The association of Public Safety Power Shutoffs and motor vehicle crashes

Utility companies in California de-energize equipment during periods of high wildfire risk. These Public Safety Power Shutoffs (PSPS) are designed to prevent power lines from igniting wildfires. The loss of electricity and subsequent failure of traffic signals may increase the risk of motor-vehicle crashes.

We determined the daily number of motor-vehicle crashes per county for all 58 California counties between September 15th and November 30th, 2019, a period of high wildfire risk. We obtained electrical circuit-level information from the California Public Utilities Commission and created two daily PSPS exposure metrics: the equivalent to (1) the number of utility customers and (2) the percent of households in the county without power for a full day. Exposure metrics were categorized into quartiles of households or population impacted by PSPS. We generated random effects negative binomial models to estimate the association between PSPS exposure quartile and motor-vehicle crashes at the county-day level.

We observed 522 county-days that experienced a PSPS event and 104,627 motor-vehicle crashes during our 77-day study period. Effect estimates from models using the two exposure metrics were similar. Higher levels of PSPS exposure were associated with slight decreases in the rate of motor-vehicle crashes. In the customer-day model, the highest level of PSPS exposure was associated with a 7% decrease in motor-vehicle crashes per 100,000 county residents (RR: 0.93, 95% CI: 0.88-0.98) compared to days without PSPS.

Despite the failure of traffic signals, road lighting, and other traffic safety equipment during power outages, the fall 2019 PSPS events were not associated with an increase in motor-vehicle crashes, potentially due to changes in driving habits and behavior.

PSPS may have unintentional consequences. Motor-vehicle safety during PSPS should be a focus of future monitoring efforts.