alcohol impairment, officer, Sobriety Checkpoints, San Diego, Chattanooga, Charlottesville, VA., breath samples, initial assessment, the officer, Adrian K. Lund, R. Roszbach, Ian S. Jones Insurance Institute for Highway Safety, traffic safety, perceptions, alcohol intoxication, alcohol sensor, Insurance Institute for Highway Safety, Journal of Applied Social Psychology, impaired drivers, alcohol detection, Police officers need
© 1987 Elsevier Science Publishers B.V. (Biomedical Division) Alcohol, drugs and Traffic Safety
- T86 P.C. Noordzij and R. Roszbach, editors.
B 25920 379
DETECTION OF IMPAIRED DRIVERS WITH A PASSIVE ALCOHOL SENSOR
Adrian K. Lund Ian S. Jones Insurance Institute for Highway Safety, Tenth InterNational Conference
on Alcohol, Drugs, and Traffic Safety, September 10, 1986 The Initial Assessment
of alcohol impairment has been one of the weakest link
s in the chain of events leading to the arrest and conviction of alcohol-impaired drivers. In the U.S., once a driver has been stopped, police officers
must first have a reasonable suspicion
of alcohol involvement before proceeding with more detailed testing necessary to make an arrest. Often, this initial suspicion must be developed quickly, and officers have had only subjective methods of alcohol detection such as the sensitivity of their own noses and intuition about suspicious driver behavior to guide them. As a result, many impaired drivers go undetected even after they come into contact with the police. Police officers need a means of quickly and objectively identifying the small percentage of impaired drivers without unduly inconveniencing the vast majority of sober drivers. The passive alcohol sensor (PAS) is a device intended to help meet this need. Developed under the sponsorship of the Insurance Institute for Highway Safety in collaboration with Lion Laboratories Ltd., United Kingdom
, and Prototypes, Inc., United State
s, the PAS incorporates an electrochemical Fuel Cell
alcohol sensor in a standard flashlight. A pump in the PAS draws air through an intake port at the front of the flashlight and across the fuel c e l l ; any alcohol in the air creates a current in the cell proportional to the alcohol content
, and an estimated blood alcohol concentration
(BAC) is displayed. To operate the PAS, an officer approaches the driver in a normal fashion, with the PAS in hand, and engages the driver in conversation. While the driver is talking, the officer positions the PAS about six inches in front of the driver's face and activates the pump. The pump runs for about 5 seconds and the fuel cell begins to react immediately, with the display reaching full value in 10-20 seconds. If the PAS reading indicates alcohol to be present in large amounts or if there are other cues that the driver is impaired, the officer then administers further behavioral tests to determine if an arrest is warranted.
380 The first assessment of the effectiveness of the PAS was performed in sobriety checkpoints in Charlottesville, VA. At these checkpoints, all drivers were stopped briefly by the police, their licenses were checked, and they were asked one or two questions. If the officer suspected impairment, the driver was directed to pull off the road and step out of the car for further testing. When appropriate, this testing included a preliminary breath test on a conventional, hand-held device. If the driver tested positive, the driver was arrested and an evidentiary BAC test was obtained. If the officer did not suspect impairment in the initial 1 0 - 2 0 seconds or if the subsequent tests were negative, the driver continued on his or her way. To perform the study, the sobriety checkpoint procedures were modified slightly to obtain BAC's for all drivers. For some drivers, these were available from the police preliminary breath test or the evidential test. However, drivers released by the police without a test were asked by a researcher for a voluntary breath sample, using a small handheld device for measuring BAC from active breath samples. If the driver's BAC was 0.05 or higher, he or she was driven home by Research Staff
or by an unimpaired passenger. Otherwise, the driver was thanked and allowed to continue on the road. BAC's were obtained for 95 percent of the drivers in the study. The study took place over six weekends ( 1 2 nights); during three weekends officers used the PAS and during three they followed their usual initial assessment procedure. Figure 1 shows that the PAS was effective at sobriety checkpoints where accurate initial assessment is particularly important. Without the PAS, only 24 percent of drivers with BAC's between 0.05 and 0.10 were detained for further testing, compared to 45 percent of such drivers when the PAS was used. For drivers with BAC's of 0.10 or higher, the PAS increased the number detained for further testing from 45 to 68 percent. The PAS also reduced the likelihood of unnecessary delay
to drivers with low BAC's by half. Another strategy being used in the U.S. is specially trained police patrols that focus on detecting people driving under the influence (DUI) of alcohol. The procedures for such patrols differ considerably from those of checkpoints. Not all drivers are stopped; instead, DUI patrols cruise their assigned areas until a driver with suspicious behavior (weaving, driving slowly or erratically, driving without lights) is spotted. The driver is stopped, and the officer engages in often extended conversation with the driver. The driver may or may not remain in the car, potentially reducing the opportunity to get a good reading with the PAS during the initial assessment.
Fig. 1. Percent of Drivers with High BACs Delayed for Testing at Sobriety Checkpoints - Charlottesville, VA.
0.05 < BAC <0.10 BAC >0.10 San Diego
0.05 < BAC <0.10 BAC >0.10 Chattanooga
Fig. 2. Drivers with High BACs Arrested by Special DUI Patrols.
If the assessment suggests alcohol impairment, or if the officer is still suspicious because of the initially observed driving behavior, further behavioral tests are administered. Before this study, there was little or no scientific data
on the effectiveness of these patrols. Most studies have indicated that the assessment of alcohol impairment from behavioral signs is a difficult task . However, the officers in special DUI patrols usually receive additional training in the interpretation of behavioral test results and may be trained in the Gaze Nystagmus test , as well. These factors may produce more accurate estimates of alcohol use than in the checkpoint situations, but it still seemed that the introduction of an objective measure of alcohol might have an impact. The DUI patrol evaluations of the PAS took place in Chattanooga, TN and San Diego, CA
. In Chattanooga, five officers were involved in the evaluation, in San Diego, 10. On each night, officers were randomly assigned to use or not use the PAS, and a researcher rode with each officer. If a driver stopped by the officer was subsequently released, the officer introduced the driver to the researcher, who requested a voluntary breath sample, as in the checkpoint study. If a driver was arrested, BAC's were obtained from the records of the evidentiary tests. In Chattanooga, BAC's were obtained for 93 percent of the drivers; in San Diego, they were obtained for 96 percent. The results of the studies were promising: Officers were more effective detecting drivers with BAC's above 0.10 when they had the PAS than when they did not. But the difference was not statistically significant
and not as impressive as in the Charlottesville checkpoint study (Figure 2). Moreover,
382 the PAS had no effect on the detection of drivers with BAC's between 0.05 and 0.10. The most striking finding was the very high effectiveness of the Chattanooga officers, who arrested 94 percent of the drivers with BAC's over 0.10.with the PAS and 88 percent without it compared to 63 and 56 percent for San Diego officers with and without the PAS and to 68 and 45 percent for the Charlottesville officers, respectively. To some extent, the high arrest rate for the Chattanooga police reflects the larger proportion of very high BAC's among Chattanooga drivers; however, the arrest rate was also high among drivers with BAC's between 0.10 and 0.15. The false positive rate was very low in both the special patrols. In San Diego, only 4 percent of the drivers with BAC's under 0.05 were arrested without the PAS, and only 3 percent with the PAS. In Chattanooga, only one percent of drivers with low BAC's were arrested. The Charlottesville sobriety checkpoint study showed that the PAS was clearly effective in that enforcement situation. The PAS was less effective in the special DUI patrols; however, there was some improvement in the detection of drivers with high BAC's with the PAS. The effectiveness of the PAS when used on standard police patrols has yet to be tested. Most officers have limited training in alcohol detection techniques
, and they may benefit more from the objective information provided by the PAS. Perhaps more importantly, the widespread use of the PAS in regular patrols could serve notice to the public regarding the degree to which the drunk driving laws are being enforced. This could greatly increase the public perception
of the risk of being caught and could have a disproportionately large effect on the deterrence of drunk driving.
Jones, I.S., and Lund, A.K., 1986. Detection of alcohol-impaired
drivers using a passive alcohol sensor. Journal of Police Science and
Administrat ion, 14(2).
Pagano, M.R., and Taylor, S.P., 1980. Police perceptions of alcohol
intoxication. Journal of Applied social psychology
, 10(2), 166-174.
Tharp, V.K., 1981. Gaze nystagmus as a roadside sobriety test.
Abstracts and Reviews in Alcohol and Driving, Ј(2), 5-8.
AF Lund, IS Jones