• Effectiveness of an ignition interlock device in reducing alcohol-impaired driving recidivism and alcohol-impaired motor vehicle crashes in Maryland

      Kerns, Timothy; Smith, Gordon S., M.B., Ch.B., M.P.H.; Hirshon, Jon Mark (2017)
      Background: Multiple studies have shown that ignition interlock devices reduce alcohol impaired driving recidivism while the device is installed on the vehicle. However, many of these studies rely on convictions and have limited follow-up after the device has been removed from the vehicle. Objectives: The aims of this study were to compare the characteristics of drivers who installed an ignition interlock device after receiving an alcohol impaired driving citation and a control group that did not install the device and to determine their risk of receiving a subsequent alcohol related citation or being involved in an alcohol related crash. Methods: A Cox proportional hazard test was used to compare the risk of a subsequent citation or motor vehicle crash between the study groups. Results: The interlock group had a lower proportion of females (22.2% interlock vs 24.2% control, p<0.05), and a higher mean age (36.5 years vs 34.3 years, p<0.05). Forty-six percent of those installing an ignition interlock device had a BAC above 0.15 g/dL as compared with 25% in the control group (p<0.05). The BAC test refusal rate was higher among interlock installers (41.4% vs 33.0%, p<0.05). While the device was installed on the subject's vehicle, drivers were 22% less likely to receive an impaired driving citation as compared to the time when the device was not installed (HR=0.78; 95% CI: 0.73-0.84). After removal, the interlock group was 32% more likely to receive an impaired driving citation versus controls (HR=1.32; 95% CI: 1.22-1.42). Similar patterns were observed with respect to motor vehicle crashes. Conclusion: Drivers who have installed an ignition device on their vehicle have a lower risk of receiving a subsequent alcohol involved driving citation and of being involved in an alcohol related motor vehicle crash while the device is on the vehicle as compared to the control group. Upon removal, the risk of both citations and crashes is higher for those who had an interlock device installed. Ignition interlock devices are effective for the time they are used but should not be the only tool to prevent future events of alcohol involved driving among those previously arrested for impaired driving.