David C Stark Traffic Safety Research Innovations Ltd

Transcription

1 THE EFFECTS OF LOWERING THE UK LEGAL LIMIT FOR DRINK DRIVING David C Stark Traffic Safety Research Innovations Ltd 1. INTRODUCTION The safety implications of drinking and driving have been well understood for some considerable time, and over the past two decades the Home Office and Department of Transport have campaigned strongly to publicise the risks involved and change peoples' perceptions of the social acceptability of drink driving. Although the legal limit has remained the same - a blood alcohol content (BAC) of 80 mg/100ml - over this period, penalties for drink driving offences have been increased and the roadside breath testing of accident involved drivers has become a routine matter. This effort has been underpinned by a considerable body of research on the effects of drink drive legislation and its enforcement, as well as the psychological factors involved in drink driving and rehabilitation of offenders. The quantitative relations between alcohol and accident risk have also been studied in some depth. As a result, the occurrence of alcohol as a factor in road accidents, and especially fatal accidents, has declined dramatically. This is very gratifying, especially when one considers the long period over which little progress seemed to be made. But there is more that can still be achieved, so it is essential that we should have a good understanding of the current scale of the problem in the UK and the means at our disposal for reducing it. The UK has already achieved considerable success in tackling drink driving, so the measures that might be appropriate in countries with high levels of drink driving may no longer be relevant. For example, considerable success with random breath testing - supported by other measures of course - has been reported in Australia, but it is important to realise that the average level of blood alcohol among drink drivers in the states that adopted this approach still almost twice as high as in the UK. A growing number of countries have lower drink drive limits of zero or 50 m#i00ml, though this does not necessarily mean that they have lower levels of drink driving than in the UK. On the other hand, while DOT publicity has emphasised the tragedy of the injuries and deaths of the innocent victims of drink driving accidents, other countries have moved ahead on a wider front in defining more closely the responsibility of drivers who kill and maim vulnerable road users. We might also consider the very rapid changes in car ownership and use that have taken place over the period and in particular the increase in the numbers of more socially responsible drivers, especially among the young or female drivers, who are prepared forego alcohol when they are driving. It is timely then to take a closer, more quantitative look at the situation in the UK, with the aim of reviewing the information available on drink driving and its associated risk, seeing what changes have been taking place in the levels of drink drive enforcement and assess its effectiveness. Then we might be able to come to a better informed view as to the likely effects of changes in the legal limit. 331

2 2. W H A T A R E T H E R I S K S? Before going into the statistical considerations, it is important to realise that while drink driving in excess of the legal limit can be extremely dangerous, the chance of an accident may still be sufficiently small that individual drivers have no reliable means of assessing just how unsafe their behaviour might be. Most people significantly under-estimate the amount of alcohol that needs to be consumed to take a driver over the limit, so much of their 'experience' may actually be based on alcohol levels well below the legal limit. Consider for example a driver who is well over the limit driving 5 miles back from the pub one evening. The injury accident rate for travel at night is perhaps 2 per million miles driven, so even if alcohol related factors increase accident risk 10 fold there is only a probability of one in a 10 thousand of an accident - not a fatal accident even - so the opportunity to revise the view that the risk is acceptable will very rarely occur: perhaps not even once in a lifetime. These issues were raised by the UK Department of Health last year, in an attempt to provide doctors and patients with a better understanding of medical risks, and to try to get across the idea that 'safe' means a low risk of harm rather than a complete absence of danger. "If the word 'safe' is to be used it must be seen to mean negligible, but should not imply zero, risk." (Caiman, 1996). White the effort is commendable it offers considerable difficulties for road safety practitioners, as can be seen from the table below which has been adapted from the DOH guidelines to terminolog3r. Table 1. DOH Terminology of Risk Annual Risk of Dying Odds against Descrip.tion Example greater than 100:1 High N/A 100:1-1000:1 Moderate 200: 1; smoking 10 cigarettes a day 1000:1-10,000:1 Low 8000:1; road accident 10,000:1-100,00:1 Very Low 12,000:1; leukaemia 1DO,DI30:I - 1 mil~ion:l Min'~ma~ 50,0~301; ra'fiway accitlem less than 1 million: 1 Negligible 10 million :1; lightning strike This recommendation lacks any good examples of high risk situations that have a continuous effect on the population at large. In fact activities that pose annual odds of being killed of 10:1 or greater can only really be described as lethal, in that hardly anyone exposed to this level of hazard would live long enough to reach adulthood. The odds against being killed in a road accident are described as Iow, verging on very low, which sounds reasonable until one considers that if people were to start driving around with blood alcohol levels of twice the legal limit this only would increase the risk to moderate, still less than smoking 10 cigarettes a day. On the other hand, while the odds of being killed by lightning may be negligible, there are situations, such as being in a thunderstorm on the top of a mountain, which are extremely risky and call for prompt action to get out of danger. What we need to do then is shift the terms of 332

3 description down one level. Driving is moderately dangerous, and drink driving is highly dangerous. So for that matter is riding a bicycle, but the roads would be much safer if everyone cycled, which is not something you might say about drink driving. What is required is the perspective that table 2 provides, where we consider the increase in risk in the context of traffic safety and accident reduction measures. Table 2. Factors Affecting Traffic Safety Doubling/Halving of Risk: Driving at Legal Limit 4- speeds of 5-10 mph above limit in towns driving at night traffic calming pedestrian crossings Tenfold Increase/Decrease: Driving at Twice Legal Limit 4- speeds of mph above limit in towns cyclists, motorcyclists, child pedestrians third world vs developed world motorways vs urban roads The main thrust of DOT publicity has been to encourage the belief that all drink driving carries an unacceptable level of risk. What has not been stressed is just how rapidly driving performance deteriorates at alcohol levels above the legal limit. Some insight may be obtained from less specific studies of alcohol impairment, (Rabbit, 1993) where there is clear evidence of its effect in increasing reaction time and hazard perception time, but this has not been correlated with changes in driving bebaviour. What we know about the effect of alcohol on accident risk for car drivers can be summed up very simply: I. There is no evidence of any increase in risk up to a BAC of Risk increases very rapidly, exponentially thereat~er up to a BAC of about 300 where other factors start to intervene eg falling asleep. 3. The risk of an accident doubles at BAC 80, the legal limit, and increases by a factor of five or so for each BAC increase of S0 thereafter. 4. For younger or inexperienced drivers the rate of increase can be much higher. 5. The risk of being killed increases in line with injury accidents up to BAC of 150, but perhaps twice as rapidly thereafter. 6. The effect of BAC on risk is twice as great for single vehicle accidents, particularly those that occur while negotiating turns at bends or junctions. 333

4 The key empirical study of accident risk was made in the USA by Borkenstein in The University of Indiana carded out a study in Grand Rapids which compared accident involved drivers with a closely matched control group. This enabled them to investigate a number of variables affecting accident risk and provided the statistical distributions of blood alcohol, which allowed graphs of incremental risk associated with different levels of alcohol to be calculated. This study provided the first appreciation than alcohol has relatively little affect on risk at low levels, but thereafter its effect increases very rapidly. (Allsop, 1966) The main shott-coming of this type of study that there is not enough information for high BAC levels. This can, however, be obtained from an analysis of records of drink drive prosecutions, and some work (Broughton,1986), (Stark, t986) on these data was carded out by TRL about ten years ago which yielded reliable models of the distribution of alcohol levels in accident involved and non-involved drivers as well as the risk factors. The risk of a fatal accident has been shown to increase more rapidly with BAC than for other injury categories. One of the reasons for this is that the injured party's chances of recovery are adversely affected by the alcohol consumed (Evans, 1993 ), (Jurkovich,1993), but there may be other factors, such as failure to take action that might mitigate the severity of the crash or driving at high speed, particularly on rural roads. While alcohol appears to have little effect on driving safety below BAC 40, the risk for drinking pedestrians (Stark, 1987) does increase rapidly even at low levels. So this is more likely to reflect the differences between the tasks faced by drivers and pedestrians and there is probably a greater amount of slack in driving which is not immediately taken up at lower levels of alcohol impairment. Our knowledge is weakest on the key issue of the range of individual risk, except in that it is known to vary geatly. It is in fact very difficult to conduct such studies with realistic driving tasks though the will to carry out this work has also been lacking, partly because DOT has correctly resisted any suggestion that a 'good' driver might safely flout traffic laws. What is known about individual susceptibility can be readily summarised. There is a group clearly defined by age and experience, totalling for perhaps some 20% of drivers, who do not handle the effects of even moderate levels of alcohol well. This problem is exacerbated by the fact that they also have much higher accident rates in general. No comparable sub-groups who might perform much better than average have been identified, though one might suspect that alcoholics may have a much greater alcohol tolerance. While it is likely that the safer, more experienced drivers will perform better at a given BAC level, it will be seen later that they do tend to drink more overall. It should also be stressed that individual variation is large enough that some individuals in the high risk group are actually less susceptible to the effects of alcohol than some individuals in the lower risk group. While this information can be used in strategic studies by policy makers in predicting drink drive casualties, they do not provide such reliable information when we come to consider the role of alcohol as a causative factor in a specific accident. Not all driving tasks are affected in the same way and the Grand Rapids study demonstrated that the risk of a single vehicle accident increased much more rapidly than for two vehicle accidents. Analysis of UK breath test data has identified two accident types that account for this difference, namely single vehicle accidents while turning or negotiating bends. In both cases the failure to judge speed correctly is likely to have been a critical factor in losing control of the vehicle. For example, a driver breath tested after leaving the road on a bend is twice as likely to be over the legal limit as drivers involved in other types of accident. Hence it would be twice as likely that alcohol was a contributory factor to the accident. 334

5 What we should conclude then is that drink driving is one of the most important factors in increasing accident risk, and that the safety benefits from tackling it are as great as the best we might achieve from any other form of traffic safety management. 3. HOW SHOULD WE APPORTION BLAME? It is recognised that a driver's accident history provides reliable information about the individual. Insurance companies will rapidly revise their ideas about the premium that a driver should be paying, even on the basis of a damage only accident. The statistical methods for revising estimates of the driver's safety are straightforward (Stark, 1986) and it has been shown that there is considerable variation in individual risk. So this is not simply an academic exercise. We may start with the assurance that a driver is mature and has a lot of driving experience, but when we learn that this is not reflected in the safety record we should be inclined to revise that opinion quite rapidly. The evidence needs to be considered carefully, however, for in most two vehicle accidents we also need to apportion responsibility for the accident. For example in a rear shunt, it is the driver of the vehicle which drives into the rear of the other who is usually held responsible. It may be true that the accident would not have occurred if the vehicle in front had not been stationary or slow moving, in which case one might say that in a statistical sense this was the cause of the accident. The behaviour of the driver in the front vehicle may have been the primary cause of the accident, but the blame lies with the second driver who should have acted to prevent it. The same principles applies to drink driving accidents. After a drinking session drivers may believe that they are capable of driving safely and that successfully completing the trip provides some confirmation that this was a correct assessment. In fact the level of absolute risk is normally so small that not having an accident on that trip tells us very little about the driver's capability. Individuals who have had considerable experience of drinking and driving may still be very susceptible to the effects of alcohol in increasing accident risk. Returning to the example of the driver back from the pub, the I0 fold increase in risk might correspond to a BAC of twice the legal limit, so even at these very high alcohol levels there is only a very small probability that an opportunity to revise the view that the risk is acceptable will occur. If an accident does occur, however, it is very difficult to sustain the argument that the risk was not greatly increased on that trip. Either the driver was very unlucky - in a stronger sense than simply unfortunate - or the driving capability was considerably below par. The greater the level of blood alcohol, the more inclined we should be towards the latter explanation. There are two reasons why alcohol has a strong effect on accident risk. The first is impairment, the overall degradation of reaction time, motor skills and cognitive ability, which means that the driver is no longer capable of driving safely. The second factor is that drivers may no longer choose to drive safely. They may be lulled into the false belief that they are driving well. In particular, they may be inclined to drive a greater speeds than they would normally, which is only recently known to be responsible for a very marked increase in risk. When we come to consider the variation in alcohol induced risk between individuals, this will first depend on the level of impairment, which while it varies considerably between individuals is likely to be fairly steady over time. Remember we are not talking about alcohol consumption, which involves consideration of different rates of absorption, but blood alcohol levels. The effects on driving style will also vary among individuals but there are additional factors that give rise to a greater variability over time. For example, a passenger might insist that the driver slow down. What this means then is that we cannot simply assert that a driver 335

6 at twice the legal limit has a 10 fold increase in risk, or that where an accident has occurred that there is a 90% chance that the blood alcohol level was responsible for the accident. The statistical tool required for risk assessment after the event is Bayes Theorem, which provides us with the machinery for revising the probability of a particular risk level in the light of the accident circumstances. What we need to know is: 1. the type of accident 2. the BAC of the driver at the time of the accident 3. the distribution of increased risk factors that this BAC level implies across the range of individual susceptibilities. At present, we have do not have enough information about the range of individual variation to be able to make reliable calculations of risk distributions for low BAC levels, which includes the current UK legal limit, far less any lower limit. So if we want to make any attempt to quantify the process of apportioning blame at lower BAC levels then there is a need for further research. There is a lot more that can be said at higher BAC levels. A simple rule of thumb is that in the case of an accident involved driver at twice the legal limit there is a 90% chance of a risk factor of 10 or greater. This should be compared with an average risk factor of 10 for the prior risk assessment. At three times the legal limit the risk factor at the 90% confidence level is 50. In the case of a single vehicle losing control in a turn at a junctions or bend, the same risk factors apply at a confidence level of 95%. 4. HOW MUCH DRINK DRIVING IS THERE IN THE UK? The best means of obtaining information about BAC levels in motorists is by means of roadside breath test surveys. These are expensive and pose to a number of difficult problems in execution, so they are not common and no repetition of the Grand Rapids study has been made. There has only been one such study in the UK in recent years - or over a decade ago if you look at it that way - when TRL carried out a number of roadside surveys of motorists to obtain information on the distribution of alcohol levels in accident non-involved drivers in the UK (Sabey, 1988), (Everest, 1991). None of these surveys use any kind of statistical model for the analysis of the findings, so it is difficult to compare drink drive levels between different countries, or in the same country at different times. The present author made the first attempt at this while working on the effects of the 1983 drink-drive legislation (Stark, 1986) and the model developed has since proved to be robust. The aim is to identify three groups of drivers: those for whom drinldng has no association with their present trip: drivers who have been drinking in the past 12 hours or even earlier, but who have no significant level of blood alcohol remaining: drivers who have been drinking recently, with significant levels of alcohol present. The last group are the drink drivers, of whom only a small proportion, perhaps 10%, will be over the legal limit. The reason for distin~maishing between the first two groups is that drink drive le~slation and changes in levels of enforcement will have no bearing on the first set of drivers, but it will alter the balance between the second and third groups. If we confine our attention to these last two groups for the moment, then we can sum up the drink drive situation by two statistics, the proportion of drink drivers and the mean BAC level in this group. When we come to discuss the safety 336

7 implications of modifying drink drive behaviour it will be important to distinguish the types of change taking place. The proportion of drink drivers is somewhat difficult to estimate, though the 1987 UK surveys showed that about 14% of drivers tested in evening surveys could be classified in this group. The proportions in the remainder of the day will be much lower, perhaps 3-5%. The reason that we only need to know the mean BAC of drink drivers is that the statistical distribution of BAC levels is a negative exponential distribution, which only has one parameter, the mean. The technically minded will recognise this distribution as the maximum entropy distribution on the positive real line. What this means is that the distribution is devoid of any interesting features, so its shape is unaffected by the legal limit in force. This is in strong contrast to distributions of vehicle speeds which clearly reflect the level of compliance to the prevailing speed limit. There is very little information available about the BAC levels in drink drivers, but it is very interesting. Table 3 shows the results of breath tests - or estimates of equivalents - in five countries with a range of limits and levels of enforcement. Care should be taken in interpreting this table as the weighting imparted by the original sampling is very important. The dates of the surveys should also be noted, as there have been considerable reductions in drink driving, in the USA for example, over the past decade. Table 3. Mean BAC of Drink Drivers in Five Countries Legal Limit Country Sampling or Estimate: Random Date Mean BAC (mg/100ml) 100 USA $ 80 UK Australia Australia Netherlands Slovenia * * Sampling : Moving Traffic Offenders 80 UK Slovenia $ Sampling : Car Driver Fatalities 80 UK USA We might conclude then that while reducing the legal limit can reduce the mean BAC level, countries with a lower limit will not necessarily have lower mean BACs among drink drivers. The difference between levels of enforcement is probably much more important. The UK surveys in 1987 were disaggregated by age, so a direct comparison could be made with the BAC levels estimated from Home Office data on drink drive prosecutions in (Stark, 1986). This is shown in Table 4, along with the comparison between sexes from the 1987 surveys. There is little reduction between the 1983 and 1987 estimates of the means for different age groups, which is a point we will return to later. The differences by age and sex are very important though. What they reveal is that the groups with higher accident rates (per vehicle kilometre) have lower BACs, which suggests that they tend to modify their habits to compensate for the alcohol related increase in risk. "" 337

8 Table 4. Mean Drink Driver BAC by Age and Sex Male Female A simple, statistical model of the effects of enforcement on drivers' alcohol consumption can provide some guidance here. The basic model is that the preferred alcohol consumption, c, is given by: c = Max(kt-d,0)... 1 where k is the rate of alcohol consumption, t is the time the driver spends drinking and d is a deterrence factor that depends on the legal limit, level of enforcement etc. If t and d are sampled from negative exponential distributions with means T and D, then this model generates the two groups, drink drivers and those with no significant levels of blood alcohol. Alcohol consumption is distributed as a negative exponential, with mean C = kt. The BAC level in drivers who have been drinking is obtained after allowing for the alcohol metabolised: b = Max((k-m)t-d,0)...2 where m is the rate at which alcohol is metabolised. So b is distributed as a negative exponential, with mean B = (k-m)t. Note that the means of both alcohol consumption and BAC are independent of the deterrence, except through the variation o f k and T, so unless the effect of increased deterrence is to modify drink drivers' preferences and habits, it will have no effect on the mean BAC. This is very important, as we will see later. The average time spent drinking, which we can take as the time between the start of drinking and beginning to drive is given by: T d = T + D/k...3 which means that, other things being equal, people who like to drink quickly spend less time drinking and that the effect of increased deterrence is to increase the time interval between dnnkm~, and driving. One other useful prediction from the model is that the alcohol consumption of drivers who have been drinking but have no significant blood alcohol remaining is distributed as a negative exponential, with mean C O = mt. This allows the value o f t to be determined from surveys of alcohol consumption, although it Should be noted that drink drivers are prone to under-reporting of their drinking by a factor of two. The proportion of drink drivers is given by: (k-m)t Pd (k-m)t + D...4 which does vary directly with the level of deterrence. While this model refers to a single class of drink drivers, it is a simple matter to average over the whole population, obtaining identical equations with each parameter replaced by its mean value. 338

9 5. WHAT ARE THE TRENDS IN THE UK? A direct comparison on drink driver BACs between 1983 and 1987 gives no indication of any reduction over this admittedly short period. To obtain a longer period for comparison, we have to go to the results of breath tests applied by the police to drivers involved in accidents or moving traffic offences. Overall, the picture provided by the drink drive statistics is very encouraging. The proportion of car drivers involved in injury accidents or stopped by police for moving traffic offences who are over the legal limit has halved between 1983 and 1995, with a similar decline in the fatally injured. Over the same period car driver casualties increased by about 20%, so there has been a significant absolute reduction in drink driving. With motorcyclists the reduction has not been so marked, perhaps 15%. But the numbers of motorcycle casualties has fallen by 70%, with the reduction mainly among younger riders. So motorcycle riders now tend to be older, with higher levels of alcohol consumption, so the changes in the proportions of offending rider would not be as great. Over this period the penalties for drink driving have been made tougher and the number of breath test administered by the police has increased by a factor of 2.5, so the elasticity of the proportion of drink driving among car drivers with respect to enforcement with the legal limit fixed can be estimated: dlog(pd) dlog(e) The Coroners' database also provides some reliable information on the variation of BAC levels in fatally injured drivers. Analysis of this data suggests that the mean BAC &drink drivers has remained constant over the period, even increasing slightly for motorcyclists. What this means then is that falling numbers of drink drivers have been responsible for the accident reductions, a result which is somewhat unexpected. Most attempts to analyse drink driving have proceeded from the assumption that drivers modify their alcohol consumption to stay below the legal limit, despite the lack of empirical evidence of any such behaviour. On the other hand, considering the tow level of understanding of the subject that surveys have revealed among motorists one might well prefer the explanation that their only practical recourse is not to drink and drive. Drivers may come to adapt their drinking habits, but it looks as if- in the UK at least - this might be a long term process. A further round of UK breath test surveys would be timely then and it could shed considerable light on this point. 6. PREDICTING THE EFFECTS OF CHANGES IN THE LEGAL LIMIT. Studies of reductions in the drink drive limit, from 100 to 80 in the USA and 80 to 50 in Australia, show that reductions of about 15% in drink drive accidents can be obtained, and the setting of a much lower limit, zero or 20, for younger drivers in the USA has indicated a reduction of 20% or more. It is difficult to translate these results directly into UK practice, however, as the starting point may already be much lower. Analysis of the changes in BAC levels in Australia suggest that a significant drop in mean BAC took place, so there is also evidence that changes in drinking habits can be achieved in the short term. But we will assume that the main effects of changing the legal limit in the UK will be to change the frequency of drink driving, without changing its character. To predict the effects of changing the legal limit, L, rather than the level of enforcement, E, we need to know how the deterrence, D, depends each. This is most readily obtained from a model relating the preferred rate of alcohol consumption to the level of enforcement and the legal limit: 339

10 k0(1 + xl) + yme k ~ l + x L + y E...6 Calibration of this model for UK conditions gives: dlog(k) dlog(k) , -... dlogoe) dlog(l) = which means that with a legal limit of 80, a 1% increase in enforcement has a 50% greater effect on the deterrence than a 1% reduction in the legal limit. So we can take: dlog(pd) dlog(l) = This means a reduction of the legal limit from 80 to 50 would give a 21% reduction in the proportion of drink drivers. Since this would not affect the mean BAC all casualty classes would be affected similarly, and we might hope that motorcyclists, and hence motorcycle casualties, will behave in the same way. An important assumption in this calculation is that the level of enforcement is maintained. This is not simply a matter of performing the same numbers of screening breath tests each year, for the number of positives and hence the number of drink drive prosecutions can be expected to rise sharply. With the mean BAC of 37, some 11% of drink drivers are over the limit and 14% lie between BAC 50 to 80. This means that there would be a net increase in the number of positives from 90 thousand a year at present (1995 level) to 160 thousand. This is almost 50% greater than the peak level of positive breath tests in 1987/8, and significant additional police resources may be required to handle the extra cases. This would be essential if the pressure on drink drivers at the more critical, higher end &the BAC distribution is to be maintained. In the case of a zero limit, we cannot simply assume that the elasticity is constant, for that is the same as the assumption that the proportion of drink drivers would fall to zero. Eliminating drink driving will not be as easy as that. Equation 6 provides the following relation between the elasticities which can be used to calculate the change in a number of steps. dlogod) -xl dlog(d) dlog(l) l+xl dlog(e)...9 Table 5 shows the effect of further reducing the legal limit, using the same assumptions as above in the calculation of the effect of a 50 limit. Again, the critical assumption in the zero limit is that the mean BAC among drink drivers will remain unaltered. In fact this may be even more realistic, for the only change in drinking habits that complies with this law is either to refrain from drinking or to walt till all the alcohol was metabolised. There is scope then for reducing the level of drink driving to one third its present level and the value of the casualty cost savings would more than justify the effort involved. On the other hand, this would be a clearly be a serious undertaking, with large increases in police resources required to maintain 340

11 enforcement levels and there would be a clear case for the introduction of a fixed penalty system for low level offenders. Table 5. Effects &Lower Legal Limit in the UK CONCLUSIONS Limit Reduction in Positive Breath Tests Casualty Cost Drink Driving Annually (thousands) Saving ( M) 50 21% % Zero 65% We may conclude then that while the UK drink drive record is good, there is still considerable scope for improvement. A reduction of the legal limit to 50 should provide a 21% reduction in both drink driving and casualties in its associated accidents without an undue increase in police resources for enforcement. With lower limits, the implications for police resources would have to be carefully considered. REFERENCES Allsop, R.E. (1966) Alcohol and Road Accidents. RRL Report 6, TRL. Sabey, B.E.;Everest, J.T.; Forsyth, E. (1988) Roadside Surveys of Drinking and Driving. TRRL Research Report 175, TRL. Broughton, J.: Stark, D.C. (1986) The Effect of the 1983 Changes to the Law Relating to Drink Driving. TRRL Research Report 89, TRL. Stark, D.C. (1986) BAC in Motorists in the UK. TRRL Working Paper RS/31, TRL. Stark, D.C. (1987) Risk of Fatal Accidents to Drinking Drivers and Pedestrians. Second International Conference on Road Safety, Groningen. Stark, D.C. (1986) Prediction of Driver Risk from the Accident History. Paper RS/86, TRL. TRRL Working Rabbitt, P.M.A. (1993) Alcohol, Reaction Time and Memory. British Journal of Psychology No. 89. Jurkovich, J.G. et al. (1993) The Effect of Acute Alcohol Intoxication and Chronic Alcohol Abuse on Outcome from Trauma. Journal of the American MedicalAssociation. No Evans, L.: Frick, M. (1993) Alcohol's Effects on Fatality Risk from a Physical Insult. No. 54. Caiman, K. (1996) Annual Report of Chief Medical Officer for England. 341

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