Endogenous Driving Behavior in Tests of Racial Profiling in Police Traffic Stops

African-American motorists may adjust their driving in response to increased scrutiny by law enforcement. We develop a model of police stop and motorist driving behavior and demonstrate that this behavior biases conventional tests of discrimination. We empirically document that minority motorists are the only group less likely to have fatal motor vehicle accidents in daylight when race is more easily observed by police, especially within states with high rates of police shootings of African-Americans. Using data from Massachusetts and Tennessee, we also find that African-Americans are the only group of stopped motorists whose speed relative to the speed limit slows in daylight. Consistent with the model prediction, these shifts in the speed distribution are concentrated at higher percentiles of the distribution. A calibration of our model indicates substantial bias in conventional tests of discrimination that rely on changes in the odds that a stopped motorist is a minority.