abbreviated RAS-L). It contains design principles for continuous spatial line management. Note: discontinuous radii of consecutive bends increase the risk of accidents. Therefore, the modification of “stumble points” as well as the planning of new sections of a road always has to be adjusted to the existing road characteristics before and behind this point in order to exclude unexpected changes.





Fig. 16: Continuous and discontinuous bends in a road

(RAS-L, Germany) [5]

Fig. 17: Invisible town entrance (150 m ahead) [8]

4.0 CONCLUSIONS

4.0.1 POSSIBILITIES FOR DESIGNERS TO IDENTIFY HUMAN FACTORS DESIGN DEFICIENCIES

In four Human Factors training courses for road planners, constructors and accident commissions it was observed, that the classes of accident triggering HF mistakes in road design have different difficulties for the road engineers. A training course was planned and realized for 21/2 days to answer the evaluation question which HF mistakes participants of a training course can identify before and after the Human Factors training and what conclusions for the instruction could be drawn.

There were 34 road engineers from Germany, Spain, Netherlands, Slovenia, Finland and Sweden. A little contest was organised between the investigation teams to improve the learning results. You can see an overview of the learning results in table 1.

Notice:

When choosing his speed, the driver follows

his expectation, gained in past and recent

times. Breaking and changes of logic cause

operational errors which can lead to

accidents.

Conclusion: Don’t confuse the driver!

Avoid

- Continuing road characteristics despite a change of function („town entrance effect“).

- Change of the road’s course is contrary to eye-catching objects (“city by-pass dilemma“).

- Sudden changes of road characteristics are contrary to the normal driving behaviour („effect of habit and routine“).

- Sudden change of the driver’s strain because of a flood of information („sign post forest“, (accumulation of critical points).

- Unusual, irregular or illogical design placement of signs and other road side facilities.

wrong town entrance





Table 1: Statistical rate of identified HF design mistakes, before and after an HF

training course with 34 international participants [9]

Rate of identified HF design deficiencies

Before After

1. Deficits 6-Second Axiom 35% 66%

2. Deficits Field of View Axiom 13% 29%

3. Deficits Logic Axiom 27% 48%

The table shows that the content and procedure of the training course was appropriate to achieve a considerable increase in knowledge about Human Factors demands. The three half-day units with “on-the-spot” investigation and feedback ensure a practical learning on a good level. It was easiest for designers to identify deficits in road design concerning the 6-Second Axiom. This result is explainable because the necessity of a clear announcement of critical points and the use of transitions is internationally well known and often practised.

Another result was that the training leads to a doubling in the detection rate concerning the Field of View Axiom. However, because there is naturally a low basic knowledge about the laws of space and speed perception the detection rate remains after the training course at a lower level. But the engineers stated they learned to see a road with new eyes and this field was the most interesting and important for them.

The improved detection of design deficits concerning the Logic Axiom is sufficient because the essential deficits were identified. So the conclusion can be drawn that the knowledge about user demands and Human Factors design deficiencies can be integrated quickly and easily in the improvement of road safety by all responsible road authorities.

4.0.2 RESULTS OF HUMAN FACTORS AUDIT OF 10 INTERNATIONAL DESIGN STANDARDS

In the last three years the subgroup “Human Factors” of the Technical Committee TC1.1

Safer Road Infrastructure audited 10 international design standards if Human Factors

principles of space perception are integrated in the design principles. The result was

remarkable as shown in the following table 2.





Table 2: General voting table of HF-Audit of 10 international design standards

[13]

Yes: HF requirement is fully integrated in the standard

Partly: HF requirement is partially integrated but it is not mentioned that it is a HF need

NO: no such term/requirement is mentioned in the standard

YES

(Number of

countrys)

PARTLY (Number

of countrys)

NO

(Number of

countrys)

I. 6 Second Rule - Give enough time! 4 3 3

I.1. Transition zone 5 4 1

I.2. Perception and Visibility 2 8 0

II. Field of View - give reliable orientation and guidance!

0 8 2

II. 1. Optical density of the field of view - speed management

1 5 4

II. 2. Fixation objects in the lateral roadside environment support optimal lane tracking

0 6 4

II. 3. Depth of field of view - speed management

0 7 3

III. Logic Rule - give constistent design and signing!

2 6 2

III. 1. Town entrance (change of function without change of roads optical characteristic)

4 1 5

III. 2. City by-pass dilemma (change of direction despite the eye catching old course)

0 3 7

III. 3. Effect of pre-programed habits/routines (changes of road require relearning)

1 7 2

III. 4. Multiple critical points occur concurrently

5 0 5

III. 5. Deficiencies in traffic control devices

7 3 0

Fulfilled out of 10 Basic HF-Demands 25% 44% 31%





Only about 25% of the human factors demands of space perception are integrated in the design standards. Whereas the questions of geometry and alignment dominate the design process the designer is not aware that he designs a complete architecture of a perceptional space of the driver. So he is mostly concerned with all the important questions how to find proper location, alignment, geometry and to realize that with a smaller and smaller budget. The question of space perception don’t plays the role it should have in road safety. About 65% of accidents could be avoided if Human Factors rules would be known by designers and integrated in the design process.

By that it would be possible to reduce the probability of operational errors and ultimately reduce the amount of driving errors that can result in accidents – just by with the adaptation of road’s technical and planning standards to the needs of the driver. The experience shows that serious accidents can be prevented by a better orientation and optical guiding of the driver.

For instance in a very sharp accident curve with many fatal accidents one accident commission in Germany decided to to try a very innovative countermeasure: Instead of setting more chevron signs and speed limits they used a 200 cm high optical framing in the curve.

Fig. 18: Before: course of the curve is discontinuously, drivers underestimate the radius. The Speed is to high, 4 fatal accidents/year [14]

Fig. 19: After: course of the curve is framed, the coloured frame guides the driver and reduces speed [14]

Fig. 20: Speed before and after construction af an optical guiding frame in an accident curve in Germany [14]





The level and statistical spread of speed before and after the countermeasure show a very clear reduction of v85 from 61-65km/h to 46-50km/h – a reduction of 15km/h at all. The results are statistically significant (level of significance = 0,05).

These results are a strong indicator for a sustainable integration of the Human Factors concept in road planning, construction and maintenance. They make it mandatory to take into consideration the laws of driver’s space perception, information processing, act regulation and decision making when roads are planned and constructed. Safety engineers and road authorities can use the basic Human Factors demands of space perception for a new approach in judgement of accident causes. Road constructors can use it to qualify their planning process. The possibilities are various and promising.

REFERENCES

Literature

Birth, S., Sieber, G. (2004). Human Factors Guideline. Ministry of Infrastructure and

Regional Development. Brandenburg [1]

Cohen, A. S.; Zwahlen, H.T. (1989). Blicktechnik in Kurven. Wissenschaftliches

Gutachten. Schweizerische Gesellschaft für Unfallverhütung, bfu-report 13[2]

Otten, N.; Schroiff, H.-W. (1988). Untersuchungen zu Determinanten der

Geschwindigkeitswahl. Bericht zum Forschungsprojekt 8525/2 der Bundesanstalt für

Straßenwesen, Bereich Unfallforschung, Nr. 169[3]

Lozano, E. E. (1988). Visual needs in urban environments and physical planning. In:

J.L. Nasar (Ed.). Environmental Aesthetics. Theory, research & applications.

Cambridge: Cambridge University Press[4]

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Richtlinien für die Anlage von Straßen (RAS-L) – Teil „Linienführung. Köln[5]

Birth, S., Staadt, H., Sporbeck, O. 2002. HVO. In: Ministry of Infrastructure and

Regional Development. Brandenburg: Guideline for optical orientation by planting[6]

Birth, S. (2001). Report “Human Factors Accident Profiling B1/Werder-Geltow”.

Ministry of Infrastructure and Regional Development. Brandenburg[7]

Birth, S. (2003). Report “Human Factors accident analysis B109/140”. Ministry of

Infrastructure and Regional Development, Brandenburg[8]

Birth, S., Pflaumbaum, M., Sieber, G. (2006). Intelligenz System Transfer: HF-Training

for Engineers[9]

Ranking for European Road Safety (RANKERS) Research Project funded under the

6th Framework Program of the European Community: “Behaviour setting elements of

road design – a way to self-explaining roads: Validation of the „IST-Checklist 2005“:

Project Report of Work Package 3: Expert Assistance for Safety Review of Rural and

Urban Roads (single carriageway roads). [10]

Birth, S. and Aubin, D. (2009). “Space Perception and Road Design for Vulnerable

Road Users (VRU)”, presentation of working group results for PIARC. Cape Town[11]

Birth, S. (2009). “Human Factors Design Features Supporting Space Perception“,

lecture for the training of accident commissions in Brandenburg, Germany.

Potsdam[12]





HF-Subgroup of TC1.1 Safer Road Infrastructure (2010). General Voting of the

Human Factors Audit of 10 international design standards. Unpublished working

document. [13]

Birth, S., Demgensky, B., Wähner,U. (2011). Accident Analysis and evaluation of

countermeasures in an accident curve with fatal accidents. Report for the accident

comission Märkisch Oderland. Germany. [14]

Documents

HF Guiding Principles in Road Design