EVALUATION OF A DRUNK DRIVING WARNING SYSTEM. * A. Bodi, Ph.D.; R. E. O'Connor, Ph.D.; and M. J. King, B.Sc. (Hons), M.A.P.S.

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1 EVALUATION OF A DRUNK DRIVING WARNING SYSTEM * A. Bodi, Ph.D.; R. E. O'Connor, Ph.D.; and M. J. King, B.Sc. (Hons), M.A.P.S. SYNOPSIS The Drunk Driving Warning System is an alcohol interlock based on performance of the Critical Tracking Task (CTT). An evaluation was undertaken to determine CTT sensitivity to blood alcohol concentration (BAC), particularly at.05 g/100 ml. Subjects were 36 males in 3 age groups (18, 21 to 25, 35 years and above) divided into 2 alcohol consumption categories ("light" and "heavy"), and scored on 4 training and 2 test days (one alcohol and one placebo). The CTT performance declined as BAC increased and was significantly impaired at.05 BAC. However, performance was too variable for in-vehicle use. Age and alcohol consumption pattern were without effect. INTRODUCTION Since the early 1970's, the U.S. government (specifically, the National Highway Traffic Safety Administration, the NHTSA) has been involved in the development and evaluation of vehicle-borne devices to prevent or discourage drivers from starting their vehicles while intoxicated. A testing program has investigated a number of different kinds of devices including "chemical" breath-testing systems and "performance" systems based on impairment found under alcohol of the usual sober performance level on some behavioral measure. One of the most promising of these systems is the Drunk Driving Warning System (DDWS). The DDWS, which has been tested extensively by Systems Technology in California, is intended for use by convicted drink drivers as a warning system rather than as a preventive device (given the possibility of emergency situations where the vehicle must be driveable). The DDWS requires the driver to perform a task designed to estimate alcohol impairment before driving the vehicle. The Critical Tracking Task (CTT), a visual-motor compensatory tracking task, forms the basis of the most thoroughly investigated version of the DDWS. k Road Traffic Authority, 801 Glenferrie Road, Hawthorn, Victoria 3122, AUSTRALIA. 179

2 The CTT, developed originally for pilot and astronaut training, uses a small dashboard-mounted meter in which a hinged needle moves to the left or right from the vertical. The driver is required to keep the needle centered using appropriate movements of the steering wheel. This task becomes more difficult as the angular velocity of the needle deflections increases. Failure to reach a pre-selected level of CTT performance results in the activation of the alarm portion of the DDWS involving the operation of emergency flashers, and if the car exceeds a speed of 10 mph (16 km ph) the sounding of the car horn at 1-second intervals. After a failure, the driver is required to wait 10 minutes before the task in attempted again. Various procedures ensure that the driver, rather than a sober accomplice, completes the test. In 1979, the Road Safety and Traffic Authority (which became part of the Road Traffic Authority on July 1, 1983) entered into a joint research project with NHTSA to evaluate the CTT-based DDWS in Victoria. Victorian law specified.05 g/100 ml as the blood alcohol concentration (BAC) beyond which driving a motor vehicle is illegal. This contrasts with the higher levels (typically.10 g/100 ml) in the U.S. One major focus of the evaluation was, therefore, to determine the viability of the CTT in this lower BAC case. Substantial evidence indicates that CTT performance is significantly impaired at high BAC's ( g/100 ml) relative to sober performance (e.g. Klein & Jex, 1975; Tennant & Thompson, 1973). Allen, Stein, Summers, and Cook (in press) have suggested that a "pass level" for each trial should be set close to the average performance level, specifically, at the 40th percentile of well-practiced sober performance so that the probability of failing a trial (i.e. of falling at or below this level) is 40%. Furthermore, Allen et al. have suggested that the driver should be given a maximum of 4 attempts to pass a trial. If all 4 trials are failed, the "test" is failed and the alarm systems are activated. If, and as soon as, one trial is passed the car may be driven normally. This method gives a low sober failure rate of.4x.4x.4x.4 =.025 or 2.5% for the test and produces test failure rates around 75% at a BAC of.15 g/100 ml. Far less evidence is available concerning CTT sensitivity at.05 g/100 ml BAC. Dott and McKelvey (1977) claimed to find significant impairment for a target BAC of.05 g/100 ml (mean achieved BAC of.048 g/100 ml). However, other studies which have included lower BAC levels (e.g. Klein & Jex, 1975; Tennant & Thompson, 1973) have generally examined larger intervals (e.g., g/100 ml) rather than specific points, like.05 g/100 ml. 180

3 The major aim of the present study was to investigate further CTT sensitivity to alcohol, particularly at.05 g/looml BAC, in order to assess the viability of the CTT-based DDWS in the Victorian context. In addition, the study was intended to investigate the possibility that the CTT may be differentially sensitive for the different age groups and categories of drinking history found among convicted drink drinkers, given some indications in the literature that older subjects and "lighter" drinkers may be more impaired than younger subjects and "heavier" drinkers, respectively, at corresponding BAC's (e.g., see Klein & Jex, 1975; Linnoila et al., 1980; Thompson et al., 1975). Materials METHOD A CTT device was installed on the dashboard of a laboratory buck which simulated the interior of a Ford Falcon XD. An Intoxilyzer breath alcohol analyzer was used to estimate BAC. Design The between-subjects variables in the experiment were Age (3 levels: 18 years, years, and 35 years and over) and Drinking History (2 levels: a "lighter" and a "heavier" level). Thus, there were 6 different groups of subjects, with 6 subjects in each group. The within-subjects variables in the experiment were Alcohol Condition (2 levels: Alcohol and Placebo, referring to scores derived on an alcohol test day and a corresponding placebo day) and Cycle (5 levels: referring to scores derived at target BAC levels 0,.025,.05,.075, and.10 g/100 ml on the alcohol day and at corresponding points on the placebo day). Subjects Thirty-six medically-fit male volunteers took part, drawn mainly from students, the unemployed, and employees of the Road Traffic Authority. (Practical difficulties precluded the use of convicted drink drivers.) Nondrinkers and very heavy drinkers were excluded. "Lighter" drinkers consumed g/week and "heavier" drivers g/week. (See Bodi et al., 1983, for further details.) The age range in the oldest category was years. 181

4 Procedure Each subject undertook 4 training sessions and 2 test sessions spread over 2 weeks. Training procedures to achieve stable sober performance levels were similar to those recommended by the U.S. studies. Half of the subjects were alcohol-tested on the first test day and placebo-tested on the second; and the other half, vice-versa. Each subject performed 5 cycles on each day. Each of these involved 2 breath tests, drink administration, a waiting period, 2 breath tests, and a block of 8 CTT trials. For the first cycle, all subjects received a placebo drink in 20 minutes and waited 10 minutes. On the alcohol day, the second cycle involved a drink calculated to produce.025 g/100 ml BAC and a 40-minute wait, whereas the remaining 3 cycles had a 10-minute drink period and a 40-minute wait with target BAC's of.05,.075, and.10 g/100 ml, respectively. The alcohol doses were presented as a 20% v/v solution of ethanol and low-calorie orange juice; doses for each subject were calculated on the basis of Total Body Water estimates (Watson et al., 1980; 1981). The placebo subjects underwent the same procedure except that they received placebo drinks consisting of orange cordial with 2 ml of ethanol "floated" on top. (See Bodi et al. 1983, for more details.) RESULTS The impairment at a target BAC of.05 g/100 ml (with achieved BAC,.053) was 4.6% of the corresponding placebo score and at.10 g/100 ml (with achieved BAC,.100), 15.4%. Allen et al. (in press), in their review of previous CTT findings, reported that impairment at.10 g/100 ml BAC is usually around 10%; if anything, the present experiment shows more impairment than is generally obtained. (See Figure 1 and Table 1.) TABLE 1 Mean CTT scores for all 36 subjects for the 5 Cycles on Alcohol and Placebo test days. CYCLE (Target BAC for Alcohol day in brackets) (1) (.025) (.05) (.075) (.10) Placebo Alcohol T 7 l l

5 The data were analyzed in a 3 (Age) x 2 (Drinking History) x 2 (Alcohol Condition) x 5 (Cycle) analysis of variance (see Table 2). The main effect of Alcohol Condition was highly significant (F = , df = 1/30, greater than.0001) as was the main effect of Cycle (F = 35.51, df = 4/120, greater than.001) and their interaction, (F = 38.26, df = 4/120, greater than.0001), reflecting the fact that the placebo data remained relatively constant but the alcohol scores decreased with increasing BAC. (The effects of Age and Drinking History were all nonsignificant; F's less than 1.00). TABLE 2 ANALYSIS OF VARIANCE SUMMARY TABLE FOR ANALYSIS OF EFFECTS OF AGE, DRINKING HISTORY, AND BAC ON CTT PERFORMANCE Source df MSq F_ Age (A) Drinking History (DH) A x DH Error Alcohol Condition (AC) AC x A AC x DH AC x A x DH Error Cycle (C) C x A C x DH C x A x DH Error AC x C AC x C x A AC x C x DH AC x C x A x DH Error

6 Furthermore, a planned comparison at.05 g/100 ml BAC was made of the data for.05 g/100 ml Target BAC and corresponding Placebo scores in a 3 (Age) x 2 (Drinking History) x 2 (Alcohol Condition) analysis of variance (see Table 3). A significant main effect of Alcohol Condition was found (F = , df = 1/30, greater than.0001) indicating impairment at.05 g/100 ml. No other effects were significant. TABLE 3 OF AGE, ANALYSIS OF VARIANCE SUMMARY TABLE FOR ANALYSIS OF EFFECTS DRINKING HISTORY, AND ALCOHOL IMPAIRMENT AT.05 q/100 ml TARGET BAC Source df MSq F Age (A) Drinking History (DH) DH x A Error Alcohol Conditior (AC) A x AC DH x AC A x DH x AC Error Finally, to assess whether this significant impairment at.05 g/100 ml BAC can be translated into a viable method for using CTT scores to fail substantial proportions of drivers at this BAC without inconveniencing sober drivers, we carried out a post-hoc analysis in which pass levels were set based on sober performance data from the Placebo Day and Cycle 1 of the Alcohol Day. The scores on each cycle of the Placebo Day on the.025,.05,.075, and.10 g/100 ml BAC cycles of the Alcohol Day were then coded as follows: each of the cycles comprised 8 scores; these were divided into 2 "test" blocks of 4, and each test was coded as a "fail" (if all 4 trials were failed) or a "pass" (if at least 1 trial was passed), allowing the calculation of test failure rates at different BAC levels. We found that the sober failure rate was 6%, higher than the aim of around 2.5%. Even so, only 21% of tests were failed at.05 g/100 ml BAC, although 54% were failed at.075 g/100 ml and 75% were failed at.10 g/100 ml BAC which compares favorably with the Figure 5 in Allen et al. (in press). The failure rate at.05 g/100 ml is clearly inadequate with only 1 out of 5 of tests failed. A number of minor adjustments in pass criteria reduced sober failures slightly in some cases, but failure rates at.05 remained around 20-25%. 184

7 Unless sober failure rates are set at higher and probably less acceptable levels (e.g., 10-15%), it seems impossible to increase failure rates at.05 g/100 ml BAC above 30-40%, although failure rates at higher BAC's of g/100 ml can frequently reach 70-80%. In fact, the data in the report by Allen et al. show that failure rates only begin to increase substantially around.07 g/100 ml BAC. The failure rate at.075 g/100 ml in the present case was 54%. DISCUSSION The major result of interest is that although CTT performance is significantly impaired at.05 g/100 ml BAC relative to 0 BAC, it does not appear possible to translate this into a satisfactory method for using CTT scores in order to fail substantial numbers of drivers at.05 BAC while maintaining very low sober failure rates. Therefore, it does not appear realistic to install the CTT-based DDWS into the cars of Victorian convicted drinking drivers to discourage driving at levels just above.05 g/100 ml, although the device may still be effective in reducing accidents. Of drivers killed in Victoria in the years who had BAC's exceeding.05 g/100 ml, 68% exceeded.15 g/100 ml. It may be reasonable to aim to discourage drivers from driving at such levels, and the CTT is highly efficient in this range. On the other hand, a situation where such drivers are not reliably warned that they are exceeding the legal limit may be regarded as unacceptable. It can be argued that in the Victorian context, an in-vehicle breath-testing device would be more appropriate than the CTT (see Johnston, 1981). Two major factors appear to differentiate the Victorian situation from that in the U.S. where breath-testing devices have received relatively little attention. First, the lower legal BAC renders the CTT (and possibly other performance-based devices) less useful in Victoria than in the American case. Second, objection to the use of direct breath-testing measures appears to be less in Victoria where per se laws have been in effect since In contrast, in the U.S. greater emphasis seems to have been placed on the impairment produced rather than the BAC per se: since individuals vary in impairment shown at particular BAC's, impairment itself should be measured (see Johnston, 1981; Thompson et al., 1975). 185

8 CONCLUSIONS CTT performance was found to decrease with increasing BAC. This effect was significant at.05 g/100 ml BAC, the legal limit in Victoria, without modification by Age or Drinking History. The selection of a suitable criterion pass level for practical CTT use was examined no criterion level offered an acceptable balance between failures by drivers above.05 g/100 ml and failures by sober drivers. ACKNOWLEDGEMENTS Dr. Peter Vulcan, Chief General Manager of the Road Traffic Authority, initiated this joint project with NHTSA. His support is gratefully acknowledged, as is the assistance of Prof. Frank McDermott and Prof. Sir Edward Hughes, Department of Surgery, Monash University, for provision of laboratory services and medical supervision. Dr. Glen Smith, Department of Psychology Melbourne University is thanked for the statistical analyses. The DDWS equipment and technical consultation were provided by NHTSA, and the laboratory buck was generally donated by Ford Australia. REFERENCES Allen, R. W., Stein, A. C., Summers, L. G., and Cook, M. L. (in press). Drunk Driving Warning System (DDWS). Volume I - System Concept and Description. Report to the U.S. Department of Transportation, DOT Contract No. DOT-HS Washington, D.C.: Department of Transportation. Bodi, A., O'Connor, R. E., King, M. J., McDermott, F. T., and Hughes, E.S.R. (1983). Laboratory and Field Testing of a Drunk Driving Warning System. RTA Report to the U.S. Department of Transportation. Washington, D.C.: Department of Transportation. Dott, A. B., and McKelvey, R. K. (1977). Influence of ethyl alcohol in moderate levels on visual stimulus tracking. Human Factors, 19; Johnston, I. R. (1981). Drunk Driving Warning System - An Evaluation Policy and Plan. Internal Report AIR Camberra: Australian Road Research Board. 186

9 Klein, R. H., and Jex, H. R. (1975). Effects of alcohol on a critical tracking task. Journal of Studies on Alcohol, 36: Linnoila, M., Erwin, C. W., Ramm, D., and Cleveland, W. P. (1980). Effects of age and alcohol on psychomotor performance of men. Journal of Studies on Alcohol, 41; South, D. R., and Key, D. (1983). Specific Deterrence and Rehabilitation of Convicted Drinking Drivers - The Accident Potential as Yet Unrealized. RTA Report. Hawthorn, Victoria: Road Traffic Authority. Tennant, J. A., and Thompson, I. (1973). A critical tracking task as an alcohol interlock system. Paper presented at the International Automotive Engineering Congress and Exposition, Detroit, Michigan, January Thompson, R. R., Repa, B. S., and Tennant, J. A. (1975). Vehicle-borne drink driver countermeasures. In Israelstam, S., and Lambert, S. (eds.), Alcohol, Drugs, and Traffic Safety: Proceedings of the Sixth International Conference on Alcohol, Drugs, and Traffic Safety. Toronto: Addiction Research Foundation of Ontario. Pp Watson, P. E.,Watson, I. D., and Batt, R. D. (1980). Total body water volumes for adult males and females estimated from simple anthropometric measurements. American Journal of Clinical Nutrition, 33: Watson, P. E.,Watson, I. D., and Batt, R. D. (1981). Prediction of blood alcohol concentrations in human subjects: Updating the Widmark Equation. Journal of Studies on Alcohol, 42:

10 CTT SCORE (0) (.025) (.05) (.075) (.10) CYCLE (Target BAC) Figure 1. Mean CTT scores for each cycle on placebo and alcohol days. 188