Ignition Interlock Devices: An Overview and the

Future

Jam es F. Frank

National Highway Traffic Safety Administration, Washington, DC, U SA 1

The Early Years

Almost thirty years ago, when some of us had not yet even thought about careers in traffic

safety, Voas (1969) wrote about «cars that drunks can’t drive». In this early paper, the concept

o f an «Alcohol Safety Ignition-interlock System* (ASIS) was introduced. Ignition interlocks

were viewed not as a substitute for other alcohol general deterrence countermeasures, but as just

another tool for court use. The course was set early and is still on much the same track. In these

early years, developers considered both performance-based interlock devices and alcohol breath

test-based devices. It remained for future research and field experience to shape the decades to

come.

T he Com m ercial B eginnings

Primarily because it proved too difficult to distinguish between alcohol impairment and

performance deficits caused by other factors, performance-based interlock systems were not

seriously pursued after the early 1980s (see Compton, 1988 for a more detail about this early

period). While prototypes o f the earliest breath test based interlocks were created in the late

1970s, the first commercial devices were introduced in the mid-1980s. NHTSA evaluated three

of those devices in its laboratories (Frank, 1988), and found them to consistently identify low

as well as high BAC users who followed instructions. However, devices from this generation

could be fairly easily circumvented by a motivated individual with preplanning and some

knowledge. In the following years, NHTSA (1992) helped establish requirements for device

performance by developing model specifications for ignition interlock devices.

M aturation in the 1990s

By the early 1990s , the first studies evaluating ignition interlock programs appeared. All o f

1 T he view s in this paper are those o f the author alone and do not represent the view s o r policy o f the National

H ighw ay Traffic Safety A dm inistration (N HTSA ) o f the U .S. D epartm ent o f Transportation.

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these studies suffer from the same basic shortcoming, namely that people who participated in

interlock programs were self-selected or court-selected and thereby biased. Of course, it would

have been better to find a jurisdiction where study participants were assigned randomly to either

a program group or a control group, but it has taken another five years before that has occurred

(Beck, et al, 1997). With the understanding that selection biases probably played some role in

the outcome described in these studies, they must still be examined seriously as they represent

the first major efforts to evaluate interlock programs. Consider the major studies from this

period.

Morse and Elliott (1992) reported on a 30-month drinking and driving study in Hamilton

County (Cincinnati), Ohio. They reported that interlock devices installed on DUI offenders

«...substantially reduced the incidence of a repeat DUI arrest compared to a group o f persons

whose license had been suspended, but did not get an interlock*. The failure rate o f the

interlock group (3.4%) represented a 65% decrease in the likelihood o f repeat DUI arrest

compared to the 9.8% failure rate of a license suspension group. Morse and Elliott

acknowledged that it is difficult to generalize their findings because o f selection bias problems,

but nevertheless, the findings were promising enough to warrant continued interest in and study

o f ignition interlock programs.

Popkin, et al. (1992) examined a sample of about 700 multiple DUI offenders on an interlock

program in North Carolina in the early 1990s. While subject to the same selection bias criticism

as the Morse and Elliott work, Popkin, et al. reported that the interlock program reduced

recidivism while devices were installed on vehicles. However, the suppression effect appears to

have been lost when program participants had the devices removed. The study findings suggest

that interlocks suppress drinking and driving when the equipment is on the vehicle, but that the

effect does not carry over to the period after the interlock is removed. In other words, these

findings suggests that without the controls provided by the interlock device, persons with a

history of DUI offenses (and probably, alcohol problems) are more likely to relapse and

recidivate when the interlock is removed than when it is left on the vehicle. More data in support

o f this conclusion are required before it can truly be embraced.

Jones (1992) attempted to evaluate the effectiveness o f an ignition interlock program in Oregon.

While he was able to show that ignition interlock devices reduced recidivism rates as long as the

device was on the vehicle, he was unable to show that this intervention was more effective than

license suspension by itself. Jones painstakingly identified the sampling biases associated with

various groups he studied, thereby clearly identifying what he could not say based on the

limitations o f his research design.

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The suggestive, but incomplete picture painted by the studies o f the early 1990s have not

inhibited a good number o f U.S. state legislatures from passing laws enabling the interlock

concept to be introduced more widely. In 1997, there are thirty-four states that have passed

some sort o f ignition interlock legislation. However, just because states have passed laws does

not mean there are mature, well-oiled interlock programs in operation. States have typically

adopted the NHTSA model specifications as their own, thereby establishing certification criteria

for devices used in their jurisdictions. Once devices have been approved for use in a given state,

the interlock program still needs to be established. Again, typically, these programs involve

convicted DUI offenders having to apply for interlock use as a condition o f license

reinstatement after a period o f hard suspension. Some jurisdictions authorize interlocks as a

condition o f probation authorized by the courts at the time o f sentencing. The answer to the

fundamental question o f what impact these various programs have on DUI recidivism remains

incomplete.

The current generation of studies continues to examine whether the use o f ignition interlocks

has an impact on DUI recidivism. While this work has not been published and researchers

responsible for this work will need to speak for themselves, a few efforts have interesting

features worth noting.

In a joint U .S.-Canadian collaborative effort, Marques and Voas (1995) (as well as Marques,

Voas, and Beim ess (1997), in a study funded by the U. S. National Institute on Alcohol Abuse

and Alcoholism (NIAAA), are examining the effects o f the use o f ignition interlocks in

combination with TREATM ENT to see whether the added dimension o f monthly contacts with

a treatment provider will affect offenders’ recidivism rates.

Etzkom and Martin (1997) expect to report out on an evaluation o f the Illinois ignition interlock

program by the end of the year. While their study suffers from the same selection biases as

previous studies, the Illinois work will be important for several reasons. First, by the time the

study is completed, more than 1,000 interlock users will have participated in the program. This

is a larger number than most other programs for which data have been reported. Secondly,

Etzkom and Martin plan on comparing a group of interlock users to a matched control group of

persons meeting the same criteria for interlock eligibility from a period several years before

implementation o f the interlock program. This comparison, though not perfect, should help

shed further light on the effects o f interlocks. The Illinois program will also look at data on

what happens to former interlock users when the interlock is removed from their cars and they

return to driving without it.

Beck, et al. (1997), in a study sponsored by the Insurance Institute for Highway Safety in the

U .S., have made a number o f public presentations describing this very important Maryland

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evaluation. This work is important because it is the only study known to use random

assignment o f subjects to interlock and control groups. Hopefully, the first substantive results

from this work will be reported at this T-’97, ICADATS meeting in Annecy.

The Future.

There are a number o f key questions that future research should help us better answer.

(1 ) Do interlock program s reduce recidivism o f DU I offen ders w hile the

interlock is insta lled on vehicles?

Evidence to date suggests the answer to this questions is probably yes, though its relative

effectiveness compared to license suspension is very difficult to determine. Critics o f interlock

devices frequently point to those who make a sport out o f defeating or circumventing interlocks,

either by driving other vehicles or finding ways o f driving their own vehicle. While some may

be able to defeat the system, anecdotal reports to date suggest that the vast majority o f users do

not drink and drive when the device is installed on their vehicle.

(2) W hat happens to interlock users when the interlock is rem oved from the

vehicle and they are allowed to drive again without it?

The few studies that have looked at data addressing this question suggest that the interlock

suppresses drinking and driving, but does not prevent its reoccurrence when the interlock is

removed. However, data addressing this question are still incomplete and we need more data

before we can make stronger statements. Nevertheless, these findings are consistent with our

understanding of the likelihood of relapse among persons with alcohol problems. If the data

bear out this trend, the question becomes: what can one do to reduce the likelihood of relapse or

renewed drinking and driving. In this context, studies examining the effects o f a treatment

dimension become critically important.

(3) D oes the additional condition of treatm ent added to interlock use further

reduce DUI recid ivism , and if so, is this effect lasting only as long as the

interlock is on the car, or does it have som e longer term im pact?

The role o f treatment for interlock users is an important one, but one about which we still have

too little data to draw any firm conclusions. The working hypothesis is that treatment in

combination with interlock use will further reduce the likelihood of recidivism. However, data

to support or refute this hypothesis are still pending.

Interlock manufacturers have indicated that they are «in the black», suggesting that the interlock

business is a viable one, though perhaps still struggling. Informal reports from manufacturers

suggest there may be as many as 20,000 devices in use in the U.S. today. As long as judges

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and legislatures perceive this approach as having a chance of reducing recidivism and it can be

implemented at minimal cost to taxpayers, it seems likely that programs will continue to grow.

In concert with this growth and prolonged use o f interlocks, it is hoped that research of the next

5-10 years will allow us to draw more definite conclusions about the effectiveness o f ignition

interlock programs. Another generation o f research reports is needed before the picture is

clearer.

R E FE R E N C E S

Beck, KH, Rauch, W J and Baker, EA (1997) «A Randomized Trial o f the Effects o f Alcohol

Ignition Interlocks: Status o f a Study with Multiple Offenders in Maryland.* Paper presented at

the 76th Transportation Research Board Meeting, Washington, DC, January 16, 1997.

Compton, RP (1988) «Potential for Application of Ignition Interlock Devices to Prohibit

Operation of Motor Vehicles by Intoxicated Individuals. A Report to Congress* W ashington,

DC: National Highway Traffic Safety Administration, Technical Report No. DOT HS 807 281.

Elliott, DS and Morse, BJ (1992) NIAAA Final Report: In-Vehicle BAC Test Devices as a

Deterrent to DUI.» Rockville, MD: National Institute on Alcohol Abuse and Alcoholism.

Etzkom, LD and Martin, J. (1997) «A Preliminary Report on the Effectiveness o f the Illinois

Secretary o f State’s Breath Alcohol Ignition Interlock Device (BAIID) Pilot Program .*

Presented at the 76th Transportation Research Board Meeting, W ashington, DC, January 16,

1997.

Frank, J. (1988) «Further Laboratory Testing o f In-Vehicle Alcohol Test Devices.*

Washington, DC: National Highway Traffic Safety Administration (NHTSA) Technical Report

No. DOT HS 807 333, Novem ber 1988.

Jones, B (1992) The Effectiveness of Oregon’s Ignition Interlock Program.* Salem, Oregon:

State of Oregon M otor Vehicles Division, unpublished manuscript.

Marques, PR and Voas, RB (1995) «Case-Managed Alcohol Interlock Programs: A Bridge

Between the Criminal and Health Systems.* Journal o f Traffic Medicine, 23(2) 77-85.

Marques, PR, Voas, RB and Beimess (1997) «Preliminary Report o f the Alberta, Canada

Ignition Interlock/Case Management Study.* Paper presented at the 76th Transportation

Research Board Meeting, W ashington, DC, January 16, 1997.

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Popkin, CL, Stewart, JR, Martell, C. and Birckmayer, JD (1992) «An Evaluation o f the

Effectiveness o f the Interlock in Preventing Recidivism in a Population o f Multiple DWI

Offenders.* Raleigh, North Carolina: Final Report for the G overnor’s Highway Safety

Program (Project No. AL-92-02-02. Unpublished manuscript.

Morse, BJ and Elliott, DS (1992) Effects o f Ignition Interlock Devices on DWI Recidivism:

Findings from a Longitudinal Study in Hamilton County, Ohio.» Crime and Delinquency,

38(2), 131-157.

National Highway Traffic Safety Administration (NHTSA) (1992) «Model Specifications for

Breath Alcohol Ignition Interlock Devices (BAIlDs). 57 Federal Register 67: 11772-11787,

April 7, 1992.

Voas, RB (1969) «Cars that Drunks C an’t Drive.» W ashington, DC: National Highway Safety

Research Center, Technical Report.

Voas, RB and Marques, P (1992) « Alcohol Ignition Interlock Service Support.* W ashington,

DC: National Highway Traffic Safety Administration, Technical Report No. DOT HS 807 923,

December 1992.

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