U.S. Department of Transportation printed on recycled paper

National Highway Traffic Safety Administration

How passive sensors were used 

by officer duty assignment

TRAFFIC TECH

Technology Transfer Series

Number 121 May 1996

PASSIVE ALCOHOL SENSORS TESTED IN 3 STATES

FOR YOUTH ALCOHOL ENFORCEMENT

Enforcing zero tolerance or low BAC laws for under manufacturers were marketing passive sensors for use

21 age drivers presents new challenges for law by police agencies. Each police agency worked with

enforcement officers. It is more difficult to detect the each type of unit for about two months. Sensors were

smaller amounts of alcohol that constitute a zero used on routine patrols, checkpoints, motorcycle and

tolerance violation. A young driver just above a limit bicycle patrols, gang intervention, a Safe

of, say .02%, may not exhibit traditional cues like Neighborhoods Unit (similar to gang or drug

slurred speech and the officer may miss a faint smell of intervention units), and a special youth DWI and drug

alcohol. In addition, the officers’ training, focus, and enforcement unit. 

experience have traditionally targeted drivers who are

over the adult limit of .08 or .10%, or drivers who

show obvious signs of impairment.

A promising technology for enhancing impaired enforcement context during the 6 month field trial. 

driving enforcement, especially at lower BAC levels, is Most uses (83 percent) were for drivers contacted as

the passive alcohol sensor. The sensors are designed part of routine patrol or traffic operations.

to sample the air immediately around the suspect for

signs of exhaled alcohol -- the same air that is

available to the officer’s nose. Rather than giving a

precise BAC level, sensors typically indicate the

presence of alcohol, but not the amount.

Passive alcohol sensors have been evaluated in

laboratory settings, at sobriety checkpoints, and in

some limited police applications. The National

Highway Traffic Safety Administration (NHTSA)

sponsored a field evaluation of several different

passive alcohol sensor devices to assess their use as

part of normal or typical police operations. This study

involved the basic acceptance of the devices on their

own merits, as well as, once used, how effective they About 27 percent of all deployments resulted in a

were. The study focused on youth alcohol positive BAC reading and about 16 percent of all

enforcement. tested suspects were charged with an alcohol related

Three municipal police agencies located in states with the sensor, about 60 percent were charged. An

zero tolerance laws participated in the study. alcohol charge was more likely for persons under the

Chandler, Arizona; Hamilton Township, New Jersey; age of 21. The next figure shows arrests made by the

and Murfreesboro, Tennessee are all mid-sized type of enforcement activity, including non-traffic

agencies with a sworn officer strength of about 100 or related alcohol arrests. Uses involving more underage

more officers. At the time the study began, three persons, such as the gang patrols and youth DWI,

27 Percent of Sensor Uses Were Positive

The sensors were used about 1,000 times in an

violation. Of those with any positive BAC reading on
Percentage of cases leading 

to alcohol-related arrests

yielded alcohol-related arrests half of the time.

Total DWI Arrests Did Not Change 

The total number of underage liquor law and DWI use over time.

arrests across jurisdictions did not show changes when

compared to preceding time periods. 

Sensor Use Declined Over Time Alcohol Sensors, (58 pages plus appendices) prepared

Use of the sensors declined substantially over time,

regardless of the type of sensor and in every one of the

police agencies. About half of all uses occurred during

the first two month test period; one third during the

second; and one sixth during the third.

Officer Reactions to Passive Alcohol Sensors

Officers and their departments were positive overall

about the sensors, but there were differences between

situations and devices. The report catalogues

comments and suggestions specific to each device. 

Officers were concerned about officer safety when

using the devices for initial screening in normal traffic

stops. Participating officers said passive alcohol

sensors were particularly useful in four situations.

1. Sobriety Checkpoints

2. Crash investigations after securing the location

and obtaining treatment for the injured

3. Underage liquor law and zero tolerance

violations

4. School and community presentations

Sensors were viewed as less useful for routine patrol

operations which largely accounts for their decline in

HOW TO ORDER ! ! ! ! ! ! ! !

Limited copies of the Effectiveness of Passive

by Preusser Research Group of Trumbull, CT are

available. Write to the Office of Program

Development and Evaluation, NHTSA, NTS-33, 400

Seventh Street, S.W., Washington, DC 20590, or

send a fax to (202) 366-7096. Linda Cosgrove,

Ph.D., was the contract manager.

U.S. Department 

of Transportation

National Highway 

Traffic Safety 

Administration

400 Seventh Street, S.W. NTS-33

Washington, DC 20590

TRAFFIC TECH is a publication to disseminate 

information about traffic safety programs, 

including evaluations, innovative programs, 

and new publications. Feel free to copy it as you wish. 

If you would like to receive a copy contact:

Linda Cosgrove, Ph.D., Editor, Evaluation Staff

Traffic Safety Programs

(202) 366-2759, fax (202) 366-7096

E-MAIL: lcosgrove@nhtsa.dot.gov