The Traffic Injury Research Foundation USA, Inc.
Traffic Injury Research Foundation USA, Inc. (TIRF USA) is an independent road safety research
institute that obtained 501(c)3 non-profit status in the US in 2014. The mission of TIRF USA is todevelop and share the knowledge that saves – preventing injuries and loss of life on the roads,
reducing related social, health and insurance costs, and safeguarding productivity.

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July 20202018 IGNITION INTERLOCKINSTALLATIONS: STATE DATA

Robyn D. Robertson, Hannah Barrett, Craig Lyon & Ward G.M. Vanlaar

Utah Department of Public Safety, Highway Safety Office Impaired Driving Program
Vermont Department of Motor Vehicles Ignition Interlock Unit
Virginia Commonwealth’s Attorneys’ Services Council, Traffic Safety Resource Prosecutor
The Commission on Virginia Alcohol Safety Action Program
Washington Traffic Safety Resource Prosecutor, Municipal Research Services CenterWest Virginia Division of Motor Vehicles Interlock Department
Wisconsin State Patrol, Chemical Test Section
Wyoming Department of Transportation, Driver Services

ACKNOWLEDGEMENTS
This study was conducted in partnership with the Association of Ignition Interlock Program
Administrators (AIIPA). The Traffic Injury Research Foundation USA, Inc. (TIRF USA) gratefully
acknowledges AIIPA for their partnership and cooperation.

TIRF USA also extends its gratitude to the following individuals for their guidance and advice ondata from the National Center for State Courts and state data in Arizona and Pennsylvania.
Sarah Gibson, Court Research Analyst, National Center for State Courts
Mark Stodola, Probation Fellow, American Probation and Parole Association
William A. Weiss, Esquire, Fritz & Bianculli, LLC
TIRF USA extends its appreciation to the following agencies that shared their time, knowledge andexpertise to contribute to this report.

National Center for State Courts

Arkansas Department of HealthArkansas Department of Finance and Administration, Office of Driver Services
California Department of Motor Vehicles Research and Development
Colorado District Attorneys' Council
Colorado Department of Revenue, Division of Motor Vehicles, Driver Control Section
Connecticut Department of Criminal JusticeConnecticut Department of Motor Vehicles, Office of Driver Services
Delaware Office of the Attorney General
Delaware Division of Motor Vehicles, Driver Improvement Program
Florida Department of Highway Safety and Motor Vehicles
Hawaii Department of Transportation Highway Safety
Iowa Department of Justice, Traffic Safety Resource Prosecutor
Iowa Department of Transportation, Driver Services-Records
Kansas Department of Revenue, Division of Vehicles
Maine Department of the Secretary of State, Bureau of Motor Vehicles, Driver License Services
Minnesota Department of Public Safety
Missouri Office of Prosecution Services
Missouri Department of Transportation, Traffic & Highway Safety Division
New York State Division of Criminal Justice Services
North Dakota Department of Transportation, Safety Division
Oregon Department of Transportation – Department of Motor Vehicles, Driver Control Program
Oregon Department of Transportation – Transportation Safety Division
Pennsylvania DUI Association Ignition Interlock Quality Assurance
Tennessee Department of Safety and Homeland Security, Tennessee Highway Patrol, Driver Services
Tennessee District Attorneys General Conference, Traffic Safety Resource Prosecutoriii

2014; no historical data were available for incoming DWI cases) 1, ultimately these data
revealed considerable room for growth in interlock installation rates within the US.

EXECUTIVE SUMMARY!

!

As of December 2019, 35 states and Washington, D.C. required all alcohol-impaired driving
offenders, including first offenders, to install an interlock device. There was a 3.6%
decrease in alcohol-impaired driving fatalities in 2018 from 2017 (National Center for
Statistics and Analysis 2019).

!

As of March 1st, 2020, data were received from 25 states and Washington, D.C.

!

Three measures were used in this study to measure trends in interlock installations:»

Total Installs Number (TIN): Total number of newly installed interlocks between
January 1st through to December 31st in a given year.

»

Total Installs Number all (TINall): Total number of interlocks installed in vehicles at
any time between January 1st through to December 31st in a given year, including
devices installed prior to January 1st but that were still in the vehicle for any period oftime during that year following January 1st.

»

Active Installs Number (AIN): Total number of interlocks in vehicles of active
participants on December 31st of a given year.

!

There were 145,202 new ignition interlock devices (TIN) installed in 18 states andWashington, D.C. in 2018. When comparing new interlock installations among the 12
states who provided TIN data for both 2016 and 2018 there was a 20% increase ininstallations from 65,967 in 2016 to 79,013 in 2018. Since 2014 there has been a 34%
increase in TIN according to data available from six states.

!

Based on TINall data, 223,223 installations were reported in 17 states and Washington,
D.C. in 2018. When comparing total installations among the 12 states who provided TINall
data for both 2016 and 2018 there was a 10% increase from 143,471 in 2016 to 158,283
in 2018. Previous data on TINall collected from manufacturers showed the number of
installations nationally was 614,626 in 2016 (Robertson et al., 2018). Applying the 10%
growth rate to this number results in an estimated 676,089 total installations nationally in
2018.

!

As of December 31st, 2018, there were 141,480 active installations (AIN) reported in 16
states. When comparing active installations among the 10 states who provided AIN data forboth 2016 and 2018 there was a 5% decrease from 110,159 in 2016 to 105,080 in 2018.
However, when comparing data from six states that provided this information since 2014,
there has been a 10% increase in AIN.

!

Among states where data were obtained, the percent of installations (TIN) per Driving while
Intoxicated or Impaired (DWI) arrests in 2018 was 48.41%, per 2018 DWI convictions it was
56.73% and per 2018 incoming DWI cases it was 37.57%. While the indicators for DWI
arrests and DWI convictions have consistently increased over time (17.5% and 35.3% in

1

iii

iv

In conclusion, the preponderance of the evidence shows considerable growth in theindustry yet confirms a relatively low installation rate among all eligible offenders.

Incoming DWI cases are defined as those added to the court’s caseload during the reporting period andinclude New Filing, Reopened, and Reactivated cases as per the definition of the National Center for State
Courts (cf. Methods section).

TABLE OF FIGURES AND TABLESTABLE OF CONTENTSMETHODS ................................................................................................................................. 4
Installation counts..................................................................................................................................... 4
Installation rates ....................................................................................................................................... 5

Figure 1: Laws mandating alcohol ignition interlock devices (December 2019) ............................... 2
Figure 2: Illustration of installation measures ................................................................................ 4
Figure 3: Total new installs (TIN) and active installed (AIN) devices as reported by six states in 20142016, 2018 ................................................................................................................... 9
Figure 4: Incoming DWI cases, 2014-2018 (source: National Center for State Courts) .................... 9
Figure 5: State arrests and DWI case data, 2018 ..........................................................................10
Figure 6: New interlock installations per DWI arrests and per convictions as a percentage in 20142016, 2018 ..................................................................................................................11

RESULTS .................................................................................................................................... 7
Number of new, total and active installed interlocks ............................................................................... 7
Impaired driving felony and misdemeanors ............................................................................................. 9
Installation rate of interlocks among eligible population of offenders .................................................. 10

Table 1: State reported installation data ....................................................................................... 7
Table 2: 2018 percentage of interlocks installed (TIN) per DWI arrests, per DWI convictions and perincoming DWI cases......................................................................................................12

ACKNOWLEDGEMENTS ............................................................................................................. i
EXECUTIVE SUMMARY .............................................................................................................iii
INTRODUCTION......................................................................................................................... 1

CONCLUSIONS .........................................................................................................................13
REFERENCES .............................................................................................................................15v

vi

Figure 1: Laws mandating alcohol ignition interlock devices (December 2019)2

INTRODUCTION
Unprecedented declines in the drinking driving problem occurred during the 1980s. Based on
declining trends in the percent of alcohol-related fatalities, progress continued through the 1990s,
although the gains were far less impressive (Simpson and Robertson 2001). In the new millennium,
data from the Fatality Analysis Reporting System (FARS) revealed alcohol-impaired driving fatalitiesin crashes involving drivers with a blood alcohol concentration (BAC) of at least .08 (the per se limit
in the US) declined by 27% from 13,582 in 2005 to 9,943 in 2014. Since 2014, increases havebeen noted in this indicator, e.g., in 2015 it increased to 10,265 (NHTSA August 2016). Morerecently, according to NHTSA, these alcohol-impaired driving fatalities accounted for 28.8% of
total motor vehicle crash (MVC) fatalities in 2018, or 10,511 lives lost, which is still higher than2014. Nevertheless, this corresponds to a 3.6% decrease compared to 2017 when the number offatalities was 10,908 (NHTSA October 2019). During the same time span vehicle miles traveled(VMT) increased by 0.3% from 2017 to 2018 and the overall fatality rate per 100 million VMTdecreased by 3.4 percent from 1.17 in 2017 to 1.13 in 2018.
Alcohol ignition interlock programs are an alcohol-impaired driving countermeasure proven to
reduce recidivism among both first and repeat offenders, including those who repeatedly drive
after drinking with extremely high BACs and are resistant to changing this behavior. A systematic
review of 15 scientific studies conducted by the Centers for Disease Control and Prevention (CDC)
revealed that while interlocks were installed, the re-arrest rate of offenders decreased by 67%
compared to groups that did not have the device installed (Elder et al. 2011). A study of New
Mexico’s interlock program showed offenders who participated in the program had a 61% lower
recidivism rate while the device was installed and a 39% lower recidivism rate following theremoval of the interlock compared to offenders who never had the device installed (Marques et al.
2010). Similar reductions were found by Vanlaar et al. (2017) when evaluating Nova Scotia’sinterlock program. A meta-analysis of interlock program evaluation studies conducted in 2005
found an average reduction of recidivism of 64% (Willis et al. 2004).

Despite the prevalence of interlock programs across the country, installation rates of interlocks
among eligible offenders vary considerably, and can be as low as approximately 15%. Given theevidence regarding interlocks, it is paramount they are utilized to the fullest by increasing
participation rates, and thereby ensuring this effective road safety measure is also an efficacious
one. It is therefore essential to monitor installation rates; such is the purpose of this data collection
effort.

Furthermore, recent evaluations studying the impact of interlocks on crashes have also
demonstrated interlock programs embedded in strong legislation can reduce alcohol-related
fatalities (Marques et al. 2010; McCartt et al. 2013; Kaufman and Wiebe, 2016; Lucas et al. 2016;
Vanlaar et al. 2017; McGinty et al. 2017; Teoh et al. 2018). Kaufman and Wiebe (2016) used datafrom 1999 to 2013 to compare alcohol-involved crash fatalities between 18 states with universal
mandatory interlock laws and 32 states without. Results indicated by installing interlocks on all new
vehicles, impaired driving fatalities would be reduced by 15%, and an estimated 2,500 lives would
be saved annually in the US. However, when given the sanction of a suspended license instead of
an interlock, more than half of convicted impaired driving offenders continue to drive and alcoholrelated crash rates are reduced by only 5% (Kaufman and Wiebe 2016).

The Traffic Injury Research Foundation USA, Inc. (TIRF USA) in partnership with the Association of
Ignition Interlock Program Administrators (AIIPA), and TIRF Canada collected data on interlock
installations in the US in 2018. Previous data collection for installations occurred in 2014, 2015,2016, and 2017 (Casanova Powell et al. 2016, 2017; Robertson et al. 2018). These data provide acomprehensive picture of interlock installations across the US and are a useful benchmark for state2

Alcohol-impaired driving offenders, including first offenders, were required to install an interlock
device in 35 states and Washington, D.C. as of December 2019 (Figure 1). An additional eightstates required interlocks for all first offenders with a BAC of .15 or greater, five states required
mandatory interlocks for all repeat offenders, and two states had discretionary or optional laws.

1

2

Source: MADD (2018). 2018 Report to the Nation. Mothers Against Drunk Driving (madd.org). The 2018
MADD figure was updated with individual state data obtained from the Highway Safety Offices for:California, Florida, Georgia, Indiana, Iowa, Kentucky, Massachusetts, Michigan Minnesota, Montana, New
Jersey, North Carolina, North Dakota, Ohio, Pennsylvania, South Carolina, South Dakota, Wisconsin,
Wyoming.

ignition interlock program administrators and impaired driving stakeholders to measure interlock
usage and growth in interlock programs on an annual basis. This report contains results from the2018 data collected from state agencies and compares these data to results from previous years. 3

METHODS
Installation counts
State alcohol ignition interlock program managers in all 50 states and Washington, D.C. were
contacted by email in October through December 2019 to request relevant ignition interlock datafor 2018. Three measures of installation were requested. Each indicator is useful to measure
growth, as well as to gauge workload associated with administering these programs. Specificdefinitions of these measures were provided as follows:!

Total Installs Number (TIN): Total number of newly installed interlocks between January
1st through to December 31st in a given year.

!

Total Installs Number all (TINall): Total number of interlocks in a vehicle at any time
between January 1st through to December 31st in a given year, including devices that may
have been installed prior to January 1st but were still in the vehicle for any period of time
during that year following January 1st.

!

Active Installs Number (AIN): Total number of interlocks in the vehicle of an active
participant on December 31st of a given year.

Figure 2 contains eight separate hypothetical interlock device installations to illustrate thesedefinitions for 2018. In this example, all installs (TINall) in 2018 is equal to eight, whereas new
installs (TIN) is four, and installs on December 31st, 2018 (AIN) is two.
Figure 2: Illustration of installation measures3

Due to the timing of data collection, the 2017 data year is missing. Future versions of this report may
include a completed time series, including the missing data year.

4At its core, there are two mechanisms driving growth in the interlock industry; first, an increased
number of installations, and second, longer periods of installations. The former can grow if moreinterlocks are installed among eligible offenders or if the definition of eligible offenders is
broadened. The latter can grow if installation times are longer, for example as a result ofcompliance-based removal. The first mechanism is measured by TIN (i.e., new installations in agiven year). The second mechanism is measured predominantly by TINall (i.e., all installations in agiven year, including those installed in a previous year). It is possible there are fewer new
installations in a year but TINall increased due to longer installation periods, or vice versa.

Incoming cases: Cases added to the court’s caseload during the reporting period andinclude New Filing, Reopened, and Reactivated cases.

!

Outgoing cases: Categories include Entry of Judgment, Reopened Dispositions, and Placedon Inactive Status.

Ultimately, three denominators were used to calculate installation rates: DWI arrests, DWI
convictions and incoming DWI cases. Outgoing cases were not considered appropriate to calculate
rates in the context of this study.
SurveyGizmo online software (www.surveygizmo.com) was used to capture the data in
combination with Microsoft Excel to calculate indicators and create tables and figures.

AIN is defined because of its face validity (meaning it is easy to understand given it reports “on thisday in this year, this number of devices were installed”). However, on its own it does not capturethat interlocks are not just installed but also removed, and serviced over a period of time, which
varies. Consequently, AIN may be more volatile from one year to the next; nevertheless, over time,
it is expected to reflect trends seen in TIN and TINall.

Installation rates
To place the interlock installation counts in context, and to measure installation rates, otherinformation about legislation and program features was gathered. Rates were calculated bycomparing the TIN with Driving while Intoxicated or Impaired (DWI) 4 arrest and conviction data.
Where available, data were examined for trends over time.
Installation rates were calculated by dividing the numerator TIN (number of new interlocks installed
in a calendar year) by different denominators and expressed as a percentage.
To calculate denominators, information about the total number of DWI arrests and convictions forthe year 2018 was gathered via state annual reports available online through state Highway Safety
Offices.
Data were also collected from the National Center for State Courts (NCSC) on both felony andmisdemeanor impaired driving cases for the past five years in 27 states. 5 For the purpose ofnational reporting, the NCSC requests states report a breakdown of their data by case types. Data
are provided by the state court administrator’s office and includes data from trial courts. The NCSC
uses the following definitions:!

!

Case: Generally initiated by a complaint. In two-tiered court systems, proceedings at thesecond step of a felony case are usually initiated by an information or indictment.

4

The abbreviation DWI (driving while intoxicated or impaired) is used throughout this report as a convenientdescriptive label, even though some states use other terms such as OUI (operating under the influence) or
DUI (driving under the influence), and in some states they refer to different levels of severity of the offense.
DWI is used not only to maintain consistency throughout the report but also because it is more descriptiveof the offense usually associated with drunk drivers.
5
Alaska, Alabama, Arkansas, Arizona, Colorado, Connecticut, Hawaii, Idaho, Iowa, Indiana, Kansas,
Kentucky, Louisiana, Massachusetts, Maryland, Maine, Missouri, Minnesota, Mississippi, North Carolina,
New Hampshire, New Mexico, Nevada, Pennsylvania, Rhode Island, Utah, Vermont, Washington, Wisconsin

5

6

RESULTS
As of March 1st, 2020, data were received from 25 states 6 and the District of Columbia. Somestates did not possess complete information needed to calculate each of the three indicators (TIN,
TINall, AIN) while a few others only provided information related to program features andarrest/conviction data. Of these states, 15 states7 also provided some or all of the data requested in2016.

Number of new, total and active installed interlocks
In terms of all interlocks installed in a vehicle at any time throughout the whole year, including
devices that may have been installed in previous years (TINall), the data revealed 223,223
installations within 17 states and Washington, D.C. When comparing total installations among the
12 states who provided TINall data for both 2016 and 2018 there was a 10% increase, from
143,471 in 2016 to 158,283 in 2018.
According to the TIN data provided by 18 states and Washington, D.C.,145,202 new ignitioninterlock devices were installed in 2018 (Table 1). When comparing new interlock installations
among the 12 states who provided TIN data for both 2016 and 2018 there was a 20% increase ininstallations, from 65,967 in 2016 to 79,013 in 2018.
An examination of the number of active installations (AIN) in a vehicle on December 31st revealed
141,480 devices installed at the end of 2018 within 16 states. When comparing active installations
among the 10 states who provided AIN data for both 2016 and 2018 there was a 5% decrease,from 110,159 in 2016 to 105,080 in 2018.
Table 1: State reported installation data
TINallState
Arkansas
California
Colorado
Connecticut
DelawareDistrict ofColumbia

2016
6,214
72,920
6,402
598

TIN

%
change30,008383%
201859,753
1,484
37

2016

-18% 24,718
677
148%
598

2018
5,375
27,207
17,493
10,063706%
change

-29%
1386%
18%

AIN December 31st
%
2016
2018
change
4,317
7,652
77%
57,894
6,950

48,867
7,935
834

582
223,223

Totals158,283

143,471

12,579

7,105
9,570
2,084
16,232
23,241

-34%
-29%
183%
62%

14,806

-4%

88
5,349
8,250
720

2,958
7,897

11,846

6,673
8,764
726
8,735
10,419

25%
6%
1%

6,795

-14%

11,67010,62010,145

52%

264
5,599

6,123

3,287
8,076

6,673

17%

618
8,512
14,769

-10%
-15%

7,927

-2%

6,672
8,169

12%

2,275
4
7,394

-7%

27
7,631
8,172

2791%
46%

1,300
8,590
3,938
391

1
5,695
51,205683
10,025

7,283
1,157

4,833
1,852
218%

19%

9,739

9,351

-4%

7,958

1,604

2,280

42%

4,256

6,527
8,121
-56%
552
359
-35%
1,278
1,333
4%
N/A 93,343 145,202
N/A 178,213 141,480
N/A
Totals based on states who reported in both 2016 and 2018
10% 65,967
79,013
20% 110,159 105,080-5%Six states provided data for 2014, 2015, 2016, and 2018 (Figure 3). These six states (Iowa,
Minnesota, New York, Pennsylvania, Virginia and Wyoming) were used to compare trends in TIN
and AIN (TINall has only been collected since 2016). Since 2014, in these six states there has been a
34% increase in TIN from 29,876 in 2014 to 40,085 in 2018. Further, AIN has increased 10% from36,469 in 2014 to 40,008 in 2018.

-16%
14%

22

6

Arkansas, California, Colorado, Connecticut, Delaware, Florida, Hawaii, Iowa, Kansas, Maine, Minnesota,
Missouri, New Jersey, New York, North Dakota, Oregon, Pennsylvania, Tennessee, Utah, Vermont, Virginia,
Washington, West Virginia, Wisconsin, Wyoming
7
Arkansas, Colorado, Connecticut, Delaware, Iowa, Kansas, Maine, Minnesota, New York, Oregon,Pennsylvania, Vermont, Virginia, West Virginia, Wyoming

7

18,514

FloridaHawaii
1,567
Iowa
10,805
Kansas13,516737
Maine
10,035
Minnesota
Missouri
6,193
Nebraska
15,397
New York
North
9,379
Carolina
Oregon6,680
Pennsylvania
South
1,394
Carolina
Tennessee
Utah
Vermont
123
Virginia
18,655West
5,132
Virginia
Wisconsin
15,274
1,314
Wyoming
Totals202,3358

were the outliers, where reported arrests were 70% and 40% lower, respectively, compared toincoming DWI cases.

Figure 3: Total new installs (TIN) and active installed (AIN) devices as reported by six
states in 2014-2016, 2018

In Arizona, a possible explanation may be the Administrative Office of the Courts reports
information by charge, not offense. For example, prosecutors may file five charges related to one
impaired driving offense. Therefore, one arrest could result with multiple charges.

45,00040,00035,000Regarding Pennsylvania, these data may be skewed by Philadelphia's two-tiered court system. Afteran arrest in Philadelphia, impaired driving cases are opened by a criminal complaint/affidavit.
Impaired driving defendants have the right to a full bench/judge-only trial in Municipal Court. Afterthe disposition, defendants can appeal to the Court of Common Pleas where they are given a trial
de novo (i.e., an entirely new trial). As a result, one arrest can lead to two different cases with two
different dispositions recorded. In sum, one impaired driving arrest in Philadelphia can result in two
court cases.

30,00025,00020,00015,00010,0005,000

Figure 5: State arrests and DWI case data, 2018

2014

2015
TIN

2016

2018

350,000

AIN: Dec. 31st
300,000

250,000

Impaired driving felony and misdemeanors
Data provided by NCSC revealed a steady increase in incoming DWI cases in 27 states from289,583 in 2014 to 493,454 in 2018 (Figure 4). This represents a 70% increase.

200,000

Figure 4: Incoming DWI cases, 2014-2018 (source: National Center for State Courts)

150,000

600,000

100,000

500,000

50,000400,000

AZ

300,000

CO

CT

ID

Arrests (State Data)

200,000

KY

MA

MO

Incoming DWI Cases

NC

PA

VT

WA

Total

Outgoing DWI Cases

Installation rate of interlocks among eligible population of offenders
An accurate way to measure the efficacy of an interlock program within a state is to estimate thepercentage of offenders who installed an interlock among those who were eligible or required to
do so.

100,000
2014

2015

2016

2017

2018

Dependent upon state legislation, the eligible population of offenders required to install aninterlock may be either those offenders arrested for DWI (if an administrative license suspension or
revocation requires an interlock) or those convicted of DWI. For the latter, this may be further

The 2018 NCSC data was consistent with state reported data, as is seen in Figure 5. Specifically,
incoming cases are similar to the number of arrests reported by the state. Arizona and Pennsylvania

910dependent upon categories of offenses requiring an interlock. Furthermore, some states may
include administrative per se cases. Some offenders may not be deemed eligible because of otherdriving or non-driving violations; for example, as a result of delinquent child support payments
unrelated to DWI.

When combining states with available data, the overall %TIN per DWI arrests was 48.41%, theoverall %TIN per DWI convictions was 56.73% and the overall %TIN per incoming DWI cases was
37.57%.
Table 2: 2018 percentage of interlocks installed (TIN) per DWI arrests, per DWI convictions
and per incoming DWI cases

The percentage of new interlocks installed per DWI arrests and convictions was calculated where
possible among states for which both the numerator and denominator were available. Figure 6
shows an increasing percentage of installations per DWI arrests and convictions since 2014.

2018
%
%TIN
%TIN per2018
Incoming convictions
State
per DWIDWI
Convictions
DWI
per DWI
arrests convictions
Cases
arrests
9,569
7,696
80.43%
56.17%
69.84%
Arkansas
123,253
22.07%
California
21,244
19,476
21,54491.68%
82.34%
89.82%
Colorado
Connecticut
4,156
2,595
7,832
62.44% 242.13%
387.78%Delaware
1,852
38.12%
Florida32,17739.09%
12,702
Iowa
7,271
10,079120.53%Kansas23,024
18,56780.64%
Kentucky
5,811
5,394
12.49%
Maine
27,974
Minnesota
18,962
8,007
14,11842.23%
54.95%
130.12%
Missouri
18,11637.51%New York
49,73025,677
83,52251.63%
16.43%
31.83%
Pennsylvania
10,042
7,798
77.65%
18.44%
23.75%
Utah
Virginia
21,30819,79092.88%
43.88%
47.25%
Wyoming
1,556
23.07%
Totals319,276
138,401
183,165
N/A
N/A
N/A
Totals and installation rates based on states without missing data1
Totals158,035
109,606
69.36%
48.41%
56.73%
2018
Arrests

Figure 6: New interlock installations per DWI arrests and per convictions as a percentage
in 2014-2016, 2018
60.0%

56.7%

50.0%

46.9%

48.4%

41.7%
40.0%
35.3%
31.8%
30.0%
20.6%
20.0%

17.5%

10.0%

0.0%
2014

2015

% new installations per DWI arrest

2016

2018

% new installations per DWI conviction

Table 2 presents 2018 percentages of new interlocks installed (TIN) per DWI arrests, per DWI
convictions and per incoming DWI cases.

1

For context, Connecticut, Kansas, and Missouri (where numbers were above 100%) required aninterlock for all offenders, including administrative per se cases (failure or refusal of chemical test atarrest). These results over 100% are an overestimate because the correct denominator to accurately
calculate the rate was not available (when calculating the national rates, a correction was used forthese states).
Ideally there would be a 100% installation rate. However, as presented below (Table 2), theinstallation rate ranges from 9.78% (%TIN per incoming DWI cases in Pennsylvania) to 89.82%(%TIN per DWI convictions in Colorado).

11

12%TIN perincoming
DWI cases

81.20%
128.49%52.54%
86.95%
13.46%
31.23%
73.80%
9.78%

N/A
37.57%

Calculation of total %TIN per DWI arrests, %TIN per DWI convictions and %TIN per incoming DWI cases capped the
TIN value at the number of DWI arrests, convictions and incoming cases in case TIN values were higher than arrests,
convictions or incoming cases (effectively reducing the % for Connecticut, Kansas and Missouri to 100%).

done so. This is demonstrated through the arrest and conviction data which shows the 2018 TIN
per 2018 DWI arrests was 48.41%, per 2018 DWI convictions was 56.73% and per 2018 incoming
DWI cases was 37.57%. While the indicators for DWI arrests and convictions have consistently
increased over time (the corresponding percentages were 17.5% and 35.3% in 2014; no historical
data were available for incoming DWI cases) ultimately, they are not nearly close to 100%.

CONCLUSIONS
Alcohol ignition interlock programs are essential to decrease the number of alcohol-impaired
drivers, crashes, and fatalities. Their value as an alcohol-impaired driving countermeasure is evident
in light of the strong body of evidence showing they not only reduce recidivism but can lead to a
reduction in alcohol-related fatalities when the use of the device is embedded in strong legislation.
But to be efficacious, market penetration is crucial, and all offenders required to install a device
must actually install a device. As such, the purpose of this annual data collection is to monitor
installations and installation rates, and to report these findings to help strengthen interlock
programs.

In conclusion, the preponderance of the evidence shows considerable growth in the industry yet
confirms a relatively low installation rate among all eligible offenders.

The state data shows significant growth in the use of interlocks:!

There was a 20% increase in TIN according to data from 12 states (from 65,967 interlocks
in 2016 to 79,013 interlocks in 2018);!

There was a 10% increase in TINall according to data from 12 states (from 143,471
interlocks in 2016 to 158,283 interlocks in 2018).

!

Among six states that provided TIN data from 2014 to 2018, there was a 34% increase(from 29,876 interlocks in 2014 to 40,085 interlocks in 2018).

TINall in this report is based on data collected from a limited number of states. As such, if datafrom all jurisdictions installing interlocks were available, then TINall would be considerably higher.
Assuming the 10% growth rate between 2016 and 2018 in these 12 states is representative ofgrowth nationally, it is estimated national installations would increase from 614,626 in 2016
(Robertson et al., 2018) to 676,089 in 2018.
While both TIN and TINall show considerable growth, AIN suggests the opposite with a decrease of
5% between 2016 and 2018. However, caution is warranted given that AIN is more volatile. Since
AIN is a snapshot of one day (the number of installed devices on December 31st), it is subject to all
the dynamics/market forces/mechanisms that can cause volatility. Conversely, indicators examining
a year of data, notably TIN and TINall, are expected to be more stable because they represent a
longer period of time. While year-to-year volatility is possible, over time, AIN is expected to follow
trends in TIN and TINall. This is confirmed when comparing AIN results over a longer period of time,
revealing a 10% increase between 2014 and 2018.
One hypothetical example of a market force causing this sudden drop in AIN of 5% is the decertification of one device or vendor resulting in a large number of removals. This could cause atemporary decrease in the number of actively installed devices that would bias the overall count if
installations were counted on a day after deinstallation with one vendor and before reinstallation
with another. Other mechanisms could play a similar role; their compounded impact on AIN may beeven more pronounced because of year-over-year changes in holiday service hours on December
31st.
Regardless of the observed increases in TIN, TINall and AIN since 2014, there remains a large
contingent of eligible offenders on the road who are required to install an interlock but have not

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Willis C., Lybrand S., and Bellamy N. (2004). Alcohol ignition interlock programmes for reducing
drink driving recidivism. Cochrane Database Syst Rev.; (4): CD004168. DOI:
10.1002/14651858.CD004168.pub2.

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