Is the DUI offender’s BAC at the time of arrest related to the effectiveness of interlocks?

Alcohol vehicle interlocks have proved to be very effective in reducing the recidivism of motorists convicted of driving under the influence (DUI) offenses. In the United States the use of interlocks is tended to be restricted by the states to multiple offenders and first offenders with high BACs (generally >0.15); based in part on the argument that interlocks would be ineffective with low BAC first offenders. The purpose of this paper is to determine the relationship between BAC and the effectiveness of the interlock in reducing recidivism. The state of New Mexico has a comprehensive interlock program requiring all DUI offenders to install interlocks, or remain suspended indefinitely. We compared the relative recidivism of suspended drivers with those offenders on interlocks as a function of five BAC categories: 0.08-0.11; 0.12-0.15; 0.16-0.19; 0.20-0.23; and 0.24-0.43. Interlocked offenders had 60% to 80% lower recidivism rates which did not vary as a function of arrest BAC or number of prior offenses. The effectiveness of the interlock in reducing recidivism relative to license suspension is essentially the same for DUI offenders at low BACs as it was for those with high BACs. Current state laws which do not extend the interlock requirement to low BAC first offenders should be reconsidered.