The Geography of Sobriety Checkpoints and Alcohol-Impaired Driving.

BACKGROUND AND AIMS Sobriety checkpoints are an effective strategy to reduce alcohol-impaired driving, motor vehicle crashes, injuries, and fatalities. The aim of this study was to identify the geographic extent over which individual sobriety checkpoints affect alcohol-impaired driving. DESIGN, SETTING, PARTICIPANTS Spatial ecological panel analysis using geolocated breath test data from the Queensland Police Service, Australia, for January 2012 to June 2018. Data were aggregated over 338 weeks within 528 Statistical Area level 2 (SA2) units (n=178,464 SA2-weeks) and 84 Statistical Area level 3 (SA3) units (n=28,392 SA3-weeks). SA2 units in Queensland contain a mean population of 8,883.5 (standard deviation (SD)=5,5018,3) and encompass 468.9 roadway kilometers (SD=1,490.0); SA3 units contain a mean population of 57,201.6 (SD=29,521.6) and encompass 2,936.0 roadway kilometers (SD=7,025.0). MEASUREMENTS Independent measures were the density of sobriety checkpoints conducted per 500 roadway kilometers within local and spatially adjacent space-time units. The dependent measure was the rate of tests that detected breath alcohol concentration (a proxy for Blood Alcohol Concentration [BAC]) greater than the legal maximum value of 0.05% for fully licensed drivers in Queensland. Bayesian hierarchical spatial negative binomial models related sobriety checkpoints to the rate of breath tests with BAC≥0.05% within and between space-time units. FINDINGS One additional sobriety checkpoint conducted per 500 roadway kilometers was associated with 2.5% reduction in the rate of breath tests with BAC≥0.05% within local SA2 units (incidence rate ratio (IRR)=0.975; 95% credibility interval (CrI): 0.973, 0.978), and with 5.5% reduction in the rate of breath tests with BAC≥0.05% within local SA3 units (IRR=0.945; 95%CrI: 0.937, 0.953). Associations were attenuated towards null in spatially adjacent units and in temporally lagged units (e.g., SA3-weeks; adjacent lagged 1 week: IRR=0.969; 95%CrI: 0.937, 1.003). CONCLUSIONS Individual sobriety checkpoints appear to be associated with reductions in nearby alcohol-impaired driving. Relationships decay after approximately 1 week and beyond local areas containing approximately 60,000 residents and 3,000 kilometers of roadway.