TRAFFIC SAFETY

Alcohol Ignition 

Interlocks Are 

Effective While 

Installed; Less Is 

Known about How to 

Increase Installation 

Rates

Report to the Chairman, Committee on 

Commerce, Science, and 

Transportation, U.S. Senate

June 2014

GAO-14-559

United States Government Accountability Office
United States Government Accountability Office

Highlights of GAO-14-559, a report to the 

Chairman, Committee on Commerce, Science, 

and Transportation, U.S. Senate

June 2014

TRAFFIC SAFETY

Alcohol Ignition Interlocks Are Effective While 

Installed; Less Is Known about How to Increase 

Installation Rates

Why GAO Did This Study

Motor vehicle crashes involving 

alcohol-impaired drivers killed 10,322 

people in 2012 and account for almost 

one third of all traffic fatalities annually. 

Ignition interlocks are one strategy 

states use to combat DWI. In 2012, 

MAP-21 established a grant program 

for states that adopt and implement 

mandatory alcohol ignition-interlock 

laws for all convicted DWI offenders. 

Funding authorization for this program 

expires at the end of fiscal year 2014.

GAO was asked to review the 

effectiveness of ignition interlocks and 

NHTSA’s implementation of the new 

grant program. This report discusses 

(1) what is known about ignition 

interlock effectiveness and (2) the 

extent to which NHTSA has assisted 

states in implementing ignitioninterlock programs, including the grant 

program. GAO reviewed 25 studies 

that analyzed relationships between 

ignition interlocks and DWI arrests and 

fatalities; interviewed NHTSA officials 

and reviewed reports about NHTSA’s 

assistance to states; and interviewed 

representatives from safety-advocacy 

and research organizations, and 

officials involved with ignition-interlock 

programs from 10 states. The states 

were selected based on grant program 

qualification and the number of 

alcohol-impaired fatalities, among 

other factors. The information from 

these states is not generalizable. DOT 

officials reviewed a draft of this report 

and generally agreed with the findings. 

DOT offered technical corrections, 

which we incorporated as appropriate.

What GAO Found

Research GAO reviewed consistently indicated that when installed ignition 

“interlocks”—devices that prevent drivers from starting their cars if they have 

been drinking alcohol—effectively reduce the rate of re-arrest for driving while 

intoxicated (DWI) when installed. But once the devices are removed, DWI rearrest rates return to pre-interlock rates. (Most studies use DWI arrest as a proxy 

for alcohol-impaired driving.) Further, the National Highway Traffic Safety 

Administration (NHTSA) estimated that between 15 and 20 percent of offenders 

arrested for DWI actually install ignition interlocks. Many factors contribute to low 

installation rates. For example, some states lack the resources to monitor 

offenders to ensure they install ignition interlocks; other states require that 

offenders pay fees and penalties to be eligible to install ignition interlocks and 

return to driving with interlocks. State ignition interlock programs vary in terms of 

how they are designed, but little research exists on which specific interlock 

program characteristics—such as monitoring or length of installation—could 

improve the effectiveness of interlock programs. NHTSA is currently conducting 

studies on factors that could help states improve installation rates or otherwise 

improve the effectiveness of their interlock programs. NHTSA expects these 

studies to be completed by 2015. 

NHTSA has offered a variety of technical assistance, research, and education to 

help states establish and improve their ignition-interlock programs, as well as 

implement the ignition interlock grant program established by the Moving Ahead 

for Progress in the 21st Century Act (MAP-21). While state officials confirmed 

that NHTSA’s overall ignition-interlock-related activities have been useful, some 

questioned NHTSA’s implementation of the ignition interlock grant program. 

Specifically, NHTSA’s implementation was based on the plain meaning of the 

authorizing language in MAP-21, which did not include any reference to 

exemptions. As a result, states with “employer exemptions”—programs that 

require offenders to drive only vehicles equipped with ignition interlocks for 

personal use but allow them to drive employer-owned vehicles for work 

purposes—were disqualified. Some state officials told us these exemptions are 

seldom used in practice, but are important to maintain because they facilitate the 

ability of offenders to work. According to NHTSA officials, they recognized that to 

qualify for the grant, many states would have to modify their ignition-interlock 

laws to make them applicable to first time offenders and eliminate exemptions; 

therefore, few states were expected to qualify in the grant’s first years because it 

would be difficult for state legislatures to change their ignition-interlock laws in 

that time frame. In fiscal year 2013, 2 states qualified for the grant; most of the 

additional 12 states that applied for the grant were disqualified at least in part due 

to employer exemptions, but the legislatures in 2 of those states later removed 

such exemptions from their laws, resulting in 4 states qualifying for the grant in 

fiscal year 2014. Because the ignition interlock grant is relatively new, the extent 

to which additional state legislatures may be willing or able to modify their laws to 

qualify for the grant is unclear. A 2012 NHTSA review of states’ impaired-driving 

laws found that at least 5 states’ ignition-interlock laws included employer vehicle 

exemptions, but additional states had other factors that would prevent them from 

qualifying for the ignition-interlock grant.

View GAO-14-559. For more information, 

contact Susan Fleming at (202) 512-2834 or 

flemings@gao.gov
Page i GAO-14-559 Traffic Safety

Letter 1 

Background 2

Research Indicates Interlock Devices Are Effective While 

Installed, but Installation Rates Are Low and Research on 

Strategies to Increase Rates Is Limited 11

NHTSA Provided Assistance to States for Ignition-Interlock 

Programs, but Some State Officials Questioned NHTSA’s 

Implementation of MAP-21 Grant 20

Concluding Observations 24

Agency Comments 25

Appendix I Objectives, Scope, and Methodology 27

Appendix II Studies on Ignition-Interlock Effectiveness 30

Appendix III GAO Contact and Staff Acknowledgments 33

Tables

Table 1: States That Applied For and Were Awarded MAP-21 

Ignition-Interlock Grants, Fiscal Years 2013 and 2014 5

Table 2: Summary of Ignition-Interlock Effectiveness Research 16

Figures

Figure 1: A Driver Using an Ignition-Interlock Device 7

Figure 2: A Generalized Depiction of an Ignition-Interlock Program 8

Contents
Page ii GAO-14-559 Traffic Safety

Abbreviations

AIIPA Association of Ignition Interlock Program Administrators

BAC blood alcohol concentration 

CDC Centers for Disease Control and Prevention 

DOT Department of Transportation

DWI driving while intoxicated 

g/dL grams per deciliter

GHSA Governors Highway Safety Association 

MADD Mothers Against Drunk Driving

MAP-21 Moving Ahead for Progress in the 21st Century Act 

NHTSA National Highway Traffic Safety Administration 

PRG Preusser Research Group 

TIRF Traffic Injury Research Foundation

This is a work of the U.S. government and is not subject to copyright protection in the 

United States. The published product may be reproduced and distributed in its entirety 

without further permission from GAO. However, because this work may contain 

copyrighted images or other material, permission from the copyright holder may be 

necessary if you wish to reproduce this material separately.
Page 1 GAO-14-559 Traffic Safety

441 G St. N.W.

Washington, DC 20548

June 20, 2014

The Honorable John D. Rockefeller IV

Chairman

Committee on Commerce, Science, and Transportation

United States Senate

Dear Mr. Chairman: 

In 2012, motor vehicle crashes involving alcohol-impaired drivers killed 

10,322 people. While the number of such fatalities has dropped by 21 

percent over the last 10 years, almost one third of all traffic fatalities 

annually resulted from crashes involving an alcohol-impaired driver over 

the same period. Breath alcohol “ignition interlocks” are devices that 

prevent a driver from starting a car if the device detects a driver’s blood 

alcohol concentration (BAC) above a certain threshold.1 Ignition interlocks 

represent one of the strategies states use to combat alcohol-impaired 

driving. California first piloted the use of ignition interlocks in 1986 for 

drivers convicted of driving while intoxicated (DWI).2 According to the 

National Highway Traffic Safety Administration (NHTSA), all states have 

enacted legislation requiring or permitting the use of ignition interlocks. 

Historically, Congress has provided funds for state programs to reduce 

alcohol-impaired driving. Most recently, the 2012 surface transportation 

reauthorization act—Moving Ahead for Progress in the 21st Century Act 

(MAP-21)—also included funding for a new grant program for states with 

laws mandating that all drivers convicted of DWI be allowed to drive only 

vehicles equipped with an ignition interlock.3

 

1

BAC is measured as a mass of alcohol per volume of blood. In the United States, the 

standard measurement is represented as grams per deciliter (g/dL).

NHTSA assists states in 

implementing these programs and, in addition to other safety 

organizations, has funded research examining the effectiveness of 

ignition-interlock programs.

2

The specific criminal offenses pertaining to alcohol-impaired driving vary across 

jurisdictions and can include such terms as “driving under the influence of alcohol or drugs 

(DUI),”operating under the influence of alcohol or drugs (OUI),” or “driving while 

intoxicated (DWI)” In this report, the term “driving while intoxicated (DWI)” is used to 

capture all types of alcohol-impaired offenses. 

3

Pub. L. No. 112-141, 126 Stat. 405 (2012).
 

Page 2 GAO-14-559 Traffic Safety

In light of the toll alcohol-impaired driving takes, you asked us to review 

the effectiveness of ignition interlocks and NHTSA’s implementation of 

the MAP-21 ignition-interlock program. This report discusses (1) what is 

known about the effectiveness of ignition interlocks in reducing alcoholimpaired driving and (2) the extent to which NHTSA has assisted states in 

implementing ignition-interlock programs, including the MAP-21 ignitioninterlock grant program.

To identify what is known about the effectiveness of ignition interlocks, we 

reviewed 25 studies conducted between 1990 and 2013 that analyzed 

relationships between ignition interlock devices or programs and alcoholimpaired driving outcomes, including DWI arrests and DWI fatalities. We 

identified these studies from a literature search and recommendations 

from organizations that conduct research on ignition interlocks, such as 

the Pacific Institute for Research and Evaluation. To identify the types of 

assistance that NHTSA provides to states to help them establish and 

implement their ignition-interlock programs, we interviewed NHTSA 

officials about their activities and reviewed reports describing NHTSA’s 

ignition-interlock-related research, technical assistance, and conferences. 

For both objectives, we interviewed representatives from safety advocacy 

organizations such as the Governors Highway Safety Association (GHSA) 

and Mothers Against Drunk Driving (MADD). We also interviewed traffic 

safety, criminal justice, department of motor vehicles or licensing, and law 

enforcement officials from 10 states. The states were selected based on 

MAP-21 ignition-interlock grant program qualification, DWI fatality 

numbers in 2012 (most recent data available), and alcohol-impaired 

fatalities per 100-million vehicle-miles traveled as calculated by NHTSA. 

(See app. I for more information on scope and methodology and app. II 

for a list of reviewed studies.)

We conducted this performance audit from July 2013 to June 2014 in 

accordance with generally accepted government auditing standards, 

Those standards require that we plan and perform the audit to obtain 

sufficient, appropriate evidence to provide a reasonable basis for our 

findings and conclusions based on our audit objectives. We believe that 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives.

While alcohol-impaired driving fatalities have declined from over 21,113 in 

1982 to 10,322 in 2012, the proportion of such fatalities as a percent of 

total traffic-related fatalities has remained relatively constant—between 

30 and 32 percent—over the past 15 years. Congress has targeted this 

Background
 

Page 3 GAO-14-559 Traffic Safety

persistent problem through legislation to encourage states to reduce their 

illegal per se BAC limit.4 For example, beginning in 1982, federal 

legislation authorized grants to states to establish an illegal per se BAC 

limit of 0.10 or greater while driving a motor vehicle.5

NHTSA administers safety-incentive grant programs to assist states in 

their efforts to reduce traffic-related fatalities, including alcohol-impaired 

fatalities.

In other words, with 

respect to a BAC limit of 0.10, anyone whose blood contains 1/10th of 1 

percent of alcohol or higher would be deemed to be DWI. In the late 

1990s, Congress made grant funds available to states to encourage them 

to further lower the illegal per se driving BAC limit to 0.08. In 2000, the 

U.S. Department of Transportation Appropriations Act for fiscal year 2001 

included a provision that states must enact 0.08 BAC laws by fiscal year 

2004 or begin losing federal highway construction funds. According to 

NHTSA, all states had complied with that provision by 2004.

6

Through transportation legislation—including the Transportation Equity 

Act for the 21st Century

NHTSA also provides guidance and technical assistance, sets 

and enforces safety performance standards for motor vehicles and motor 

vehicle equipment, and conducts research on driver behavior and traffic 

safety. As part of such research, NHTSA works with traffic safety 

organizations, such as GHSA, MADD, and the Traffic Injury Research 

Foundation (TIRF).

7

, the Safe, Accountable, Flexible, Efficient 

Transportation Equity Act: A Legacy for Users8

 

4

Per se BAC laws establish the BAC level at which it is illegal per se (in itself) for a driver 

to operate a vehicle, regardless of the driver’s apparent condition or actions. 

, and MAP-21—Congress 

has provided funds to states for programs to combat impaired driving 

(sometimes called “countermeasure programs”). These grant programs 

5

Pub. L. No. 97-364, § 101 (a), 96 Stat. 1738 (1982). Other federal legislation has been 

enacted with the goal of keeping alcohol-impaired drivers off the road, including reduced 

federal funding to states if they did not raise the minimum legal drinking age to 21 and the 

encouragement of “zero-tolerance laws” that set illegal per se BAC levels at 0.02 or 

greater for drivers under age 21.

6

In fiscal year 2014, NHTSA requested a total budget of $828 million and 653 full time 

equivalent employees . NHTSA personnel are located in Washington, D.C. and among 10 

regional offices. 

7

Pub. L. No. 105-178, 112 Stat. 107 (1998). 

8

Pub.L. No. 109-59, 119 Stat. 1144 (2005). 
 

Page 4 GAO-14-559 Traffic Safety

are designed to encourage states to adopt and implement effective 

programs to reduce driving under the influence of alcohol, drugs or the 

combination of alcohol and drugs. Under the most recent countermeasure 

program, states qualify for federal funding based on their impaired driving 

fatality rate and application requirements vary based on whether a state 

has a low-, mid-, or high-range fatality rate.9

• “The Secretary [of Transportation] shall make a separate grant under this subsection 

to each State that adopts and is enforcing a mandatory alcohol-ignition interlock law 

for all individuals convicted of driving under the influence of alcohol or of driving while 

intoxicated.”

In addition, MAP-21 created 

a new grant program with funds available to reward states that implement 

laws requiring ignition interlocks for all individuals convicted of alcoholimpaired driving. Specifically,

10

MAP-21 made up to 15 percent per fiscal year of the total amount of the 

impaired-driving countermeasures grant available for the new ignitioninterlock grant—about $21 million out of $139 million in fiscal year 2013.

Any ignition-interlock grant funds that are not awarded remain available 

for grants under the broader impaired driving countermeasures grant 

program. In fiscal year 2013, 14 states applied for the grant and 2 were 

awarded funding, while in fiscal year 2014, 12 states applied and 4 were 

awarded funding. (See table 1.) States that qualify for this grant can use 

the funds for any authorized traffic safety program, including state 

ignition-interlock programs, other impaired driving countermeasures, or 

even traffic safety activities not related to alcohol-impaired driving. States 

categorized as low-range have the most flexibility in how they may use 

grant funds, while mid-range and high-range states must first obtain 

approval from NHTSA for some activities and meet certain conditions 

before they can be reimbursed. MAP-21 funding will expire at the end of 

fiscal year 2014; Congress is considering reauthorizing funding for 

 

9

NHTSA categorizes states as low-, mid- or high-range based on the average impaired 

driving fatality rate. (Fatality rate is fatalities per 100-million vehicle-miles traveled.) It is 

calculated based on the number of fatalities in motor vehicle crashes in a state that 

involve a driver with a blood alcohol concentration of at least 0.08 percent for every 100 

million VMT. These calculations are based on Fatality Analysis Reporting System data 

from the most recently reported 3 calendar years for a state which are averaged to 

determine the rate. MAP-21 specifies that low-range states are those with an average 

impaired driving fatality rate of 0.30 or lower; mid-range states are those with an average 

impaired driving fatality rate higher than 0.30 and lower than 0.60; and high-range states 

are those that have an average impaired driving fatality rate of 0.60 or higher. 

10See Section 31105(a) of MAP-21, Pub. L. No. 112-141, 126 Stat. 405, 748 (2012).
 

Page 5 GAO-14-559 Traffic Safety

surface transportation programs—including the ignition-interlock grant 

program—for fiscal year 2015 and beyond.

Table 1: States That Applied For and Were Awarded MAP-21 Ignition-Interlock 

Grants, Fiscal Years 2013 and 2014

States that applied for the 

ignition-interlock grant

Fiscal year 2013 

applicants and grant 

awards

Fiscal year 2014 

applicants and grant 

awards

Alaska $0 $0

Arizona $0 $346,639

Arkansas $0 $0

Colorado $0 $0

Connecticut $199,576 $205,258

Illinois $0 $0

Kansas $0 $0

Kentucky $0 a

Louisiana $0

New Mexico

a

$179,271 $184,375

New York $0

Oregon

a

$0 $0

Utah $0

Virginia

a

$0 $0

Washington $0 $416,356

Total $378,847 $1,152,628

Source: NHTSA. | GAO-14-559

a

The first ignition interlock was developed in 1969, but early models relied 

on alcohol sensors that were inconsistent in accurately identifying BAC. In 

the early 1990s, ignition interlock manufacturers began producing more 

reliable and accurate fuel cell sensors, which is a technology currently in 

use.

State did not apply for ignition-interlock grant.

11

 

11According to a 2013 MADD report, there were about 12 ignition interlock manufacturers 

and vendors in the U.S. 

In 1992, NHTSA published model technical specifications for 

ignition interlocks that describe how ignition interlocks should perform and 

how the device can be calibrated to meet the model specifications. 

NHTSA updated these specifications in 2013.
 

Page 6 GAO-14-559 Traffic Safety

Ignition interlocks currently in use have four basic elements:

1. A breath alcohol sensor in the vehicle that records the driver’s BAC 

and sends the signal to not start the engine if the BAC registers higher 

than the predetermined limit (see fig. 1);12

2. A retest system;13

3. A tamper-proof system for mounting the part of the unit that prevents 

the engine from starting, which is typically required to be inspected 

every 30 to 60 days to prevent circumvention; and

4. A data-recording system that logs the BAC results (for the initial test 

and retests) each time the vehicle is turned on and off, the time period 

the vehicle was driven and mileage, and other data that may be used 

by state authorities to monitor the offender’s behavior.

 

12According to NHTSA, states’ requirements for maximum BAC thresholds vary, but 

generally they are set at 0.02 or 0.025.

13The ignition interlock requires the driver to submit breath samples at random times to 

ensure that the driver does not drink alcohol after the engine has been started. The driver 

is given several minutes to exit traffic and move to a safe location to take the test. If the 

breathe sample is not provided or the sample exceeds the set point, the device may warn 

the driver and activate an alarm (e.g., horn blowing, lights flashing) that will continue until 

the ignition is turned off or a breath sample that is within the acceptable limits is provided. 

For safety reasons, the interlock device cannot turn off the vehicle’s ignition once it has 

been started.
 

Page 7 GAO-14-559 Traffic Safety 

Figure 1: A Driver Using an Ignition-Interlock Device 

According to NHTSA, currently all states have enacted legislation 

requiring or permitting the use of ignition interlocks and they generally 

follow the same overall installation and removal process, according to 

Association of Ignition Interlock Program Administrators (AIIPA). (See 

fig. 2.) 
 

Page 8 GAO-14-559 Traffic Safety

Figure 2: A Generalized Depiction of an Ignition-Interlock Program
 

Page 9 GAO-14-559 Traffic Safety

State ignition-interlock programs vary in a number of ways:

• Program design—Some states may incorporate the use of ignition 

interlocks pretrial14, while other states may stipulate ignition interlocks 

only upon conviction (i.e., a state sanctions a “license suspension” 

and then limits the offender to “interlock-restricted driving”).15 Some 

states impose interlock-restricted driving on all convicted DWI 

offenders, while in other states this is only required of those with 

multiple or high BAC convicted offenders.16

 

14For example, Washington’s Department of Licensing administratively suspends an 

offender’s license after arrest but before a DWI conviction. The state provides a period of 

time for the driver to contest such a sanction as a means for providing due process. This 

license suspension is separate from a DWI conviction, per se, as it can occur before trial. 

Further, according to 

NHTSA, most states require a “hard suspension” period in which an 

offender’s driving privileges are denied for a certain period of time 

before he or she may be eligible for interlock-restricted driving. State 

laws and requirements may prescribe ignition interlock requirements 

anywhere from a few months to as long as 10 years or more, often 

with progressively longer ignition interlock requirements for DWI 

offenders who are repeat offenders. Some states also exempt some 

DWI offenders from the application of their state interlock 

requirements. For instance, some states allow employer exemptions, 

which allow offenders to drive employer-owned vehicles without an 

ignition interlock for work purposes. Other states allow exemptions for 

medical reasons, such as allowing offenders who do not have the 

breath capacity to blow a sample into an ignition interlock to not be 

subject to the ignition-interlock installation requirement while at the 

same time suspending their license.

15States may suspend or revoke DWI offenders’ driving privileges pre- or post-conviction 

for a period of time or offer the offender an option for partial license reinstatement upon 

certain conditions such as the offender’s installing an interlock. In some states, an 

offender may elect not to seek a partial license reinstatement, which is commonly referred 

to as “wait out.” For the purposes of this report, we refer to the suspension or revocation of 

a driver’s license or loss of driving privileges as imposed by either the state licensing 

authority or a judicial authority as a “license suspension” and we refer to the partial 

reinstatement of a driver’s license or court-ordered limitations on driving privileges as 

“interlock-restricted driving.” 

16In some states, DWI offenders may not be eligible for interlock-restricted driving 

privileges because of additional factors related to their DWI offense. For example, in 

Illinois, first time DWI offenders who have caused great bodily harm or death were not 

eligible for interlock-restricted driving privileges. 
 

Page 10 GAO-14-559 Traffic Safety

• Program delivery—Requirements for interlock-restricted driving can 

be delivered programmatically in three different ways: through the 

judiciary within the criminal justice system, administratively within the 

driver licensing system, or using a hybrid approach that incorporates 

both judicial and administrative elements. According to AIIPA, 20 

states have judicial programs, 20 states have administrative interlock 

programs, and 10 states have hybrid programs. According to NHTSA, 

in judicially-delivered interlock programs, judges have discretion to 

order interlock-restricted driving and can threaten harsher sanctions 

(e.g., jail time) for non-compliance. In contrast, administrativelydelivered interlock programs are more uniform in imposing 

requirements for interlock-restricted driving on DWI offenders and can 

extend interlock periods or withhold driver’s licenses (i.e., legal driving 

privileges) to encourage compliance, but have fewer sanction options 

at their disposal. There is a growing trend toward more hybrid 

programs.

• Oversight agency—In some states there may be a designated central 

authority that oversees implementation of certain aspects of the 

state’s ignition-interlock program, such as a state department of 

transportation or state law enforcement authority. This agency’s role 

may consist (1) of issuing state performance specifications for ignition 

interlocks; (2) of certifying the manufacturers’ equipment for use by 

testing the equipment directly or by accepting test results as 

conducted by third party laboratories; (3) of approving ignition 

interlock vendors for business in the state; (4) of inspecting service 

centers; (5) of managing data from vendors; and (6) of managing 

state funds to assist indigent offenders with ignition interlock costs, 

among other things.

• Program cost and funding sources—Program costs vary with the 

design of each ignition-interlock program.17

 

17According to NHTSA, states typically require offenders to pay the fees associated with 

an ignition interlock, which in most states range between $65 and $90 per month, plus 

approximately $100 to $250 for each installation.

For example, states 

choosing to monitor ignition interlock data on individual offender BAC 

tests and driving habits will incur greater costs than states that do not. 

Programs that mandate offender appearances before a court or 

administrative body for elevated BAC tests will incur greater costs 

than programs that let the immediate inability to drive serve as the 

offender’s sanction for an elevated test. States have varying 

approaches to funding the delivery of ignition-interlock programs, 

generally using fees paid by DWI offenders. Some states allocate 
 

Page 11 GAO-14-559 Traffic Safety

some portion of collected fees to create indigent funds available to 

help low-income DWI offenders with ignition-interlock costs.

Research we reviewed consistently indicated that ignition interlocks 

reduce the rate of re-arrest for DWI while they are installed on the vehicle, 

but once removed, DWI re-arrest rates return to pre-interlock rates. In 

addition, the percentage of DWI offenders who actually install an interlock 

when ordered is estimated to be low. Several factors contribute to this low 

rate, including low enforcement and monitoring to ensure offender 

compliance and costly fees and penalties that DWI offenders have to pay 

before they are eligible for interlock-restricted driving privileges. Little 

research exists on which specific interlock program characteristics may 

improve installation rates or otherwise improve the effectiveness of 

ignition-interlock programs, but NHTSA’s ongoing and planned 

research—expected to be completed between 2014 and 2015—may fill 

this gap.18

Research consistently indicated that ignition interlocks are effective while 

installed. That is, installation of ignition interlock devices in DWI offenders’ 

vehicles reduces re-arrests for DWI when compared to alternative 

sanctions such as license suspension. Most studies use DWI arrest as a 

proxy for alcohol-impaired driving; however researchers have noted that 

arrest for DWI is a rare event, with some estimating that less than 1 

percent of alcohol-impaired drivers are detected.19

 

18For research studies we included in our review, see appendix II. 

A 2011 review of 

literature assessing the effectiveness of ignition interlocks identified 15 

studies (12 in the U.S., 2 in Canada, and 1 on Sweden) that observed 

that ignition interlock installation reduced the risk of being re-arrested for 

DWI offenders, compared to DWI offenders not using ignition interlocks. 

The studies included in this review primarily evaluated programs directed 

at drivers with multiple DWI offenses or first-time offenders with high BAC 

19NHTSA officials noted that studies they reviewed showed that less that 1 percent of 

drivers who test positive for alcohol (BAC > 0.01) are arrested, and that 2 percent of those 

drivers considered impaired at the time of the study were arrested. 

Research Indicates 

Interlock Devices Are 

Effective While 

Installed, but 

Installation Rates Are 

Low and Research on 

Strategies to Increase 

Rates Is Limited

Ignition-Interlock Devices 

Reduce Re-arrest While 

Installed
 

Page 12 GAO-14-559 Traffic Safety

at arrest (usually >0.15).20 As noted by the authors, the majority of studies 

in this review and those that we separately identified did not randomly 

assign participants to the ignition interlock; therefore, a limitation of many 

of these studies remains the potential for selection bias, as individuals 

who agree to install an interlock may be inherently different from 

individuals who do not agree to do so.21 However, we did identify two 

randomized controlled trials, both in Maryland and limited to offenders 

with two or more alcohol-related traffic violations, that also found that 

ignition interlocks are effective at reducing re-arrests. The first, published 

in 1999, found that being in the interlock program—including installing an 

ignition interlock—reduced a driver’s risk of committing a violation in the 

first year of the program by approximately 64 percent.22 In 2011, 

researchers published a study that replicated the 1999 study with a new 

group of repeat offenders and found that participation in the ignitioninterlock program still reduced drivers’ risk of re-arrest by 36 percent 

while the ignition interlock was installed.23

Research we identified on the effectiveness of ignition interlocks also 

indicates that once the devices are removed, DWI arrest rates return to 

 

20Findings regarding the effectiveness of ignition interlocks for first time offenders are 

unclear, based on study limitations. For example, some studies that aimed to parse out 

effects for first time offenders found no significant effects, possibly due to small numbers 

of first time offenders in the study sample (Tippets & Voas, 1998; EMT Group, 1990; 

DeYoung, Tashima, & Masten, 2005). Other studies not in this literature review only had 

aggravated first time offenders in their sample (such as offenders with a BAC > 0.20) 

which limits the generalizability of these studies to the first time offender population as a 

whole (Roth et al 2007; Morse & Elliott 1992). NHTSA has an ongoing study, which it 

expects to publish in 2014,on the association between state laws requiring all offenders to 

install ignition interlocks and the number of ignition interlocks installed. 

21Additional limitations related to the body of literature we reviewed include the lack of a 

national study on interlock effectiveness and a lengthy time period over which the studies 

were conducted (between 1990 and 2013). Further, without randomization, there may be 

some judicial bias in that judges may choose offenders with certain characteristics for the 

intervention group. Despite these limitations, our review of the literature did provide 

support for the effectiveness of ignition interlocks while installed.

22Individuals may still be arrested for DWI while they have an interlock installed in their 

vehicle, for instance if they remove the device, or if they are driving a vehicle that does not 

have an interlock installed in it. 

23The authors of this study attributed the difference in reductions in risk of re-arrest 

between the first and second randomized controlled trials to monitoring and length of 

installation, which will be discussed further below. 
 

Page 13 GAO-14-559 Traffic Safety

pre-interlock rates.24 For example, a study of drivers with two or three 

DWI offenses in New Mexico observed a reduction in re-arrest while the

ignition interlocks were installed, but in a period following removal of the 

ignition interlock, there was no significant difference in DWI re-arrest rates 

between offenders who had installed the ignition interlock and those who 

had not. The literature review of 15 studies came to the same conclusion 

that, following removal of ignition interlocks, re-arrest rates reverted to 

levels similar to those for comparison groups.

Although ignition interlocks have been shown to reduce arrest for alcoholimpaired driving while installed, researchers we interviewed estimated 

that only 10 percent or less of DWI offenders ordered to install an ignition 

interlock actually install one.25 NHTSA officials reported that between 15 

and 20 percent of offenders arrested for DWI install ignition interlocks. 

Estimates in individual states vary, with one study of DWI offenders in 

California reporting about a 20 percent installation rate among those 

ordered to install.26

However, estimating installation rates is imprecise. Federal officials told 

us that it is difficult to accurately estimate installation rates because the 

underlying data is often inconsistently maintained within and across 

states. For example, NHTSA officials told us that in an ongoing study of 

state ignition-interlock programs, they were able to identify only eight 

states with sufficient data (e.g., the number of ignition interlocks ordered 

and the number of DWI offenders who actually installed the ignition 

interlocks) to estimate the program’s installation rate. As such, instead of 

using the number of individuals ordered to install an ignition interlock, one 

research group we spoke to used more easily-identifiable data such as 

total population, total DWI arrests, or total DWI fatalities. The resulting 

A recent evaluation completed for the Washington 

Traffic Safety Commission reported 56 percent of DWI offenders ordered 

to install an ignition interlock did so.

 

24One of the Maryland studies mentioned above showed decreases in re-arrest rates once 

the ignition interlocks were removed. 

25NHTSA officials noted that they suspected that this estimate is based on gross-level 

figures and is less accurate than the higher estimates.

26In the California study, offenders ordered to install an ignition interlock may have 

included both those convicted of DWI and of lesser Driving-While-Suspended charges. 

Several Factors Contribute 

to Low Installation Rates
 

Page 14 GAO-14-559 Traffic Safety

measure is referred to as an installation “in-use” rate—for instance, the 

number of ignition interlocks in-use as a percentage of total population.

According to state officials, limited follow up and monitoring for 

compliance and prerequisites for eligibility can hinder installation.

Limited follow-up and monitoring for offender compliance—According to 

the literature review cited above, monitoring DWI offenders requires 

substantial administrative resources. Officials from several states 

included in our study said they do not have sufficient resources to follow 

up with offenders to ensure ignition interlocks have been installed once 

they have been ordered by a court or sanctioned by a state department of 

motor vehicles. For example, state officials in Texas told us that courts 

(i.e., judges) are often overwhelmed and do not have the resources to 

follow up with offenders to ensure that an ignition interlock has been 

installed or to monitor the results gathered by the ignition interlock 

devices. According to New York officials, the caseloads of some 

probation officers who may supervise DWI offenders are also heavy, and 

some probation officers may not necessarily prioritize ignition interlock 

compliance. Other law enforcement entities, even those that may lead or 

operate the state’s ignition-interlock program, may not have the resources 

to follow up on offenders to ensure ignition interlocks have been installed 

and used as required. For example, Washington’s program is overseen 

by the state highway patrol, but according to a senior Washington official, 

the program lacks the resources to identify offenders who may be illegally 

driving with a suspended license (i.e., those offenders who claim to be 

waiting out the period of time that their license was suspended by not 

driving at all) or driving without an ignition interlock. 

Moreover, state officials we interviewed stated that limited followup and 

monitoring contributed to offenders’ decisions to wait out ignition interlock 

requirements. As mentioned above, the likelihood of being stopped for a 

traffic violation is estimated to be less than 1 percent of those driving 

while impaired by alcohol and research suggests that DWI offenders 

continue to drive while their licenses are suspended. Officials from New 

York described that a continuing challenge to increasing the number of 

installed interlocks were DWI offenders attempts to wait out the period an 

ignition interlock is required by temporarily signing over their vehicles to 

friends or family. According to these officials, in New York, quarterly 

inquiries are made to each of 62 counties’ probation departments to 

check vehicle registrations of DWI offenders to address such attempts to 

circumvent the state’s requirements for ignition interlocks. According to an 

Illinois official, there is no requirement that an offender install an ignition 
 

Page 15 GAO-14-559 Traffic Safety

interlock in order to reinstate his or her license27

Prerequisites for eligibility—There are a variety of conditions a DWI 

offender may be required to satisfy before he or she can receive interlockrestricted driving privileges.

and that requirements for 

interlock-restricted driving were undermined because many DWI 

offenders believed that they could avoid being caught while driving 

without an ignition interlock.

• Fees and penalties—In some states, offenders may have to pay fees 

and penalties before they can be eligible to install an ignition interlock 

and receive a restricted license. One study of Florida’s ignitioninterlock program found that half of DWI offenders who had completed 

their revocation period were still ineligible to install an ignition interlock 

because they had not paid required fines and tickets. Similarly, an 

Illinois official stated that a DWI offender would have to pay at least a 

$380 fee in addition to any outstanding fees or penalties and enter 

into a payment plan for any judgments resulting from the DWI 

conviction in order to be eligible for interlock-restricted driving 

privileges. Likewise, Connecticut requires offenders to pay a $100 fee 

before an ignition interlock is installed. These fees and penalties are 

in addition to any costs paid to the vendor for installation or lease of 

the interlocks. Even in some states where there are indigent funds 

available to assist offenders with the cost of ignition interlocks, some 

of these fees imposed by the state may not be waived or reduced.28

 

27This contrasts with a state like Washington, where an offender must have an interlock 

installed and have a certain number of consecutive months without BAC tests registering 

above the predetermined level in order for their license to be reinstated.

In 

Texas, one official described how mandatory license surcharges have 

contributed to a substantial number of offenders driving illegally and 

without insurance.

28For example, in Washington, an offender seeking interlock-restricted driving privileges 

must pay $100 to apply for reinstatement. However, if he or she qualified for assistance 

from Washington’s indigent fund, this assistance may only be used for vender fees (i.e., 

costs associated with ignition-interlock installation, lease, removal, and transfer to another 

vehicle) and not for the application fee. Furthermore, some states with indigent funds have 

experienced challenges with the demand for this assistance. Washington officials stated 

that the number of interlock drivers receiving support from the indigent fund grew from 

3,066 in 2009 to 19,267 by December 2013, and the amount disbursed increased from 

$775,643 to more than $1.4 million between 2011 and 2013. Washington officials said that 

the number of applicants was beginning to exceed available funds. 
 

Page 16 GAO-14-559 Traffic Safety

• Treatment programs—In some states, offenders must complete 

treatment programs before they are eligible to install an interlock and 

have interlock-restricted driving privileges. In Illinois, offenders may be 

required by a hearing officer or judge to enter or complete treatment,

in conjunction with installing an interlock, as conditions for being 

granted a restricted drivers license. Likewise, in New York, officials 

noted that some jurisdictions will not allow offenders to obtain their 

licenses until treatment has been completed.

Research supports the effectiveness of ignition interlocks in combating 

impaired driving while they are installed, but limited research exists on 

how to improve installation rates.

Table 2: Summary of Ignition-Interlock Effectiveness Research 

Effectiveness research topic

Substantial 

research

Limited 

research a Ongoing, unpublished 

studies a

Interlock Devices

Effective when installed X 

Effect disappears when interlock is removed X 

Interlock Programs

Characteristics that could increase installation

• harsher alternatives

, such as:

• requiring an interlock for license reinstatement

X Xb

Characteristics that could 

 (NHTSA) 

reduce re-arrest during and after 

• length of installation

installation, such as:

• combining treatment with the interlock program

• monitoring

X X (NHTSAb

, CDCc

Source: GAO. | GAO-14-559 

) 

a

We refer to research as “substantial” if we identified five or more articles published on the topic 

whose results we determined to be reliable. We refer to research as “limited” if we identified fewer 

than five articles published on the topic whose results we determined to be reliable.

b

NHTSA has a cooperative agreement with GHSA, which contracted with the Preusser Research 

Group to evaluate state ignition interlock use and re-arrest rates in 28 states. NHTSA expects these 

studies to be published by 2015.

c

Limited Research Exists 

on Which Program 

Characteristics Could 

Improve Installation or 

Overall Program 

Effectiveness

The Centers for Disease Control and Prevention (CDC) is currently analyzing the effect of treatment 

on re-arrest. The CDC expects to publish this study in 2015 at the earliest.
 

Page 17 GAO-14-559 Traffic Safety

Two studies of programs in U.S. counties where judges required stricter 

penalties for those not installing an ordered ignition interlock found a 

higher percentage of offenders installed the ignition interlock. According 

to a 2001 study, a court in Hancock County, Indiana, had required 

installation of interlocks for all offenders using the threat of jail or 

electronically monitored house arrest for non-compliance since 1997. The 

study estimated that 62 percent of DWI offenders installed an ignition 

interlock.29 A 2010 NHTSA evaluation of the New Mexico ignition-interlock 

program found that 71 percent of convicted DWI offenders installed an 

interlock in Santa Fe County, where judges made house arrest the 

alternative to ignition interlock installation. In cases where DWI offenders 

pleaded they had no vehicle, the judge required them to wear an 

electronic monitoring bracelet.30

One study suggested that requiring an ignition interlock for license 

reinstatement following a DWI could improve installation rates. As 

mentioned above, one of the ways a DWI offender can avoid installing an 

interlock is by simply waiting out the ordered suspension period and not 

driving during that time. Yet research suggests that many DWI offenders 

drive during a suspension period.

According to a 2013 MADD report based 

on workshops with state officials and stakeholders from more than 30 

states, imposing harsher sanctions could be a strategy for increasing 

installation rates. One state official we interviewed described that 

mandating alcohol monitoring as an alternative to installing an interlock 

would be effective in increasing the installation rates.

31

 

29This refers to the percentage of offenders who installed interlocks, not the additional 

percentage attributable to Hancock County’s program; the authors did not measure the 

rates of interlock installation in the surrounding counties, so we cannot isolate the effect of 

Hancock County’s stricter program. In addition, the 95 percent confidence interval for this

installation rate extends from roughly 50 percent to 74 percent. 

However, if a state has a separate 

30An electronic monitoring bracelet is a device worn on an offender’s ankle that 

electronically tracks his or her location. In order to enforce house arrest, the bracelet is 

linked by telephone lines to a main computer system that sends off a constant signal. If 

the offender strays beyond the court-authorized radius of the receiver, the computer 

system records the date and time that the interruption occurred. If the interruption 

occurred at a time when the offender was scheduled to be at home, a parole officer or 

other monitoring agent checks into the violation and additional sanctions may result.

31Ignition-interlock studies cited in this report often use license suspension as the control 

group. As stated above, ignition interlocks are more effective than license suspension, 

which means that many DWI offenders continue driving and being re-arrested while their 

licenses are suspended. 

Characteristics That Could 

Increase Installation: Harsher 

Alternatives, License 

Reinstatement
 

Page 18 GAO-14-559 Traffic Safety

administrative requirement through the department of motor vehicles, for 

example, the offender cannot simply wait out the suspension period and 

will have to install an ignition interlock in order to reinstate his full license. 

A 2013 study on a Florida state requirement that DWI offenders install an 

ignition interlock for at least 6 months in order to fully reinstate their 

license observed that nearly 100 percent of offenders eligible to install an 

interlock actually did so.32

NHTSA is currently working with the Preusser Research Group (PRG) to 

conduct a study on factors that could help states improve installation 

rates. This research is being supported jointly by NHTSA and the CDC, 

through a cooperative agreement with GHSA, which in turn contracted 

with PRG to examine state ignition-interlock program characteristics—

such as state laws, penalties, monitoring, or other factors—that were 

associated with higher ignition interlock use. NHTSA officials said they 

expect this report to be issued by late summer 2014.

According to state officials, New Mexico and 

Washington have a similar license reinstatement requirement.

A randomized controlled trial of DWI multiple offenders in Maryland 

observed that closer monitoring of offenders’ breath tests into the 

interlock device improved compliance with the ignition-interlock program. 

Closer monitoring consisted of reviewing breath test data and sending 

letters to offenders informing them of the results and consequences. The 

control group was subject to the standard Motor Vehicle Administration 

monitoring, which did not include any specific procedures for monitoring 

offenders. For example, the Motor Vehicle Administration took no action 

when offenders in this group disconnected the interlock or logged 

numerous breath tests at or above the limit of the ignition interlock. The 

authors found that the closely monitored group had significantly fewer 

initial breath test failures when attempting to start their vehicles than the 

control group did. The authors also observed that ignition interlock 

disconnects (e.g., tampering with the device) and retest failures were 

lower for the closely monitored group as well, although these latter 

differences were not statistically significant. Through the GHSA study 

mentioned above, NHTSA officials told us that NHTSA and the CDC hope 

to identify state’s ignition-interlock program characteristics, such as 

 

32Many offenders were not eligible to install an interlock during the time of the study. In 

Florida, as noted above, offenders must complete outstanding sanctions (e.g., tickets, 

fines) before being eligible to install an ignition interlock. 

Characteristics That Could 

Reduce Re-arrest during and 

after Interlock: Monitoring, 

Length of Installation, and 

Treatment
 

Page 19 GAO-14-559 Traffic Safety

monitoring, that may be associated with lower re-arrests. NHTSA officials 

said this study should be completed by 2015.

We identified one study on the impact of varying lengths of ignitioninterlock installation on DWI re-arrest. The study compared the results of 

the Maryland’s two randomized controlled trials mentioned above (2011 

and 1999) in order to determine whether the later 2-year administrative 

ignition-interlock program was more effective in reducing recidivism than 

the earlier 1-year interlock program. The 2011 study did show a 

significant reduction in re-arrest even after the interlock was removed, a 

result that the authors attributed to the extension of the interlock period 

from 1 year to 2 years, although other differences in the two randomized 

controlled trials, such as increased monitoring, were noted as well.33

According to researchers, pairing interlock use with alcohol treatment 

could be key to reducing re-arrest once the interlock is removed, but we 

did not find any published studies evaluating the combination of interlock 

use with treatment programs. Four studies in our review observed the 

drinking patterns of DWI offenders while they participated in an ignitioninterlock program, and two of these suggested that this data could be 

used to target treatment to specific offenders.

Despite this research, authors of the literature review mentioned above 

noted that research currently provides little guidance on the ideal length 

of interlock program participation. Research and interviews we conducted 

suggests that most states require installation for at least 5 months.

34

 

33A 2014 Washington state report on its ignition-interlock program observed reductions in 

re-arrest for DWI during a 2-year period following ignition interlock installation, and 

hypothesized that this could have been due to longer installation periods, among other 

factors. The study observed differences in re-arrest rates for first, second, and third-plus 

DWI offender groups whose installation periods averaged 10.4, 13.3, and 13.8 months, 

respectively. However, the study was not designed to evaluate the impact of length of 

installation. 

This has led researchers 

and NHTSA officials to posit that treatment could reduce the overall 

amount of drinking and potentially have an effect even after the ignition 

interlock is removed. The CDC is currently conducting a study on the 

34Authors of two of these studies, conducted in Canada, noted that the BAC results 

cannot be matched directly to the offender, but believe this limitation is mitigated by 

findings from other studies that show that primarily the offenders are the ones driving the 

interlocked vehicles. Authors of the other two studies noted that the vendor data they used 

contained no demographic information and so they were not able to distinguish between 

types of offenders.
 

Page 20 GAO-14-559 Traffic Safety

effect of a Florida state law that required alcohol treatment for DWI 

offenders who fail a certain number of breath tests on their installed 

ignition interlocks. CDC officials told us the results of this study would be 

published in 2015 at the earliest.

NHTSA offered a variety of assistance—including guidance, technical 

assistance, research, and education—to help states establish and 

improve their ignition-interlock programs, including the new ignitioninterlock grant established by MAP-21. State officials who administered 

ignition-interlock programs confirmed that NHTSA’s activities were 

helpful. However, some officials questioned NHTSA’s implementation of 

the ignition-interlock grant program because the states that exempted 

certain offenders from installing interlocks were disqualified. According to 

some state officials, exemptions are seldom used in practice, but are 

important to maintain because they facilitate the ability of offenders to 

work.

NHTSA offered a variety of assistance to help states establish and 

improve their ignition-interlock programs. Specifically, NHTSA developed 

and shared guidance, issued technical specifications, sponsored research 

studies, collaborated with industry experts, and funded technical 

assistance. It also administered and oversaw grants to states.

• Guidance: Since 2008, NHTSA has published reports highlighting 

key features of state ignition-interlock programs, including most 

recently the 2013 guideline for a model ignition-interlock program.35

• Technical Specifications: In 1992, NHTSA published technical 

model specifications for ignition interlocks that describe how ignition 

interlock devices should perform and indicate how they can be 

calibrated to meet uniform standards. In May 2013, NHTSA revised 

the model specifications to address the rapid technological 

In 

general, these reports provide information about ignition-interlock 

program features and highlight issues that states should consider as 

they put together or further refine their ignition-interlock programs.

 

35U.S. Department of Transportation, National Highway Traffic Safety Administration, 

Model Guideline for State Ignition-interlock Programs, Report Number DOT HS 811 859 

(December 2013).

NHTSA Provided 

Assistance to States 

for Ignition-Interlock 

Programs, but Some 

State Officials 

Questioned NHTSA’s 

Implementation of 

MAP-21 Grant

NHTSA Assisted States in 

Their Efforts to Implement 

Ignition-Interlock 

Programs
 

Page 21 GAO-14-559 Traffic Safety

innovations in the industry that had occurred since the original 

publication. State ignition-interlock program administrators used these 

model specifications to certify interlock devices offered by 

manufacturers and ensure vendors and installers meet uniform 

performance standards.

• Research: NHTSA funds research studies that assess and provide a 

more scientific basis for assertions about the effectiveness of ignition 

interlock devices. Since 2009, NHTSA has funded and published a 

number of studies and reports on ignition interlocks, including the 

ongoing studies mentioned above on factors that could help states 

improve installation rates or program characteristics related to lower 

re-arrest rates.

• Collaboration: NHTSA, either directly or through grants to other 

organizations, brought stakeholders and experts together to share 

information and collaborate on specific ignition-interlock program 

projects. For example, in 2007, NHTSA funded an expert panel to 

gather views about the effectiveness of ignition interlocks in 

preventing impaired driving offenses; the views were published in a 

2010 NHTSA report. In 2010, NHTSA and GHSA jointly hosted a 

national ignition interlock summit, extending invitations to state 

highway safety representatives and ignition-interlock program 

administrators from all 50 states, interlock manufacturers, 

researchers, and national organizations. NHTSA published a report 

summarizing the summit in 2011. NHTSA also signed a cooperative 

agreement with MADD for the organization to hold a series of ignition 

interlock institutes across the U.S. between August 2009 and October 

2012. The institutes were designed to bring together teams of people 

and various agencies that are involved with some component of their 

state ignition-interlock program in order to identify program 

improvements.

• Technical Assistance: In 2007, NHTSA entered into the first of two 

cooperative agreements with TIRF to support the development of a 

curriculum about ignition-interlock programs and to provide direct 

assistance to states that seek to improve their ignition-interlock 

programs. At the request of a state’s highway safety office, TIRF 

consultants review the state’s ignition-interlock program, analyze the 

program’s processes, and identify possible solutions for any 

weaknesses. For example, in 2009, TIRF examined Illinois’ ignitioninterlock program and identified a number of program strengths and 

challenges. TIRF recommended that the state develop a process for 

limiting the number of offenders who can opt out of the interlock 

program, among other things. NHTSA’s cooperative agreement with 

TIRF to provide technical assistance ends in August 2017.
 

Page 22 GAO-14-559 Traffic Safety

• Grants Administration: NHTSA also assisted state officials to apply 

for DOT safety grants, such as the impaired driving countermeasures 

grant, that can be used for their state’s ignition-interlock program. For 

example, the agency held webinars and conducted other outreach to 

educate states about the requirements of the new ignition-interlock 

grant program.

State officials indicated that NHTSA’s actions assisted them in 

implementing and further refining their ignition-interlock programs. For 

example, two state officials noted that by attending conferences 

sponsored by NHTSA they were able to leverage the experiences of other 

states whose programs were more mature. Others noted that NHTSA’s 

regional staff were readily available to answer questions and provide 

advice and technical assistance. State officials also mentioned that they 

used NHTSA’s ignition-interlock reports and guidance, such as the 2013 

Model Guidelines report, to identify ways to strengthen their programs.

State officials questioned how NHTSA implemented one aspect of the 

new ignition-interlock grant program; specifically that states did not qualify 

for funding if they included exemptions in their alcohol ignition-interlock 

programs. As described previously, states qualify for this grant by 

requiring that all individuals convicted of a DWI offense be limited to 

driving motor vehicles equipped with an ignition interlock. Under NHTSA’s 

implementation regulations, states must require that the ignition interlock 

be used for a minimum period of 30 days. As implemented by NHTSA, 

states whose ignition-interlock programs allowed DWI offenders to drive 

vehicles without an ignition interlock for work and medical reasons did not 

qualify for the grants because their programs were not considered 

mandatory for all such convicted individuals. Officials from New York, 

Illinois, Washington, and Arizona indicated that NHTSA disqualified their 

state because of the employer vehicle exemptions to their state’s ignitioninterlock requirements. Illinois and New York officials stated that although 

their state’s statutes allow exemptions, their programs typically grant few 

exemptions compared to the number of ignition interlocks installed, and 

the officials did not believe that exemptions substantially diminished the 

effectiveness of their ignition-interlock program. However, state officials 

noted they did not track the specific number of employer vehicle 

exemptions that have been granted. For example, in New York, employer 

vehicle exemptions are filed at the county level, not at the state level (i.e., 

with a state level department), and the state has little ability to access the 

data in order to estimate the number of employer vehicle exemptions that 

Some State Officials 

Questioned NHTSA’s 

Implementation of the New 

Grant
 

Page 23 GAO-14-559 Traffic Safety

had been granted or compare this to the number of ignition interlocks 

ordered.

NHTSA officials stated that they based their implementation of the 

ignition-interlock grant on the plain meaning of the authorizing language 

in MAP-21, which did not include any reference to exemptions or 

exclusions.36 In responding to our draft report, the Department of 

Transportation (DOT) provided a document that contained information on 

states’ ignition-interlock laws.37 Specifically, NHTSA’s Digest indicated 

that as of May 2012 at least 5 states allowed exemptions for employer 

vehicles, and additional states had other factors that would prevent them 

from qualifying for the ignition-interlock grant. NHTSA officials noted that 

the MAP-21 grant represents a high bar for many states. Based on 

experience in reviewing state impaired driving laws, NHTSA officials 

recognized that many states would have to change existing laws to apply 

to first time offenders and eliminate exemptions. Few states were 

expected to qualify in the grant’s first years because it would be difficult 

for state legislatures to change their ignition interlock laws in that time 

frame. Further, NHTSA officials noted that the agency did not receive 

comments from states related to exemptions during the public comment 

period for the interim final rule.38

Some state officials noted that it would be challenging to change their 

laws to qualify for the ignition-interlock grant. First, officials from several 

states told us that there is a lack of political support to put in place 

requirements for first time offenders or to eliminate exemptions. State 

officials from two states reported that their legislatures would not want to 

impede employment of offenders, particularly in a poor economic climate 

 

36Statutory construction includes and often begins with construing the “plain meaning” of 

the statutory language itself to determine whether the language at issue has a plain and 

unambiguous meaning. 

37DOT periodically compiles and publishes comprehensive information on state impaireddriving laws in its Digest of Impaired Driving and Selected Beverage Control Laws. DOT 

officials stated that they anticipate updating the publication in 2016 or 2017. See U.S. 

Department of Transportation, National Highway Traffic Safety Administration, Digest of 

Impaired Driving and Selected Beverage Control Laws, 27th Edition, Report Number DOT 

HS 811 796 (May 2012).

38NHTSA officials also noted that exemptions in any form can undermine the intended 

benefits of traffic safety laws and allowing offenders to drive without ignition interlocks 

through the use of exemptions could negatively impact traffic safety. 
 

Page 24 GAO-14-559 Traffic Safety

and given the expanse of areas in states that are rural, which makes 

driving a necessity for daily life. Some state officials also pointed out that 

the small size and short term nature of the grant funding did not support 

making changes to their states’ ignition-interlock programs to qualify for 

the MAP-21 ignition-interlock grant program.

Despite these challenges, two state legislatures changed their laws to 

eliminate exemptions to qualify for the ignition-interlock grant in fiscal year 

2014. During the first year of the grant—fiscal year 2013—only 2 states 

out of 14 that applied qualified for the grant. Most of the states that did not 

receive the grant were disqualified due to employer exemptions. State 

legislatures in Arizona and Washington39 were able to eliminate employer 

exemptions and other disqualifying factors from their laws in order to 

qualify for the grant in fiscal year 2014, bringing the total grant recipients 

to four that year. Because the ignition-interlock grant is relatively new, the 

extent to which additional state legislatures would be willing or able to 

modify their laws to qualify for the grant is unclear.

Ignition interlocks are one promising tool states can use to combat 

alcohol-impaired driving. However, in order to be effective, the devices 

must first be installed in vehicles and several factors—including limited 

monitoring and eligibility prerequisites—can hinder installation even when 

DWI offenders are ordered to use ignition interlocks. Ongoing and 

planned research by NHTSA and others may shed light on actions state 

officials can take to increase installation rates and otherwise improve the 

effectiveness of their ignition-interlock programs. The MAP-21 ignitioninterlock grant also has the potential to encourage the increased use of 

ignition interlocks by providing funds to states that require the use of an 

ignition interlock for all individuals convicted of a DWI offense. In the first 

2 years of the grant program, few states applied for the grant and of 

those, most were disqualified because of exemptions that allowed DWI 

offenders to drive employer-owned vehicles without ignition interlocks. 

Following the first grant year, two state legislatures modified their state 

ignition-interlock laws to eliminate employer and other exemptions, 

thereby qualifying for the MAP-21 grant in 2014. The extent to which 

 

39Washington changed its laws so that employer exemptions could not be used in the first 

30 days after a convicted DWI first-time offender is limited to interlock-restricted driving. 

For repeat offenders, employer exemptions may not be used for the first 365 days of 

interlock-restricted driving.

Concluding 

Observations
 

Page 25 GAO-14-559 Traffic Safety

other states may follow suit is unclear. Some state officials noted that 

even though these exemptions are not widely used, this option is critical 

to allow DWI offenders to retain their jobs, particularly in rural areas or 

areas without public transportation. For such states, the incentive and 

relatively limited funding offered by the grant is not likely to outweigh the 

challenges of changing state ignition-interlock laws to eliminate 

exemptions. 

We provided a draft of this report to DOT for review and comment. 

Included in the draft report was a recommendation that the Secretary of 

Transportation provide Congress with information about the extent to 

which states’ ignition interlock laws allow exemptions. This 

recommendation was intended to provide Congress with more complete 

information as it considers reauthorizing surface transportation programs, 

including the ignition-interlock grant program. On June 11, 2014, the 

Deputy Director of Audit Relations transmitted DOT’s comments by email. 

In responding to our draft report, DOT officials expressed concerns about 

this recommendation and provided additional information that addressed 

our recommendation. Specifically, DOT provided the Digest of Impaired 

Driving and Selected Beverage Control Laws, which is a compilation of 

comprehensive information on states’ impaired-driving laws. We 

concluded that the Digest includes sufficient information to provide an 

overview of the extent to which state laws allow exemptions and 

addresses our proposed recommendation. Therefore, in light of the new 

information that DOT provided, we withdrew our recommendation. DOT 

also provided technical corrections, which we incorporated as 

appropriate. 

As agreed with your office, unless you publicly announce the contents of 

this report earlier, we plan no further distribution until 30 days from the 

report date. At that time, we will send copies to the appropriate 

congressional committees, the Secretary of Transportation, and other 

interested parties. In addition, the report will be available at no charge on 

the GAO website at http://www.gao.gov. 

Agency Comments
 

Page 26 GAO-14-559 Traffic Safety

If you or your staff have any questions about this report, please contact 

me at (202) 512-2834 or flemings@gao.gov. Contact points for our 

Offices of Congressional Relations and Public Affairs may be found on 

the last page of this report. GAO staff who made key contributions to this 

report are listed in appendix III.

Sincerely yours, 

Susan A. Fleming

Director, Physical Infrastructure Issues
Appendix I: Objectives, Scope, and 

Methodology

Page 27 GAO-14-559 Traffic Safety

The objectives of our review were to determine (1) what is known about 

the effectiveness of ignition interlocks in reducing alcohol-impaired driving 

and (2) the extent to which the National Highway Traffic Safety 

Administration (NHTSA) has assisted states in implementing ignitioninterlock programs, including the Moving Ahead for Progress in the 21st 

Century Act (MAP-21) ignition-interlock grant program.

To identify what is known about the effectiveness of ignition-interlock 

programs, we conducted a literature search for studies that analyzed 

relationships between ignition interlock devices or programs and alcoholimpaired driving outcomes, including DWI arrest and DWI fatality. We 

started with a 2010 NHTSA report “Key Features for Ignition Interlock 

Programs,” which cited 15 studies and highlighted programs and program 

features that are believed to be best able to serve traffic safety interests, 

including reducing alcohol-impaired driving. We then identified additional 

existing studies from peer-reviewed journals, government reports, and 

conference papers based on searches of various databases, such as 

ProQuest, MEDLINE, and Transportation Research International 

Documentation. Search parameters included studies across the U.S. and 

in specific states and those on specific interlock program components, 

such as mandatory for first and repeat offenders and length of installation 

required. These parameters resulted in 280 abstracts, which we narrowed 

to 96, in part by cross-referencing the list with Web of Science, a resource 

that identifies highly cited articles. We also conducted interviews with 

organizations that conduct research on ignition interlocks, such as the 

Pacific Institute for Research and Evaluation, and asked them to 

recommend additional research.

From these multiple sources, we identified 25 peer-reviewed articles, 

government reports, and conference papers between 1990 and 2013 that 

were relevant to our research objective on the effectiveness of ignition 

interlocks in reducing alcohol-impaired driving. To assess the 

methodological quality of the selected studies, we performed an initial indepth review of the findings, and then a GAO methodologist performed an 

independent assessment of the study’s methodological soundness and 

confirmed our reported analysis of the finding. One limitation is that the 

majority of studies we identified did not randomly assign participants to 

the ignition interlock; therefore there remains the potential for selection 

bias, as individuals who agree to install an interlock may be inherently 

different from individuals who do not agree. Additional limitations related 

to the body of literature we reviewed include the lack of a national study 

on interlock effectiveness, a lengthy time period over which the studies 

were conducted (between 1990 and 2013), and the reliance of DWI arrest 

Appendix I: Objectives, Scope, and 

Methodology
Appendix I: Objectives, Scope, and 

Methodology

Page 28 GAO-14-559 Traffic Safety

as a proxy for alcohol-impaired driving. Despite these limitations, our 

review of the literature did provide support for the effectiveness of ignition 

interlocks while installed.

We supplemented our synthesis by interviewing three of the studies’ 

authors who had each contributed to multiple studies. We also conducted 

interviews with NHTSA officials, as NHTSA has contracted out some 

published and ongoing research on the effectiveness of ignition 

interlocks. We also discussed program effects with state ignition-interlock 

program administrators from the 10 states we included in our review (as 

discussed below) and with NHTSA officials who were knowledgeable 

about NHTSA-funded published and ongoing research on the 

effectiveness of ignition interlocks.

To identify the types of assistance that NHTSA provides to states to help 

them establish and implement their ignition-interlock programs, we 

interviewed NHTSA officials about their activities and reviewed reports 

describing NHTSA’s ignition interlock-related research, technical 

assistance, and conferences. For both objectives, we interviewed 

representatives from safety advocacy organizations such as the 

Governors Highway Safety Association and Mothers Against Drunk 

Driving. We also interviewed traffic safety, criminal justice, department of 

motor vehicles or licensing, and law enforcement officials from a 

nongeneralizable sample of 10 states. The selected states—Arizona, 

Connecticut, Illinois, Montana, New Mexico, New York, Pennsylvania, 

South Carolina, Texas, and Washington—were chosen to reflect a mix of 

states that applied and did not apply for, as well as, states that qualified 

and were disqualified from the MAP-21 ignition-interlock grant program. 

To further select among states, we identified states with high DWI fatality 

numbers in 2012 (the most recent year for which data are available) and 

DWI fatality rates (alcohol-impaired fatalities per 100-million vehicle-miles 

traveled) as calculated and categorized by NHTSA as high-, mid-, and 

low-range states. We also factored in different types of programs 

(judiciary, administrative, and hybrid); states with low DWI fatalities or 

rates; and states with rural areas and tribal authorities, in selecting our 

state sample.

Although the information gathered from these 10 states are 

nongeneralizable, it provided insights about the extent of NHTSA’s 

ignition interlock-related assistance, including its implementation of MAP21 ignition-interlock grant program, and the ignition interlock-related 

research that states had conducted or participated in. In each state, we 

obtained information about the state’s ignition interlock laws and program 
Appendix I: Objectives, Scope, and 

Methodology

Page 29 GAO-14-559 Traffic Safety

as well as any challenges in applying or qualifying for the MAP-21 

ignition-interlock grant program. We also asked state officials about 

NHTSA’s other ignition-interlock related assistance.

We conducted this performance audit from July 2013 to June 2014 in 

accordance with generally accepted government auditing standards, 

Those standards require that we plan and perform the audit to obtain 

sufficient, appropriate evidence to provide a reasonable basis for our 

findings and conclusions based on our audit objectives. We believe that 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives. 
Appendix II: Studies on Ignition-Interlock 

Effectiveness

Page 30 GAO-14-559 Traffic Safety

Beck, Kenneth H., William J. Rauch, Elizabeth A. Baker, and Alian F. 

Williams. “Effects of Ignition Interlock License Restrictions on Drivers With

Multiple Alcohol Offenses: A Randomized Trial in Maryland.” American 

Journal of Public Health 89(11) (1999): 1696-1700.

Bjerre, Bo. “Primary and secondary prevention of drinking and driving by 

the use of Alcolock device and program: the Swedish experience,” in 

Alcohol Ignition Interlock Devices, Volume II: Research, Policy, and 

Program Status 2005. ed. Paul Marques (Oosterhout, Netherlands: 

International Council on Alcohol, Drugs and Traffic Safety (ICADTS), 

2005), 11-24.

Coben, Jeffrey H., and Gregory L. Larkin. “Effectiveness of Ignition 

Interlock Devices in Reducing Drunk Driving Recidivism.” American 

Journal of Preventive Medicine, 16(1S) (1999): 81-87.

DeYoung, David J., Helen N. Tashima, and Scott V. Masten. “An 

Evaluation of the Effectiveness of Ignition Interlock in California” in 

Alcohol Ignition Interlock Devices – Volume II: Research, policy, and 

Program Status 2005. ed. Paul Marques (Oosterhout, Netherlands: 

International Council on Alcohol, Drugs and Traffic Safety (ICADTS), 

2005), 42-52.

Elder, Randy W., Robert Voas, Doug Beirness, Ruth A. Shults, David A. 

Sleet, James L. Nichols, and Richard Compton, Task Force on 

Community Preventive Services. “Effectiveness of Ignition Interlocks for 

Preventing Alcohol-Impaired Driving and Alcohol-Related Crashes. A 

Community Guide Systematic Review.” American Journal of Preventative 

Medicine 40(3) (2011): 362-376.

EMT Group. “Evaluation of the California ignition interlock pilot program 

for DUI offenders.” A report prepared for The California Department of 

Alcohol and Drug Programs and The California Office of Traffic Safety, 

1990.

Jones, Barnie. “The Effectiveness of Oregon’s Ignition-interlock program.” 

Paper presented at the 12th International Conference on Alcohol, Drugs, 

and Traffic Safety, Cologne, Germany, September 28-October 2, 1992.

Marine, William. “High-tech solutions to drinking and driving: evaluation of 

a statewide, voluntary alcohol ignition-interlock program.” Final grant 

report. University of Colorado Health Sciences Center (2001).

Appendix II: Studies on Ignition-Interlock 

Effectiveness
Appendix II: Studies on Ignition-Interlock 

Effectiveness

Page 31 GAO-14-559 Traffic Safety

Marques, Paul R., A. Scott Tippetts, and Robert B. Voas. “Comparative 

and joint prediction of DUI recidivism from alcohol ignition interlock and 

driver records.” Journal of Studies on Alcohol, 64(1) (2003): 83-92.

Marques, Paul R., Robert B. Voas, Richard Roth, and A. Scott Tippetts. 

Evaluation of the New Mexico Ignition-interlock program. A report 

prepared at the request of the National Highway Traffic Safety 

Administration, 2010.

Marques, Paul R., A. Scott Tippetts, and Robert B. Voas. “The Alcohol 

Interlock: An Underutilized Resource for Predicting and Controlling Drunk 

Drivers.” Traffic Injury Prevention, 4:S1 (2006): 5-11.

Morse, Barbara J. and Delbert S. Elliott. “Effects of Ignition Interlock 

Devices on DUI Recidivism: Findings From a Longitudinal Study in 

Hamilton County, Ohio.” Crime & Delinquency 38 (2) (1992): 131-157.

Popkin, Carol Lederhaus, J. Richard Stewart, Jo Beckmeyer, and Carol 

Martell. “An evaluation of the effectiveness of interlock systems in 

preventing DWI recidivism among second-time DWI offenders.” Paper 

presented at the 12th International Conference on Alcohol, Drugs, and 

Traffic Safety, Cologne, Germany, September 28-October 2, 1992.

Raub, Richard A., Rov E. Lucke, and Richard Wark. “Breath alcohol 

ignition interlock devices: controlling the recidivist.” Traffic Injury 

Prevention 4 (2003):199 –205.

Rauch, William J., Eileen M. Ahlin, Paul L. Zador, Jan M. Howard, and G. 

Doug Duncan. “Effects of administrative ignition interlock license 

restrictions on drivers with multiple alcohol offenses.” Journal of 

Experimental Criminology 7 (2011): 127-148.

Roth, Richard, Robert Voas, and Paul Marques. “Mandating Interlocks for 

Fully Revoked Offenders: The New Mexico Experience.” Traffic Injury 

Prevention, 8 (2007): 20-25.

Tippetts, A. Scott, and Robert B. Voas. “The effectiveness of the West 

Virginia interlock program.” Journal of Traffic Medicine 26 (1998):19-24.

Vanlaar, Ward, Anna McKiernan, and Robyn Robertson. “Behavioral 

Patterns of Interlocked Offenders: Phase II.” Traffic Injury Research 

Foundation (2013).
Appendix II: Studies on Ignition-Interlock 

Effectiveness

Page 32 GAO-14-559 Traffic Safety

Vanlaar, Ward, Robyn Robertson, Desirée Schaap, and Jan Vissers. 

“Understanding Behavioural Patterns of Interlocked Offenders to Inform 

the Efficient and Effective Implementation of Interlock Programs: How 

Offenders on an Interlock Learn to Comply.” Traffic Injury Research 

Foundation (2010).

Vezina, L. “The Quebec alcohol ignition-interlock program: impact on 

recidivism and crashes.” Proceedings of the 16th International 

Conference on Alcohol, Drugs and Traffic Safety, Montreal, Canada, 

August 4-9, 2002.

Voas, Robert B., Anthony S. Tippetts, and Milton Grosz. “Administrative 

Reinstatement Interlock Programs: Florida, A 10-Year Study.” Alcoholism: 

Clinical and Experimental Research 37(7) (2013): 1243-1251.

Voas, Robert B., Kenneth O. Blackman, A. Scott Tippetts, and Paul R. 

Marques. “Evaluation of a program to motivate impaired driving offenders 

to install ignition interlocks.” Accident Analysis and Prevention 34 (2002): 

449-455.

Voas, Robert B., Paul R. Marques, A. Scott Tippetts, and Douglas J. 

Beirness. “The Alberta interlock program: The evaluation of a provincewide program on DUI recidivism.” Addiction 94(12) (1999): 1849-1859.

Willis, C., S. Lybrand, and N. Bellamy. “Alcohol ignition-interlock 

programmes for reducing drink driving recidivism (Review). The Cochrane 

Database of Systematic Reviews (2004): 1-20.

Zador, Paul L., Eileen M. Ahlin, William J. Rauch, Jan M. Howard, and G. 

Doug Duncan. “The effects of closer monitoring on driver compliance with 

interlock restrictions.” Accident Analysis and Prevention 43 (2011): 1960-

1967.
Appendix III: GAO Contact and Staff 

Acknowledgments

Page 33 GAO-14-559 Traffic Safety

Susan A. Fleming, (202) 512-2834 or Flemings@gao.gov

In addition to the contact above, Sara Vermillion (Assistant Director); 

Melissa Bodeau; Russell Burnett; Leia Dickerson; Sarah Farkas; Geoffrey 

Hamilton; Kirsten Lauber; Gail Marnik; Josh Ormond; Friendly VangJohnson; and Elizabeth Wood made key contributions to this report.

Appendix III: GAO Contact and Staff 

Acknowledgments

GAO Contact

Staff 

Acknowledgments

(541110)
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