T2007 Seattle, Washington Evaluation of the Use and Benefit of Passive Alcohol Sensors During Routine Traffic Stops James C. Fell and Christine Compton Pacific Institute for Research and Evaluation, Calverton, MD, U.S.A. ABSTRACT Background: Past studies have demonstrated that police officers fail to detect a substantial proportion of alcohol-impaired drivers during traffic enforcement and that the use of passive alcohol sensors (PAS) could increase the driving-under-the-influence (DUI) arrest rate. Objective: Does the use of a PAS in routine traffic enforcement by officers without specialized DUI training increase the detection and arrest rate of alcohol-impaired drivers? Methods: The Anne Arundel County, Maryland Police Department, provided 12 officers (randomly selected) in one traffic patrol squad (Squad A) with a PAS. A comparison squad (Squad B) of 12 officers (randomly selected) performed traffic enforcement without the PAS. After each squad made approximately 500 traffic stops, they switched roles. Squad B officers were trained and equipped with the PAS, and Squad A officers conducted their subsequent traffic stops without the PAS. Each squad again made approximately 500 traffic stops during this second round. Data were collected on each traffic stop (N=2119) from each squad in both rounds including the reason for each traffic stop, PAS results (as appropriate), preliminary breath-test (PBT) results (if used), and citations or arrests (if issued). Results: Overall, there were no differences in the DUI arrest rate between the officers with the PAS and the officers without the PAS when combining both rounds. The DUI arrest rate for night stops was 10% when the PAS was used and 10% when the PAS was not used. The PAS did help officers who made no DUI arrests without the PAS (0%) during nighttime stops but made several DUI arrests with the PAS (5%) during nighttime stops combining both rounds (p<.01). The DUI arrest rate for traffic stops due to unsafe lane changes, failure to drive right of center, and negligent driving was 22% compared to 2% for traffic stops due to speeding and 6% for traffic stops for all other reasons (p<.01). Thirty-two of 34 drivers (94%) with positive PBT results were detected by the PAS. Conclusions: There is some evidence that the use of the PAS increased the detection of alcohol-impaired drivers but no evidence that it increased the overall DUI arrest rate of the officers. The PAS did seem to help officers who typically do not make DUI arrests. In summary, the PAS is probably best used at sobriety checkpoints rather than during routine stops. BACKGROUND Drivers in the United States admit to driving within 2 hours of drinking alcohol close to one billion times annually (Royal, 2003). Clearly, deterrence to impaired driving in the United States is constrained, as only 1 driving-under-the-influence (DUI) or driving-while-intoxicated (DWI) arrest is made for every 88 reported episodes of driving over the illegal blood alcohol concentration (BAC) limit (Zador et al., 2000). Deterrence is a function of the perceived probability of apprehension, the severity of the resulting sanction, and the swiftness with which the penalty is administered. There is substantial evidence that the most important of those factors is the probability of apprehension because the public is generally unaware of the sanctions for DUI and tend to believe that sanctions can be avoided or ameliorated (Ross & Voas 1989; Ross,
1992). Thus, raising the perceived probability of apprehension is the most essential element of an effective DUI enforcement program. The passive alcohol sensor (PAS) is a device developed to assist police in identifying drinking drivers. The PAS draws in mixed expired and environmental air from in front of the subject s face and passes it into a fuel cell sensor that can detect very small amounts of alcohol. The sensor, which is built into the standard police flashlight, displays the estimated BAC of a driver using a nine LED light bar indicator running from.02 (1 bar) to.12 BAC and higher (9 bars). Evidence from police use of the PAS with drivers stopped at random roadside surveys indicates that using a threshold of 6 out of the 9 light bars can identify 74% of drivers with BACs of.08 or higher with a 99% accuracy (i.e., specificity) (Voas et al., 2006). Because the PAS measures alcohol in mixed expired air, it is not as accurate as the evidential devices used to determine the BAC of arrested drivers. The results of these evidential testers are used as evidence in court proceedings. Unlike the evidential devices, however, which are considered a search under the Fourth Amendment to the U.S. Constitution and cannot be administered without reason to believe the driver is impaired, the PAS is not considered a search. The PAS is considered by many in the enforcement arena as an extension of the officer s nose ; consequently, the use of a PAS at any point in the investigation is believed to be constitutional (Fields & Hricko, 1986; Manak, 1986). The PAS has been used most successfully by officers at sobriety checkpoints. A number of studies (e.g., Jones & Lund, 1986; Ferguson, Wells, & Lund, 1995; Ferguson, 1995; Wells, Greene, Foss, Ferguson, & Williams, 1997) have demonstrated that officers at checkpoints fail to detect about half of the over-the-limit drivers they interview and that the use of passive sensors at checkpoints increases the detection of these impaired drivers by approximately 50%. Research conducted by the Insurance Institute for Highway Safety (IIHS) indicates that the PAS units have a smaller effect when used by police on special DUI patrol operations (Lund & Jones, 1987) and on routine patrol (Kiger, Lestina, & Lund, 1993) (an increase in detection of about 8 to 10%). METHODS The objective of this study was to take advantage of a natural experiment wherein the Anne Arundel County, Maryland, Police Department provided 12 officers (randomly selected) in one patrol squad (Squad A) with PAS devices to see if they facilitate detection of impaired drivers. The manufacturer of the sensors (PAS Systems International, Jarel Kelsey) provided the PAS training on how to use and properly maintain the devices. A comparison squad (Squad B) of 12 officers (randomly selected) were not given the PAS devices during the first round of traffic stops. Each squad of officers conducted routine traffic stops over several months, and each squad submitted approximately 500 Traffic Stop data forms. At the end of that period (Round 1), the squads were switched: Squad B officers were then trained by PAS Systems International and equipped with the PAS devices, and Squad A officers enforced the traffic laws without the PAS. Officers from both squads went about routine traffic enforcement for several more months, and another 500 Traffic Stop data forms were received from each Squad (Round 2). Round 1 enforcement activities were conducted from June 2004 to July 2005, and Round 2 enforcement activities were conducted from October 2005 to February 2006. By switching the use of the PAS devices from Squad A to Squad B, factors such as officer
motivation, training, and certain individual differences could be controlled to some extent in the analyses. The actual usefulness of the PAS in detecting impaired drivers should be more obvious. Information on each traffic stop made by each participating officer in both squads was captured on a data form and sent to PIRE for processing and analyses. For the squad using the PAS, usage at the stop, the PAS reading, a PBT result, and whether an arrest was made for DUI were recorded. In addition, reason for the traffic stop and demographics of the driver were recorded. Any arrests, citations, warnings, and violations were recorded, along with the results of any evidential tests. The same data were recorded for the squad not using the PAS, except the data concerning the PAS. The data were processed for 2,119 traffic stops and distributions and various tables were generated and examined. Chi-square tests (two-tail) were used to determine if there were any significant differences in the proportions or rates of interest using the Statistical Package for Social Sciences software (SPSS, 1997). The main effect tested was the DUI arrest rates for officers using the PAS compared to officers not using the PAS. RESULTS The DUI arrest rate for night stops when the PAS was used was 10% (54 arrests during 566 stops), and when it was not used, it was also 10% (51 arrests during 490 stops) (see Table 1). Table 1. DUI Arrest Rates by PAS Use (Nighttime only) Arrests for DUI at night stops (both rounds) PAS used 54/566 (10%) PAS not used 51/490 (10%) The basic objective of this study was to determine if the use of the PAS by officers during routine traffic stops detected more impaired drivers and increased the DUI arrest rate. Table 2 shows those results. In Round 1, Squad A (with the PAS) had a significantly higher DUI arrest rate than Squad B (without the PAS): 9% vs. 3% (p<.01). In Round 2, Squad A (now without the PAS) also had a significantly higher DUI arrest rate than Squad B (now with the PAS): 7% versus 3% (p<.01). Overall, when both rounds are combined, there were no differences in the DUI arrest rate between the two squads: with the PAS vs. without the PAS. Table 2. Does the use of the PAS increase the DUI arrest rate? DUI Arrest Squad A (with PAS) Round 1 Round 2 Squad B Squad A Squad B (with PAS) Yes 48 (9%) 17 (3%) 37 (7%) 17 (3%) No 460 (91%) 477 (97%) 501 (93%) 562 (97%) Total 508 494 538 579 Did the PAS help officers who had no DUI arrests when not using the PAS (both rounds combined)? Table 3 indicates the PAS did help these officers somewhat. Without the PAS (both rounds combined), these officers made no DUI arrests in 445 stops (by definition of the
subgroup), but they made 10 DUI arrests (2%) in 402 stops when using the PAS (both rounds combined). However, 48% of their stops with the PAS were at night compared to 32% at night without the PAS, which was significant. So, isolating night stops, these officers made no DUI arrests (0%) in 141 night stops without the PAS compared to 10 DUI arrests (5%) during 194 night stops with the PAS. This difference was statistically significant (p<.01). Table 3. Did the PAS help officers who had no DUI arrests when not using the PAS (both rounds combined)? Without PAS (both rounds) With PAS (both rounds) Stops DUI arrests Stops DUI arrests 445 0 (0%) 402 10 (2%) Yes (p<.01) Night stops DUI arrests Night stops DUI arrests 141 0 (0%) 194 10 (2%) Yes (p<.01) CONCLUSIONS Did the PAS increase the detection of alcohol-impaired drivers at traffic stops in Anne Arundel County, Maryland? There is some evidence that it did. The PAS showed a positive reading overall in 11% of the nighttime stops. In Round 1, the PAS was positive during 20% of the nighttime stops. The PAS detected 94% of drivers with positive PBT results giving an indication of its reliability. The DUI arrest rate in night stops with the PAS was 10%, and during night stops without the PAS, it was also 10%. Therefore, combining both rounds of traffic stops, the PAS did not increase the DUI arrest rates of Anne Arundel County police officers. There is some evidence, however, that the PAS did help officers who typically do not make DUI arrests. Will the officers continue to use the PAS during routine traffic stops? Probably not and certainly not during the day. These results are not surprising. Past research has shown that the PAS is most effective at detecting impaired drivers at checkpoints (increases detection rate by about 50%), but not during routine traffic stops (increases detection rate by about 10%). Past studies have also shown that police officers do not like using the PAS at traffic stops (Leaf et al., 1996). The PAS technology has been in use for more than 20 years, yet the penetration rate into the police community is very low. Substantial improvements in the devices have been made in response to police complaints. Yet only about 4,000 PAS units have been sold to police departments in the past 5 years, and only 8,000 in the past 10 years. Currently, an optimistic estimate of use would be about 2,000 of 500,000 traffic law enforcement officers around the country using the PAS (about a 0.4% penetration rate). The use of the PAS is probably most beneficial at sobriety checkpoints when police typically only have a few seconds to determine whether a driver is impaired by alcohol. Although moderate social drinkers usually exhibit behavioral signs of intoxication at BACs exceeding.08, many alcoholics and problem drinkers show no outward signs such as slurring their words or fumbling with their driver s licenses. Thus, it is important for police to use the PAS at
checkpoint operations. With current Congressional support and funding for highly publicized national sobriety checkpoint blitzes at least two times a year, the use of the PAS at these operations could serve as a general deterrent to impaired driving (Fell et al., 2004) in addition to increasing the detection and arrest of impaired drivers at these checkpoints. The PAS may also be beneficial in the enforcement of zero tolerance laws (no alcohol) for drivers younger than 21. The potential effect of passive sensors on detecting, arresting, and deterring alcohol-impaired drivers has not yet been fully realized. Without further research, education on their potential effectiveness, and improvements in the devices so they can be more easily used in the field, support for their use will not materialize. Police need every tool available to help them enforce the laws. Their time for impaired-driving enforcement is dwindling as competing issues emerge (e.g., homeland security). The PAS has the potential to help police officers, but more acceptance and motivation for their use is needed. Finally, police should be made aware that traffic stops involving unsafe lane changes, driving over the center line, or negligent driving have a very high chance of the driver being alcohol impaired. REFERENCES Fell, J. C., Lacey, J. H., & Voas, R. B. (2004). Sobriety checkpoints: Evidence of effectiveness is strong, but use is limited. Traffic Injury Prevention, 5(3), 220-227. Ferguson, S. A. (1995). Use of passive sensors for alcohol-impaired driving enforcement, Transportation Research Board 74th Annual Meeting, Washington, DC. Arlington, VA: Insurance Institute for Highway Safety. Ferguson, S. A., Wells, J. K., & Lund, A. K. (1995). The role of passive alcohol sensors in detecting alcohol-impaired drivers at sobriety checkpoints. Alcohol, Drugs, and Driving, 11, 23-30. Fields, M., & Henricko, A. R. (1986). Passive alcohol sensors constitutional implications. The Prosecutor, 20(1), 45-50. Jones, I. S., & Lund, A. K. (1986). Detection of impaired drivers with a passive alcohol sensor. Journal of Police Science and Administration, 14, 153-160. Kiger, S., Lestina, D., & Lund, A. (1993). Passive alcohol sensors in law enforcement screening for alcohol-impaired drivers. Alcohol, Drugs and Driving, 9, 7-18. Leaf, W. A., & Preusser, D. F. (1996). Effectiveness of passive sensors (Final Report Contract No. DTNH22-93-C-05022). Washington, DC: National Highway Traffic Safety Administration. Lund, A. F., & Jones, I. S. (1987). Detection of impaired drivers with a passive alcohol sensor. In P. C. Noordzij & R. Roszbach (Eds.), Alcohol, drugs and traffic safety T86 (pp. 379-382). New York: Excerpta Medica. Manak, J. P. (1986). Constitutional aspects of the use of passive alcohol screening devices as law enforcement tools for DWI enforcement. The Prosecutor, 19(3). Ross, H. L. (1992). Are DWI sanctions effective? Alcohol, Drugs and Driving, 8(1), 61-69. Ross, H. L., & Voas, R. B. (1989). The new Philadelphia story: The effects of severe penalties for drunk driving. Washington, DC: AAA Foundation for Traffic Safety.
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