Safety and the human factor in road design

Nr 82 ., 1983

ISSN 0347-6049 National Road & Traffic Research Institute ' S-581 01 Linköping ' SwedenStatens väg- och trafikinstitut (VTI) ! 581 01 Linköping *

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Paper presentedto the Vth IRF AfricanHighway Conference inLibrev1lle Gabon

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Nr 82 0 1983 Statens väg- och trafikinstitut (VTI) 0 581 01 Linköping

ISSN 0347-6049 National Road & Traffic Research Institute ' S-581 01 Linköping ' Sweden

Safety and the human factor in road

design

by Kåre Rumar

Paper presented to the Vth IRF African Highway Conference in Libreville, Gabon, 6 11 February 1983, arranged by the International Road Federation (IRF), Washing-ton D.C., U.S.A., and Geneva, Switzerland.

S UMMARY

Initially the four goals of the road traffic system (effec-tivity, economy, safety, environment) are discussed. It is described how the weights of these goals vary with the le vel of system development. The safety level in road traffic for these group of countries with different degree of moto rization is compared. It is argued that develOping count ries have special difficulties and problems.

But in most countries it is shown that the human factor is the weak link in the road traffic system. Within the human factor road user information acquisition and processing are especially crucial.

It is discussed how such limitations in human performance could be met and counteracted by consideration in road de-sign and other road measures.

SAFETY AND THE HUMAN FACTOR IN ROAD DESIGN DEVELOPMENT OF THE ROAD TRAFFIC SYSTEM

The main problem in the initial stage of motorization is to reach an acceptable level of effectivity. Economy is of course also important while safety and environment are se

condary. This is the childhood of motorization and it is

illustrated in figure l.

Effectivity is the main important problem in many developing countries. In developing countries traffic often increases

very quickly, since the construction problems of vehicles

and roads are already solved. The traffic increase of va rious reasons lead to high accident levels.Therefore, in the process of develOpment, the weight of safety increases.

Of course effectivity and economy are still very important.

Often it even happens that safety is given priority because many accidents lower effectivity and increase costs con siderably.

In the final stage of traffic develOpment the weight of

environmental aspects is increased. But by then it is

rather difficult to change the basic characteristics of the traffic system.

One aim for developing countries should be to try to move up the goals of safety and environment and to put more em phasis on them at earlier stages of traffic development than is now done. Early preventive measures are much more effective and less expensive than late countermeasures.

SAFETY LEVELS AND TRENDS

In table 1 an effort is made to compare the safety level between countries at three separate developing stages of

motorization (IRF 1980). Three types of risk measures are compared. The only measure that takes exposure into account

is "killed per 100 milj vehicle km". But the exposure figu

res for most countries are so unreliable that the measure is dubious for general comparisons. Therefore the two other risk measures are presented. Except for the unreliability of the basic figure "number of killed persons" (due to dif ferences in definition, reporting rate etc.) the two mea sures of "killed per 100 000 persons" and "killed per

100 000 four wheel motor vehicles" are relatively reliable. The "killed per person" indicates the risk for every person

while the "killed per vehicle" indicates the risk in re lation to the number of vehicles. The later measure, in

fact, gives a fair indication of the safety level of the

traffic system.

The table shows that the personal risk is related to level of traffic development so that the higher the development

the higher the risk. The differences are however not very

another trend. The lower the motorization the higher the risk. And here the differences are dramatic about 1:5:10

100.

While the safety trend in the developed countries over the

last years is almost generally pointing in the right direc

tion (increased safety) the trends in the developing

count-ries are with a few exceptions pointing in the wrong direc

tion (decreased safety).

SPECIAL SAFETY ASPECTS IN DEVELOPING COUNTRIES

Table 1 only shows the general differences between developed and developing countries quantitative differences. But there are also several qualitative differences that are important to remember.

To begin with the proportion between protected and unpro tected road users are quite different. In developing count ries the pedestrians, cyclists, mOpedists, motorcyclists constitute a vast majority and will do so for many years to come. It is therefore not surprising that these cathe gories especially the pedestrians who often constitute

about half of the victims - dominate the injury and fatal

traffic accident victims. But there is normally a motor vehicle involved in the accident.

Another difference exists in quality and maintenance of roads and vehicles. This in turn is normally due to econo

mical and educational difficulties in developing countries. It is hard to raise the funds and find the skilled people necessary to build and maintain roads and vehicles.

The education system and level is often not of the same quality in deve10ping countries. It is hard to inform, educate and train verious types of road users.

Finally the information systems and research relevant for

road safety are of course not of the same quality in de veloping countries as in developed countries. It is dif ficult to get a clear picture of the safety situation, to follow up the effects of various actions, to develope countermeasures tailor made for the country and the situa tion in question.

ACCIDENT CAUSES

The normal analysis of a road traffic accident is the police

investigation. The aim of this investigation, however, is

not to find the real cause but to find who has broken the law and consequently will have to take the blame.

In order to find more unbiased causes other branches of transport (e.g. aviation, marine) have for many years made use of special accident analysis groups consisting of va rious specialists such as pilots, captains, engineers,

Therefore it is quite natural that efforts have been made to use the same technique on road traffic accidents.

A study by Sabey & Staughton (1975) and a study by Treat (1980) are two illustrative examples. In both studies a statistical and to some extent a clinical case study app

roach carried out by multidisciplinary teams was used.

Figure 2 shows the main results.

As can be seen these two completely separate rather large studies of several thousand accidents are almost unanimous in their pointing at the road user - the human factor as the dominating cause of road traffic accidents. The ana lyses have been extended further by trying to classify the type of human errors involved. The results show that re cognition errors (perception, comprehension, delays and decision errors) predominate. These types of errors could be assembled under the heading of "inappropriate informa

tion acquisition and processing".

ROAD TRAFFIC A MAN MACHINE SYSTEM

Man has built ingenious equipments for comfortable trans port and advanced routes for moving around. Transportation

is done at high speeds, long distances, with heavy cargo, at all levels of illumination, and in most climatic con-ditions. But the human being is still much the same. The functioning of the road traffic system may be

illu-strated by Figure 3. The human being is collecting infor-mation about the road, the traffic conditions, other road users, his own vehicle by means of his senses mainly vi sion. This information is treated by the central nervous system (CNS) where estimations, predictions, and decisions are made. The decisions are carried out by the various mus cular systems we may look to the right, steer to the left, brake, etc. This action, in turn, changes the information

acquired in the next moment and so on ... The system is a

closed loop, it has feedback. Society tries to insure that

the level of road users, vehicles and roads exceeds some minimum acceptable limits. Of course this system and its

functioning are influenced by various extraneous agents. The human being is e.g. influenced by age, fatigue, alco hol, drugs on one side and laws, rules, enforcement on the other. The technical system also changes its charac teristics with age, general illumination, weather, etc. The

importance of information acquisition and processing is clearly illustrated in Figure 3.

INFORMATION ACQUISITION AND PROCESSING

A simple but useful definition of information is "reduction of uncertainty". This means that information is not some thing in the environment. It is in the road user the per-ception and experience take the form of information. What

is information to one road user, might not be information to another or what is information to one road user at a certain moment might not be information to the same road user at another moment. It is the perceived situation not the physical reality that determines behaviour!

This is of vital importance. Road and traffic engineers construct the physical traffic environment (road geometry, alignment, surface, delineation, road signs, traffic sig nals etc). Many engineers presume intuitively that the same environment is perceived identically by passing road users. This is not the case. Every individual road user selects his own information (Rumar 1982).

It is very often forgotten that among our driving popula tions about half have subnormal vision. In normal road traf

fic, however, the perceptual problems are rather to select

the important information carrying stimuli from a complex array of stimuli (e.g. in most city situations). This se-lection and this analysis are influenced by higher order functions. Motivation and experience influence expectation and attention which in turn to a large extent control what is seen and heard (perceptual filtering). In the same way experience, knowledge, expectation influence the decoding of percepts and which decisions that are chosen (cognitive filtering).

COUNTERMEASURE PRINCIPLES

There are in principle three ways to improve the function ing of this system (see Figure 4).

These three types of countermeasures are of course already used today. But there seems to be a wide spread belief that

when a system is not functioning and if it mainly seems to

be due to human errors then it is the human component that should be changed (selection, improvement). Therefore, most efforts have been directed towards those measures. It is not until lately that it has become clear that the human component is often the most difficult one to change and to

modify. Therefore, the human characteristics should be the determining variable in the building of the system. Pre

viously, the road users were expected to adapt to the given road and vehiche characteristics. Now it is realised that man has several basic limitations which must be recognised and taken care of in the technical design or road geometry and surface, signs, signals, lighting, vehicles, etc. Of course, these limitations are important also for the design of education, training, information, etc.

THE HUMAN FACTOR IN ROAD DESIGN

The information from the road itself is given priority by most drivers (Rumar 1981). Consequently when we try to in fluence driver behaviour, road design could be a very eff ective area. There are many characteristics of road design

that could be discussed from a human factor point of view.

Let us for this purpose make a simple unorthodox classi

fication

(a) road alignment (horizontal and vertical curves)

(b) intersection design

(c) road width

(d) road surface (longitudinal and transversal, micro ,

macrotexture and unevenness, brightness, friction,

noise, material etc.).

Our knowledge concerning the relation between basic road design variables, human behaviour, and road safety is very limited and unsystematic. We know that these variables have effects but we do not know the causes of the effects.

Probably the most simple and straight forward requirement

concerning road alignment formulated so far is that "the road in front of the driver shall move in the picture plane"

(Dryselius, 1982). What is meant is that by giving the dri

vers various curves - the best one probably being an open S curve - we help the drivers to perceive correctly the course of the road, the distance to and speed of other road users. Vice versa the straight road is from this point of

View probably the worst road. It is very difficult to detect

lower hidden parts of the road, and to detect and to deter mine distance to and speed of other road users.

Furthermore the stimulus variation provided by a straight

road is low and required actions are few. The monotonous situation leeds to lowered levels of arousal the drivers are not prepared for action, should it be required. In night

traffic on flat straight roads drivers have to dip their

high beams on very long distances which leads to short vi-sible distances.

An ordinary four way intersection contains 32 potential conflict points between crossing, diverging and converging

traffic flows. Quite natural this means a difficult atten-tional and decisional task for the driver especially with

intensive and mixed traffic. One way of making the driver task more simple is to change an ordinary four way inter section to two three way intersections. Studies indicate that accidents are reduced by such modifications.

A modern way to try to lower speeds at special places with in built up areas is to decrease road width, to introduce

sharp curves, to build "humps", rumble strips, etc. These principles have been successfully used especially in the

Netherlands, Denmark and at some places in United Kingdom and Sweden. Road engineers often object strongly against "destroying" high quality roads that they have built. But this is a very narrow view. By showing the drivers very clearly, e.g. by the measures mentioned above, that the street is not an open thorough-fare but a place where other types of unprotected road users and children might appear

with high probability or a place where the quality of the road changes drasticially we can still permit cars in that area. The alternative is often to close the street or the road. What we try to do is to influence driver expectation and thereby also his attention and perception.

THE HUMAN FACTOR IN OTHER ROAD MEASURES

When we do not succeed in giving drivers full and correct information by natural means (road design) we have to apply other measures such as

(a) road markings

(b) roadside equipment (poles, trees, etc.) (c) road signs

(d) traffic signals

The road markings can be used in two ways to improve dri ver perception and expectation and to transmit some traffic law or rule to the driver. Examples of the first type are

the transversal stripes that have been successfully used in the United Kingdom at motorway exits where speeds tend to

be too high. The ordinary road central and edge lines also improve driver perception of the transversal position of the car and of vehicle speed. This is specially pronounced in night traffic with retroreflective markings. Here the visibility of the lines is so good that it might sometimes make drivers overconfident.

The markings can also to a limited extent be used to inform drivers of relevant rules e.g. overtaking prohibited, compulsory stop, yield information, stop prohibited, pe destrian priority etc.

The markings can be raised one step further to the side marker poles. These will function under most conditions and have proven to improve safety both day and night. Many of the measures mentioned so far work by improving driver per ception of speed, speed changes, distance and position. Present road signs have been shown not to work very well

(Johansson & Rumar, 1966). Road user information selection is normally rational. The items of information which are important to reach the goals are selected. Therefore, the motives are essential. The general motives are on the road transformed into applied motives. Of these applied motives the road information is primary, obstacles and other road users secondary, while the artificial information (e.g. signs) that is so common along our roads comes last. That is to say that the sign type of information is only picked up should there be time and opportunity. Also among this

third type of information a kind of hierarchic order exists;

some signs reduce uncertainty more than other signs. Relia-bility is a key concept for information systems.

Traffic signals are one way for the society to "take over"

driver tasks. They mean in essence that society has decided that the situation is so complicated and crowded that dri vers cannot make the right decisions - society does it for them. From an accident statistical point of view many stu dies in Sweden and Norway show that the introduction of traffic signals is effective especially at low speeds. They reduce the crossing accidents and the accidents with un protected road users but increase the rear end accidents.

EPILOGUE

Throughout this paper its argued that even if human errors dominate the causes to road traffic accidents, the acci dents are often caused by negligence in the traffic design phase to take into consideration human limitations to ac

quire and process information and to select and execute

decisions. It is argued that by basing the design of the road the road environment, vehicles, the signs, signals and regulations on human performance characteristics, human limitations, many human errors would be eliminated. This is an effective complimentary countermeasure to the more tra ditional ones selection of road users, improvement of road users.

REFERENCES

DRYSELIUS, B. (1982). Personal communication.

IRF (1980). World road statistics 1975 1979.

JOHANSSON, G. and RUMAR, K. (1966). Drivers and road signs. Ergonomics 9 (l), pp 57 62.

RUMAR, K. (1981). Impacts on road design of the human fac tor and information systems. International Road Federation IX Meeting. Stockholm. pp 31-50.

RUMAR,K. (1982). The human factor in road safety. Invited paper at the 11th ARRB meeting in Melbourne August 1982.

SABEY, B.E. and STAUGHTON, G.C. (1975). Interacting roles

of road environment, vehicle and road user in accidents. 5th International Conference of the International Associa tion for Accident and Traffic Medicine, London.

TREAT, J.R. (1980). A study of precrash factors involved in traffic accidents. Highway Safety Research Institute (HSRI). HSRI 10/11, 6/1. Ann Arbor, Michigan.

Author

Kåre Rumar Ph.D.

Professor, Research Director

National Swedish Road and Traffic Research Institute (VTI)

R i s k R i s k Ri s k C o u n t ry M o to r i z a t i o n ( K i l l e d ( K i l l e d ( K i l l e d (c ar s, t r u cks , p e r 10 0 00 0 p e r 1 0 0 00 0 p e r 1 0 0 m i l j bus e s p e r 1 0 0 p e r s ) f o u r w h ee l v e h ic l e km ) per s ) m o t o r v e h ic l e s ) I U S A 68 23 34 C a n a d a 53 22 34 Au s t r a l i a 49 23 42 Ne w Z e a l a n d 4 9 1 7 3 6 G e r ma n y (F RG ) 40 21 54 Fr a n c e 4 0 2 3 5 9 S w e d e n 37 11 27 G r e a t Br i t a i n 31 12 38 A V II G r e e c e 13 17 1 3 5 P o r t u g a l 11 21 1 8 0 H u n ga r y 10 16 1 52 II I T u ni s 14 41 1 Tu r k e y 10 42 8 T h a i l a n d 10 53 8 C o n g o 9 67 0 L e s o th o 1 1 1 3 0 0 M al i 4 1 3 3 0 Ni ge ri a 10 37 20 P a k i st a n 5 1 8 4 9 H omvoooxomm mmo m 0 N NNMMQ Q NN Brim N ,.... MhhmDOOM Q Q CDNCDMMN . MNr lr IOOOO Ta bl e 1 C o m p a r i s o n of pro b a b i l i t y of bein g ki ll ed (r isk) in a ro ad tr af fi c ac ci de nt de sc ri be d wi th th re e m ea s u r e s fo r t h r e e g r o u p s of c o u n t ri e s w i t h d i f -f e r e n t d e g r e e of m ot o r i z a t i o n (IRF 1 9 8 0 ) .

10

4 MOTORIZATION

(cars/100 persons)

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ROAD TRAFFIC AGE

Fig.1 The development of road traffic in three phases which have

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Fig.2 Percentage contributions to road accidents as received in a

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Fig.4 The three possible ways to improve system functioning in traffic, 1: Selection of road user (take away the bad ones) 2: Improvement

of road user performance (educate, inform, train, enforce road

users) 3: Adaptation of environment to road user characteristics

(make it easier to drive a car, a motorcycle, a moped, a bicycle, to walk).