Evaluation of Maryland's State Police Impaired Driving Reduction Effort (SPIDRE)

To help address the dangers of impaired driving on its roadways, Maryland highway-safety and law-enforcement officials collaborated closely in 2012 on the idea of building a new program that brought together a dedicated police unit (utilizing the model of high visibility enforcement) and a data-driven approach for the unit's deployment. After extensive research by the Maryland Department of Transportation Highway Safety Office (MHSO) and the Maryland State Police, and a one-time infusion of federal transfer funds, the State Police Impaired Driving Reduction Effort (SPIDRE) was initiated in 2013. With funding from the Maryland Highway Safety Office, the University of Maryland subcontracted with NORC to determine the impact of the SPIDRE program on DUI arrests, impaired driving crashes and public perceptions of DUI enforcement.

A ratio of single vehicle nighttime (SVN) (6PM-6AM) crashes to multiple vehicle daytime (MVD) (6AM-6PM) was used as a measure of impaired driving crashes (serving as a surrogate measure of impaired driving crashes to account for underreporting of impaired drivers by police in official crash reports). There was a statistically significant decrease of 0.009 in the ratio of single vehicle nighttime to multiple vehicle daytime crashes in the SPIDRE counties, but not in any other counties. This implies that there was an effect by the SPIDRE program in this measure. The decrease in the ratio translates to 178 SVN crashes avoided in the SPIDRE counties over the 35 month SPIDRE implementation period. Using a similar methodology, if the SPIDRE team had operated in the non-SPIDRE counties and had the same effect on the ratio measure, 192 SVN crashes would have been avoided. The benefit/cost ratio for the SPIDRE program was a savings of $3.75 for every $1.00 spent on the program. Recommendations included implementing SPIDRE teams for 9-12 months in targeted counties instead of 1-3 months.

Bar Patron Surveys. Pre-test and post-test bar patron surveys were conducted and used to collect data from people who were exiting various bars in Montgomery County (SPIDRE) and Cecil/Harford counties (Non-SPIDRE). These popular bar patrons were identified as most likely to be drinking and driving and therefore potentially influenced by the SPIDRE enforcement efforts. Approximately 100 patrons were surveyed and breath tested for alcohol outside selected bars in each jurisdiction before the SPIDRE program began and 6 months later after the program had been operating in the SPIDRE county.

Evidence from this evaluation indicated that the SPIDRE team was associated with preventing a downward trend in DUI arrests in SPIDRE counties. Further, the SPIDRE program was associated with a 12% increase in the rate of positive adjudicative outcomes from DUI arrests. In addition to the reduction in DUI crashes, these findings suggest additional benefits of the SPIDRE team and indicate that the level of improvement in enforcement and adjudicative outcomes approaches the projected 10% estimate for improvement in DUI arrests.