Alcohol Ignition Interlocks

Alcohol ignition interlocks are devices installed in vehicles that measure alcohol on the driver’s breath. They are also called ignition interlocks or alcohol interlocks. An alcohol interlock keeps a vehicle from starting if the driver has a blood alcohol concentration above a certain level, usually 0.02%.1 They are used for driving while impaired (DWI) offenders and can be used to monitor drinking and driving behavior while the offender is on probation.1 Interlocks that require retests while drivers are operating vehicles (running retests) help to ensure that drivers remain sober while driving.1 One of the interventions in MV PICCS is for alcohol interlocks to be installed on the vehicles of all DWI offenders, including first-time offenders.

Effectiveness and Use of Interlock Devices

Alcohol interlocks are highly effective in allowing sober drivers to start a vehicle and preventing alcohol-impaired drivers from doing the same.1 Use of interlocks is substantially higher in jurisdictions that require interlocks for license reinstatement or offer them as an alternative to home confinement.1

A Community Guide Systematic Review of studies through 2007 found strong evidence that alcohol interlocks are effective in reducing recidivism (continued alcohol-impaired driving, as measured by re-arrest) for alcohol-impaired driving while they are installed in offenders’ vehicles.2,3 Consistent with this prior research, a recent evaluation of legislation changes in Washington state found that, as the alcohol interlock laws were strengthened, more first-time offenders had interlocks installed and fewer were re-arrested during the two years after initial arrest.4

However, the Community Guide Systematic Review also found that reductions in re-arrest rates largely go away once alcohol interlocks are removed.2,3 A 2016 study evaluated a Florida policy addressing this problem.5 The policy required DWI offenders with alcohol interlocks to undergo alcohol use disorder (AUD) treatment if they committed at least three violations while the interlock was installed on their vehicle.5 Violations were defined as two attempts to start the vehicle with a BAC over 0.05% during a four-hour period. The group that received AUD treatment while they had interlocks installed on their vehicles were less likely to be re-arrested during the four years following interlock removal compared to the group that had interlocks but did not receive AUD treatment.5

The Community Guide Systematic Review also found that studies examining the effects of installed alcohol interlocks on alcohol-related crashes are limited but suggest that alcohol-related crashes decrease while interlocks are installed.2,3 Recent research has provided evidence that ignition interlock laws can prevent alcohol-impaired or alcohol-involved traffic deaths.6 A 2016 study compared U.S. states that introduced laws requiring alcohol interlocks for all DWI offenders to U.S. states without these laws.7 The authors found that the states with these laws experienced fewer alcohol-involved crash deaths (defined as crashes where at least one driver had a BAC higher than 0%) than the states without these laws.7 A 2017 study assessed the effects of state alcohol interlock laws on crashes involving alcohol-impaired drivers (BAC 0.08% or higher).8 The authors found that laws requiring alcohol interlocks for all DWI offenders (including first-time offenders) were associated with decreases in the rates of fatal crashes where at least one driver had a BAC of 0.08% or higher and fatal crashes where at least one driver had a BAC of 0.15% or higher.8

Recent or Current Legislation by State

You can visit the alcohol interlock laws by state webpageexternal icon on the Insurance Institute for Highway Safety’s website for up-to-date information on alcohol interlock policies, requirements, and laws by state.9,10 The Governors Highway Safety Association also maintains information about alcohol-impaired driving laws by state on their state laws – alcohol impaired driving webpageexternal icon.11

Costs of Interlock Programs and Time to Implement

Offenders are usually required to pay the costs associated with alcohol interlocks in their vehicles. These costs includes an installation fee, monthly usage fee, recalibration fees, and a removal fee.1 Some states (such as Illinois and New Mexico) have funding available for offenders with lower incomes to help reduce these costs.1

The implementation of alcohol interlock programs often requires legislation.1 Once legislation is passed, it typically takes four to six months for implementation, including the establishment of a network of interlock equipment providers.1

Other Issues and Resources

You can read Chapter 1, Section 4.2 of NHTSA’s Countermeasures that Work: A Highway Safety Countermeasure Guide for State Highway Safety Officespdf iconexternal icon (Tenth Edition, 2020) to learn more about the topics above and other issues related to alcohol interlocks, such as barriers to use and public support of alcohol interlocks and implementation information.1

Detailed information about the history of alcohol interlock legislation by state can be found in the 2017 article U.S. State Ignition Interlock Laws for Alcohol Impaired Driving Prevention: A 50 State Survey and Analysisexternal icon.12

More information can also be found on The Community Guide’s webpage covering Motor Vehicle Injury – Alcohol-Impaired Driving: Ignition Interlocksexternal icon.13

You can read the RAND Corporation’s final reports for MV PICCS 1.0/2.0external icon and MV PICCS 3.0external icon for more information about how effectiveness and costs were incorporated into the MV PICCS tool for this intervention.


The first interlock was developed in 1969.14 Interlocks with alcohol-sensing devices (instead of performance-based devices) became the standard in the 1980s.14 In the 1990s, alcohol interlocks with additional features that prevented overcoming the interlock, such running retests, were developed.15 In 1992, NHTSA issued the first certification guidelines for alcohol interlock devices, which gave advice to states on evaluating interlock hardware that was on the marketplace and available for installation.14,15

In the early 1980s, states began enacting administrative license revocation (ALR) laws, which allow police officers to seize a driver’s license for impaired driving at the time of arrest. The license would then be suspended by the state motor vehicle department for a set period.16 While ALR laws allow for a swift penalty to be applied, they are difficult to enforce because the offender’s license status is only checked when the driver’s vehicle is stopped for another traffic violation.16 Laws directed at vehicles, such as license plate impoundment, vehicle impoundment, and vehicle forfeiture, avoid this problem.16 In 1986, California passed legislation allowing for pilot tests of alcohol interlocks in several California counties; other states soon after introduced interlock legislation.14 Federal legislation in 1998 and 2012 provided financial incentives to states that passed their own interlock legislation.6 As of 2021, all states have alcohol interlock programs, but there is variation among the states in whether the interlocks are mandatory and for which offenders they are implemented.11 See above for current legislation.


  1. Venkatraman, V., Richard, C. M., Magee, K., & Johnson, K. (2021). Countermeasures that work: A highway safety countermeasures guide for State Highway Safety Offices. (Report No. DOT HS 813 097). Washington, DC: National Highway Traffic Safety Administration iconexternal icon
  2. Elder, R. W., Voas, R., Beirness, D., Shults, R. A., Sleet, D. A., Nichols, J. L., . . . Task Force on Community Preventive Services. (2011). Effectiveness of ignition interlocks for preventing alcohol-impaired driving and alcohol-related crashes: A community guide systematic review. American Journal of Preventive Medicine, 40(3), 362–376. icon
  3. Task Force on Community Preventive Services. (2011). Recommendations on the effectiveness of ignition interlocks for preventing alcohol-impaired driving and alcohol-related crashes. American Journal of Preventive Medicine, 40(3), 377. icon
  4. McCartt, A. T., Leaf, W. A., & Farmer, C. M. (2018). Effects of Washington state’s alcohol ignition interlock laws on DUI recidivism: An update. Traffic Injury Prevention, 19(7), 665–674. icon
  5. Voas, R. B., Tippetts, A. S., Bergen, G., Grosz, M., & Marques, P. (2016). Mandating treatment based on interlock performance: Evidence for effectiveness. Alcoholism: Clinical & Experimental Research, 40(9), 1953–1960. icon
  6. National Academies of Sciences, Engineering, and Medicine. (2018). Getting to zero alcohol-impaired driving fatalities: A comprehensive approach to a persistent problem. Washington, DC: The National Academies Press. icon
  7. Kaufman, E. J., & Wiebe, D. J. (2016). Impact of state ignition interlock laws on alcohol-involved crash deaths in the United States. American Journal of Public Health, 106(5), 865–871. icon
  8. McGinty, E. E., Tung, G., Shulman-Laniel, J., Hardy, R., Rutkow, L., Frattaroli, S., & Vernick, J. S. (2017). Ignition interlock laws: Effects on fatal motor vehicle crashes, 1982–2013. American Journal of Preventive Medicine, 52(4), 417–423. icon
  9. Insurance Institute for Highway Safety, & Highway Loss Data Institute. (2021). Alcohol and drugs. icon. Accessed on 1/27/2022.
  10. Insurance Institute for Highway Safety, & Highway Loss Data Institute. (2022). Alcohol interlock laws by state. icon. Accessed on 1/27/2022.
  11. Governors Highway Safety Association. (2021). State laws by issue: Alcohol impaired driving. icon. Accessed on 1/27/2022.
  12. Shulman-Laniel, J., Vernick, J. S., McGinty, B., Frattaroli, S., & Rutkow, L. (2017). U.S. State ignition interlock laws for alcohol impaired driving prevention: A 50 state survey and analysis. The Journal of Law, Medicine & Ethics, 45(2), 221–230. icon
  13. Guide to Community Preventive Services. (2021). Motor vehicle injury – alcohol-impaired driving: Ignition interlocks. icon. Accessed on 1/27/2022.
  14. Marques, P. R., & Voas, R. B. (2010). Key features for ignition interlock programs (Report No. DOT HS 811 262). Washington, DC: National Highway Traffic Safety Administration iconexternal icon
  15. Marques, P. R., Voas, R. B., Roth, R., & Tippetts, A. S. (2010). Evaluation of the New Mexico ignition interlock program. (DOT HS 811 410). Washington, DC: National Highway Traffic Safety Administration iconexternal icon
  16. Voas, R. B., & Deyoung, D. J. (2002). Vehicle action: Effective policy for controlling drunk and other high-risk drivers? Accident Analysis & Prevention, 34(3), 263–270. icon