to the optimal degree.
|
| One of life's challenges is to risk it to the optimal degree. |
With the help of Figure 4.1 the theory can now be spelled out in more precise detail insofar as it applies to traffic accidents. Although this figure has been drawn to be analogous to Figure 2.1, please note that Figure 4.1 does not refer to a single individual, but to all road users in a given jurisdiction such as a city, township, county, province or nation. Similarly, Box e (accident loss) refers to all traffic accidents that occur in the jurisdiction over a given period of time (say one year), and the extent of that loss is what the theory attempts to explain.
More precisely, the target level of accident risk is determined by four categories of motivating (i.e., subjective utility) factors:
The expression "target level of risk" should not be understood as implying that people strive for a certain level of risk for its own sake. Target risk does not mean risk for the sake of risk, just as the target temperature you set on your thermostat is not necessarily the one you would choose if energy costs were less important. Similarly, fever may well be useful in the body's fight against disease, but that does not mean that a fever is what you really want.
Figure 4.1: Homeostatic model relating the accident rate per head of population in a jurisdiction to the level of caution in road-user behaviour and vice versa, with the average target level of risk as the controlling variable.[1]
"Trip time is part of destination activity in some ways--[and] may be the source of various satisfactions: self-discovery, reflection, daydreams, reaching outside work and family context--we could list numerous examples which would clearly show that the minimization of distance covered or time spent is not what is sought--[but] pleasure in driving, speed, physical effort, a special relationship with the environment".[3]
A person's target level of traffic accident risk is defined as that level of subjective accident risk at which the difference between benefits and costs (including the perceived danger of accident) is believed to maximize. There may be cases in which risk is deliberately pursued, but most risks that people incur are rather more passively accepted as the inevitable consequence of their deliberate choice of action. Anybody who takes to the road knows that they might have an accident, either because of their own behaviour, or because of the behaviour of other road users that cannot be predicted, let alone controlled. Passive acceptance of risk is typical of travel by public means of transport. Anybody deciding to board an aircraft, train or bus as a passenger takes that risky decision before the act of boarding. That person has virtually no control over what will happen next. Thus, the subjective level of risk may be elected in the sense of being preferred or desired, but in other cases it may be better described as accepted or tolerated.
Figure 4.2: Theoretical representation of road users as net benefit maximizers and thus as risk optimizers. They choose an amount and manner of mobility such that the associated level of subjective risk corresponds with the point at which the expected net benefit is maximal. Note that the curve y3 has been drawn so that each y3 value equals the corresponding value y1 minus the corresponding value y2 absolute.[4]
For each speed and level of subjective accident risk, the expected net benefit equals the expected gain minus the expected loss. In Figure 4.2, the curves describing expected gain and expected loss have been drawn such that the expected net benefit curve rises from left to right, then reaches a top which is followed by a decline. At zero speed or zero subjective risk, there is no mobility and the net benefit of mobility is nil. When speed is extremely high, the expected loss is greater than the expected gain and the expected net benefit falls below zero.
The extremes are thus to be avoided: people should neither minimize nor maximize the danger of accident. What they should do instead is attempt to maximize the expected net benefit from road travel and choose a speed and other actions accordingly. They should try to select a level of risk that is above zero and that provides a maximal net benefit from the behaviours chosen. Risk homeostasis theory maintains that that is exactly what people are trying to do. Since zero risk is obviously not a meaningful goal, because there is no behaviour with total certainty of outcome, people target their risk level above zero.
Some of the variations in target risk between individuals are relatively long-lasting, for instance, those due to cultural values, the state of the economy, the socio-economic status of the person, incentives for accident-free driving, occupation, peer-group attitudes, level of education, gender, age and possibly personality traits. Shorter-term variations occur within the same individual and are due to the specific purpose of the trip and the urgency of arriving on time, current pre-occupations with stressing life events, mood, fatigue, being under the influence of alcohol, etc. Finally, some variations in target risk are momentary and may be incurred by the same person within the course of a trip. The target level rises after being held up in traffic and drops when making unexpectedly good progress, allowing the driver to relax. It has been shown that the longer drivers have to wait at a stop sign before entering a major street, the more they become willing to accept gaps in traffic that are shorter than those they rejected at first.[5] A sudden change in conditions such as a rain shower may increase the desire of pedestrians and bicyclists to reach their destination as quickly as possible if there is no shelter, thus increasing their target accident risk.
Variations in the target level of risk within the same person should not be viewed as a deficiency, let alone as a breakdown or absence of homeostatic control. As has been emphasized above, homeostasis does not mean invariance of the end result, but refers to a process that aims at insuring that the end result matches the set-point variable. When we have a fever, our body temperature is still homeostatically maintained. "The body's thermostat is simply set at a higher level."[6] The target temperature level is higher when people have a fever, just as the target blood pressure level is higher during heavy physical work than when people are resting.
In 1929, Walter Cannon,[7] an American physiologist, proposed the term "homeostasis" as a label for the dynamic process that had been discovered some 70 years earlier by the French physician Claude Bernard.[8] He showed considerable wisdom in calling it homeo-stasis, not iso-stasis. "Homeo" means "like, matching, agreeing" while "iso" means "same, equal, identical", as in isobar, isotope and isotherm. An isotherm is not a homeotherm, and isosceles is not homeosceles. Encyclopedias explain the difference between isostatic and homeostatic. Isostatic has to do with a state of sameness, homeostatic with a mechanism that keeps the output at a desired level. Homeostasis, therefore, should not be viewed as a process that keeps the output the same, at an invariably fixed level. As has been stressed by researchers at Harvard University another 70 years later:
Bernard's and Cannon's teachings that the integrity of higher forms of life relies on maintenance of a constant internal milieu have been central to modern physiological theory. Unfortunately, the teaching of [the concept of homeostasis] to successive generations of medical students has led to an overly simple perception being embedded in the collective medical consciousness. Cannon never suggested that every physiological variable is tightly regulated within limits, nor did he indicate that even the most well-regulated variables were maintained at an absolute constant level.
It is interesting to note that Cannon (1929), in the article in which he first outlined his concept of homeostasis, specifically pointed out that even the most tightly regulated variables may oscillate. He accordingly defined homeostasis as the process which regulates a physiological variable within certain limits, but that the variable may oscillate between those limits, and the limits themselves may change in response to some special demand.[9]
The "overly simple perception", alas, is not limited to people in the medical profession. Some researchers and practitioners in the field of safety and public health seem to suffer from the same affliction.
You may have noticed that I belabour the point that the target level of risk is not fixed once and forever--nor is the accident rate per capita. But I think there are good grounds for reiterating this point. The fact is that some published critiques of risk homeostasis theory have mistakenly interpreted it as stating that the target level of risk, and thus the accident loss, is immutably fixed.[10,11] This misinterpretation explains why one critic made the rather amusing, but no less erroneous, quip by referring to the theory as "the law of the conservation of misery". Risk homeostasis does not imply a law of "the conservation of accidents",[12] just as homeostasis of body temperature or blood pressure does not imply invariant body temperature or invariant blood pressure.
Homeostasis is a process, not an outcome, let alone an invariant outcome. Expressions such as "partial homeostasis", "exact homeostasis",[13] "incomplete homeostasis" and similar ones that have cropped up in a dozen or so years of "the great risk homeostasis debate" make very little sense. The use of such expressions betrays two basic misunderstandings of the nature of homeostasis. For one thing, these expressions are mistaken because they refer to outcome, not to process. For another, they misinterpret the outcome as something that should be fixed and invariant. Some people have referred to risk homeostasis theory saying that it implies constancy of risk.[14,15,16] They've even mislabelled it "the constant risk hypothesis".[17] We will see, in Chapter 11, that the main hope for developing interventions that are capable of reducing the accident loss per person is precisely located in the very pliability of the target level of risk.
The level of traffic accident risk that is perceived by the individual person at any moment of time derives from three sources: the person's past experience with traffic, the person's assessment of the accident potential of the immediate situation, and the degree of confidence the person has in possessing the necessary decision-making and vehicle-handling skill to cope with the situation.
The person's past experience embraces a vast variety of earlier events: personal fear-arousing occurrences, traffic conflicts, near-accidents, close calls, narrow escapes, witnessing other people's accidents, conversations with others about accidents, exposure to accident reports and occasional statistics in the mass media. These experiences leave the driver with a general impression of the degree of riskiness of the road. As these occurrences are commonplace and correlated with the accident statistics as gathered by police forces and governments, there is no need to assume that, for homeostasis to occur, people have more than a very dim knowledge of the official statistics.
The immediate situation includes the physical features of the road environment (weather, geometry, signs and signals), the driver's own speed and direction, and the paths and speeds of other road users. People read the risk implications of these features.
Finally, the perceived level of risk will be relatively low if the person is confident about having the necessary coping skills, and higher in the case of persons who doubt their abilities.
Some of these corrective actions have immediate effects only, while the effects of others are of a longer-term nature. The decisions having short-term effects upon safety include changing one's pathway, speed, following distance or trajectory; signalling to other road users; buckling or unbuckling the seatbelt; turning the vehicle lights on or off; increasing or decreasing one's mental effort in the driving task; concentration on particulars and general vigilance. The choice of vehicle or transportation mode--e.g., private car versus the bus or train--or of deciding to make a particular trip or not, are examples of longer-term decisions. The choice that is made is the one the person believes will best serve the maximization of her or his overall benefit.
Subsequently, this loss, along with the everyday experiences of accident risk that are associated with it (fear-provoking events, near-accidents, conversations about accidents, exposure to mass-media accident reports, and so forth), influence the level of risk as perceived by the surviving road users in the jurisdiction, that is, those who have not had a fatal accident (Box b). Thus, as long as the target level of risk (Box a) remains unaltered, accident loss at one point in time (Box e) and the degree of subsequent caution (Box c) displayed in road-user behaviour are related to each other in a mutually compensatory process that unfolds over time.
The first implication of this reasoning is that, at any point in time where the past accident rate is lower than the level of risk that people are willing to accept, road users will subsequently adopt a riskier manner and/or amount of mobility. The second implication is that they will do the opposite when the past record, and the personal experience associated with it, exceeds the preferred or target level of accident risk.
The first of these implications of risk homeostasis theory provides an explanation for what happened in Sweden and Iceland when these countries changed from left-hand to right-hand traffic at an early morning hour in the late 1960s. To the great surprise of many--including experts, laymen and politicians in Sweden and Iceland--the traffic accident rate per head of population dropped immediately and considerably after the change-over, but it subsequently returned to pre-existing trends, within two years in Sweden and, in Iceland, after about ten weeks.[19]
According to risk homeostasis theory, these findings may be explained as follows. Because of the change-over's major impact and fear-arousing interference with existing skills and habits, road users in these countries at first overestimated the level of accident risk that it would create. The thought of having to get up the following morning and drive on the opposite side of the road made drivers very apprehensive. Some road safety experts expected disastrous consequences.
Thus, the perceived level of risk surged to an unusual level that far exceeded the target level of risk. As a result, Swedish road users took unusually cautious adjustment actions, which in turn caused an unusual dip in the accident rate. During the 12-month period after the change-over date there was a 17% reduction in the number of traffic fatalities as compared to the preceding 12 months. After some time, however, the Swedes discovered, through their individual experiences and reports in the news media, that the new situation was not as dangerous as they had thought. The perceived level of risk went down, coming closer and closer again to the target level of risk. Consequently, the perceived need for prudent adjustment declined, cautious actions became less prevalent, and the accident rate returned to normal.
Jocular minds in the area of road safety have suggested that we should have such change-overs on a regular basis, say, every two or three years, in all countries. According to one of their jokes, the government of a particularly dumb country--or a particularly dumb government of any country (please fill in your favourite target)--planned to do exactly that. But, realizing that this would meet with considerable public opposition, this government decided to introduce the change-over in a gradual manner: in the first few weeks it would apply to trucks and buses only.
The difference between Sweden and Iceland in the time it took for the per capita accident rate to return to normal may be explained by reference to Symbol f in Figure 4.1. The time lag, assuming that all other influencing factors are equal, would be expected to be longer to the extent that the population is larger. As compared to Iceland, Sweden had approximately forty times more inhabitants at the time of the change-over to right-hand traffic.
Decision-making skill (Box 2) refers to the operator's ability to decide what she or he should do in order to produce the desired adjustment (Box c) so that the difference between the target and the perceived level of risk is minimized, that is, [a-b] equals about zero. It then depends upon the person's vehicle-handling skill (Box 3) as to how effectively he or she can carry out that decision.
The level of performance in any task can be improved by two contrasting methods: fitting the operator to the task, and/or fitting the task to the operator. The first can be achieved by providing good training procedures, by repeated practice on the task, and by providing people with knowledge of their level of performance. The second can be achieved by creating a work station and a physical work environment that enable the operator to perform the task at a more efficient level. Thus, the level of skilful driving performance can be improved by proper driver education on the one hand, and, on the other, by an ergonomically designed human-made environment, including controls and displays in vehicle design, and road geometry, signs, and signals in the traffic environment that reduce human error.
Many of these interventions, however, are unlikely to have a lasting effect upon the traffic accident loss, and only those that affect the target level of risk in the population can definitely achieve this. Why should this be so?
If I have been clear in what I have written so far, you already will have guessed the answer and realize that it is a simple one: the road users' task, as they see it and as it is performed by them, is not to minimize accident risk, but to maintain it at a level that is in keeping with their target level of risk, that is, their optimal level of risk. They attempt to maintain their target level of risk in order to maximize the overall benefit they can reap from their mode and manner of mobility. They act in accordance with what is reflected in popular sayings such as "nothing ventured, nothing gained", "no pain, no gain", "no guts, no glory", "nul culot, nul héro" and "la fortune sourit aux audacieux". The desire to maximize overall benefit offers strong motivation toward improvement of one's skills. The better one's skills, the more one is able to choose actions that agree with one's target level of risk.
As skills serve not to minimize risk, but to optimize it, the three types of skill are all located outside the closed loop in Figure 4.1, just as their thermostatic counterparts are in Figure 2.1. Thus, raising the level of these skills (Boxes 2, 3 and 4) for people in the same nation should not be expected to influence that nation's accident loss per head of population, although, for the individuals in that nation, individual differences in skill may matter a great deal to the likelihood of their personal survival.
Consider an imaginary education programme that produces population-wide improvements in risk perception, and the effects this would have. There would be a decrease in risk for the underestimators and an increase for the overestimators.
The unquestionable benefit of such education towards more correct risk perception is that individual road users would become more sophisticated "risk managers". Each of us would be enabled to adjust our behaviour more closely to our target level of risk. Thus, some would acquire a better chance to survive because they no longer underestimate objective risk, while others would become more likely to be killed because they no longer overestimate objective risk.
Would the nation-wide accident loss be reduced by our imaginary education programme? It depends. It would be reduced if the average perceived level of risk in the population is currently lower than the objective level of risk--in other words, if cases of risk-underestimation currently outnumber cases of the risk-overestimation. Such a situation would be similar to the effect of faulty thermometers that consistently indicate temperatures that are lower than the true temperature, so that actual room temperatures are higher than desired.
So, a crucial question arises: do people generally underestimate objective accident risk? The studies reported in Sections 3.1 and 3.3 have shown that drivers agree reasonably well with one another in their judgements of comparative accident risk when operating their vehicles in different road sections. Moreover, their pooled or collective perception of subjective risk corresponds remarkably well with the objective accident risk per vehicle-kilometre in each section as calculated from accident records.
Figure 4.3: The individual's task is to rank the above geometric shapes according to their surface area.[21]
Thus, there is reason for believing that drivers collectively make quite accurate assessments of relative risk, but that does not eliminate the possibility that, as a group, they either over- or underestimate the objective level of risk of particular manoeuvres in particular road situations, or of road traffic in general.
The notion "objective level of risk" is more easily mentioned than measured. What is meant by this term is the amount of accident risk (probability times severity) associated with a particular behaviour by a particular driver on a particular road in the presence of other particular road users. It includes the risk implications of the driver's skill, his momentary perceptions, his mental alertness, the speed of his vehicle, the braking ability of the car, the likely actions of the other road users, and so forth.
Needless to say, at this level of specification it is impossible to quantitatively ascertain the objective level of risk. The notion makes sense in theory only. The notion of relative risk is less demanding; all that is needed is to establish whether a given manoeuvre by a given driver under given circumstances is more risky or less risky than some other manoeuvre under the same conditions, or the same manoeuvre under other conditions.
If you ask a sample of drivers how they rate their own quality as a driver, you will typically find that more than half of them say that they are better than the average driver.[25,26] This arithmetical absurdity has also been observed in numerous fields other than driving and is due to the fact that overconfidence is more frequent than underconfidence. People are more likely to have expectations that are unrealistically optimistic than unrealistically pessimistic.[27,28,29] It is thus possible that people more often than not underestimate the traffic accident risk they expose themselves to.
There are, however, two factors that should dampen any enthusiasm for our imaginary nation-wide programme to improve risk perception as a means towards per capita accident reduction. One of these has already been mentioned--the programme would lead to an increase in the accident risk of those individuals who used to overestimate it. The other is that individuals who overestimate their perceptions of mastery and of being in control are marked by greater happiness, persistence at tasks, and mental health, and they are ultimately more effective in their performance than those who don't. A degree of unrealistic optimism is characteristic of normal human thought. Not exaggerating one's mastery or chances of success is associated with low self-esteem and mental depression.[30 ]
Self-aggrandizement is justified, provided it is not excessive. A healthy dose of self-overestimation is healthy, not only for the individual in question, but also for others, because it appears to promote the ability to care for others and to help them, to facilitate social bonding, and thus ultimately foster a more benevolent and happier society. Who would, in the face of this, want to reduce average people's self-perceptions to what is mathematically correct? It would also be a very difficult task, in part because the objective risk is not known. Only fatal accidents are relatively faithfully recorded; the accident costs in the form of physical injury and material damage are not reliably recorded. Fortunately, however, improvement in risk perception is not necessary if one wishes to reduce the accident loss per head of population, as will be seen in Chapter 11.
Such fluctuations in an individual's level of cautiousness following a lucky or unlucky experience can easily be demonstrated in the laboratory, as will be seen in Chapter 10. On the aggregate level, dips in accident rates are expected to occur if road users collectively perceive a sudden increase in accident potential, as was the case when Sweden (in 1967) and Iceland (in 1968) changed over from left-hand traffic to right-hand traffic.19 Likewise, there are indications that major aviation accidents are followed by periods in which fewer people decide to fly.[31] Usually, however, fluctuations in caution and imprudence in different individuals would be out of phase with one another, and the temporal fluctuations of the accident rate of the collective would thus be flattened out.
Another dampening factor is the human ability to anticipate change in "intrinsic risk". Suppose, for example, that a highway is upgraded from two lanes to four. This signifies a reduction in intrinsic risk, and if drivers were to maintain the same behaviour (speeds, levels of alertness, etc.), the accident rate per hour of driving on that highway would decrease. But people may be able to anticipate the change in intrinsic risk and to modify their behaviour accordingly. This is "feed-forward adaptation",[32] as distinct from adjustment following feedback. Thus, behavioural compensation may occur in response to the introduction of non-motivational accident counter-measures (those that do not affect the willingness to take risk) before a change in accident rate has an opportunity to occur. In fact, the anticipatory compensation prevents just that.
Homeostasis is supposed to take place through the actions of individual human beings, not on the level of the human collective in some mysterious or metaphysical manner. Although the accident loss per capita characterizes a collective and is often remarkably stable from year to year, this does not imply some decision-making process on a supra-individual level. The accident loss is the sum total of the separate consequences of individual actions.
According to the theory, individual road users try to keep their accident risk per time unit of exposure in equilibrium with their prevailing target level of risk. As the target level of risk is greater than zero, the individual runs an inevitable risk of accident. If the accident happens and it is fatal, the individual can no longer make any subsequent adjustment actions, but the individuals in the population of survivors can. Each accident that happens adds an increment to the perceived level of accident risk.
Suppose now that, on average across individuals, the target level of risk corresponds in reality with one fatal accident per two million hours of exposure to road traffic. Suppose, too, that the individuals spend, on average, 400 hours per year in road traffic.[33] Consequently, there would be one fatality per 2 x 106/400 = 5000 person-years of life. In the course of one calendar year, therefore, about 106/5000 = 200 individuals would be expected to be killed on the roads in a jurisdiction of one million inhabitants.
The surviving members of the population become aware, in a general and quantitatively diffuse way, by virtue of their everyday experiences on the roads and conversations with others, as well as through accident reports in the media. These experiences influence the level of accident risk perceived by road users who have had no fatal accident, and thus influence their subsequent behaviour. A ship stranded on the beach is a beacon for those at sea. The deaths of some is a warning to others to be more careful. People typically learn, not only from their own mistakes, but also from mistakes made by others: one person's fault is somebody else's lesson. People typically learn from their own successes and also from the successes of others. This is how the accident loss in a population can be maintained at a more or less stable level over time.
If one looks up at a flock of birds turning in flight, or down from a tall tower at the traffic movements below, the collective action sometimes appears as if it were guided by an "invisible hand". The illusion is created by the smooth coordination of individual decisions, the individuals (birds or drivers) each finely tuning their actions to the actions of other individuals. Continuity over time is similarly achieved.
It should be emphasized that this theory attempts to explain the accident rate per head of population, not the occurrence of specific individual accidents, nor their immediate and material causes, such as errors of perception, decision or execution. The occurrence of these errors is viewed as the consequence of the extent to which people allow themselves or others to make such errors, and of the fact that they expose themselves to dangerous conditions, including malfunctioning equipment. The specific errors leading to specific accidents may be interesting, but they have no bearing on the rate of accidents. The error rate is viewed as a direct consequence of the accepted level of risk. The identification of specific errors may help avoid specific types of accidents in the future, but this does not mean that the future accident rate will be favourably affected. The elimination of specific errors does not imply a commensurate reduction in the overall rate of errors, nor a commensurate reduction in the accident rate. We may recall the delta fallacy that was mentioned in the Introduction: successive damming of the channels in the delta will reduce or even eliminate the flow of water through these channels, but the total amount of water running to the sea is not reduced.
Most people who settle or live in flood-prone or quake-prone areas do so knowingly and accept the risk in return for the fertility of the land. People know that driving or flying carries a risk of accident. The theory does not deal with the rare and presumably totally unforeseeable events that go under the poetic name of "acts of God". People's risk acceptance is viewed as the underlying cause, the root cause--the "causa causans"--of the accident rate per head of population.
From what has been said so far about risk homeostasis theory, it is clear that the human being is seen as a strategist, a planner, who attempts to optimize, not minimize, the level of risk-taking for the purpose of maximizing the benefits--economic, biological and psychological--that may be derived from life.
The human being is not perceived as a robot with a conditioning history, a robot that needs some additional conditioning for the accidents to go away. Such a view would suggest that what is needed to reduce the accident rate is more road user training, including driver training.
The human being is not perceived as a haphazard bundle of poorly controlled emotions that can erupt at any time, and needs the disciplining force of a paternalistic authority to be kept in check. This view would inspire accident countermeasures that take the form of legislation against specific unsafe acts, and the enforcement of such legislation.
The human being is not perceived as a less than perfect automaton with a few loose nuts and bolts that will function more safely if its environment is made more forgiving. According to that view, accidents can be reduced by better engineering and more sophisticated ergonomics of the hardware of roads and vehicles.
Instead, the human being is being viewed as a being that, if motivated by accident countermeasures to act more safely, will do so, and the accident rate per head of population will go down.
Yet, on repeated occasions, the theory has been charged with casting a pessimistic perspective on the potential for traffic accident prevention.[34,35] Hence the reference to it as "Wilde's law of the conservation of accidents"12, or "the principle of the preservation of the accident rate".[12] Nothing could be farther from what I intended. What the theory does is to stress the resilience, ingenuity, adaptability and resourcefulness of human beings under changing environmental conditions, including those of their own collective making. It would be saddening indeed if people showed no inclination to search for behaviour alternatives when confronted with changing technological conditions that provide them with new opportunities to behave in productive ways, without altering their degree of willingness to take risks of their own choice. There would be cause for pessimism about the human condition if the accident rate per time unit of exposure or per capita went down as a result of interventions that do not affect the amount of risk people are willing to take.
Suppose a "Mr. X" has decided on the value of his life, and thus, on the extent to which he is willing to risk it. He tries to obtain a maximum quality and quantity of mobility in return for this sacrifice he is willing to make. Now provide this person with a seatbelt, wider lanes, better brakes or whatever intervention that can make driving intrinsically safer--that is, safer provided no change in behaviour occurred. Mr. X has the choice of responding to this intervention with or without changing his behaviour. If he does change his behaviour, he can obtain an even higher quality and quantity of mobility. If he does not change it, he no longer obtains the maximum benefit in return for what he is willing to sacrifice. That's dumb, and if people typically reacted in this fashion, there would be serious cause for a pessimistic view of their ability to utilize new opportunities.
For safety interventions to be effective in reducing the accident rate per head of population, these interventions have to reduce people's willingness to risk their lives. Chapter 11 describes methods for this purpose and the results obtained with these methods. It will be seen that the art of effective safety management is the art of reducing the target level of risk. The fact that the target level of risk is modifiable is sufficient reason for debunking the myth that the theory of risk homeostasis is pessimistic and that accident rates cannot be reduced.
Instead of motivating people towards greater safety, one could, as some have suggested, attempt to interfere with the "natural unfolding" of the homeostatic dynamic (presuming that this dynamic explains what is going on). Roads might be designed such that curves appear to be more dangerous than they are. Driver training might teach students that certain manoeuvres are more dangerous than they are. One might introduce invisible safety features in cars, such as collapsible steering columns, padded dashboards and reinforced doors. The feedback loop from accidents to accident risk perception (see Figure 4.1) might be distorted by mass media propaganda that tells people that the roads are more dangerous than they are.
Apart from being distasteful to a society that values full disclosure of the facts and ready access to information (called "glasnost" in Moscow and Irkutsk) any such attempts to instill a false sense of insecurity are unlikely to be effective in the long run. People will eventually find out. One can fool some of the people some of the time, but not all of the people all the time, as one president of the USA has said. Moreover, when a policy of deception is pursued, the authorities will eventually lose credibility and respect when people find out, and this may have various kinds of repercussions that are counterproductive to a healthy functioning of society. Secrecy and deception will come home to roost.
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