This Article empirically illustrates that legal doctrines permitting police officers to engage in pretextual traffic stops may contribute to an increase in racial profiling. In 1996, the U.S. Supreme Court held in Whren v. United States that pretextual traffic stops do not violate the Fourth Amendment. As long as police officers identify an objective violation of a traffic law, they may lawfully stop a motorist—even if their actual intention is to use the stop to investigate a hunch that by itself does not amount to probable cause or reasonable suspicion.

Scholars and civil rights activists have sharply criticized Whren, arguing that it gives police officers permission to engage in racial profiling. But social scientists have struggled to empirically evaluate how Whren has influenced police behavior.

A series of court decisions in the State of Washington presents an opportunity to test the effects of pretextual-stop doctrines on police behavior. In the years since the Whren decision, Washington has experimented with multiple rules that provide differing levels of protection against pretextual stops. In 1999, the Washington Supreme Court held in State v. Ladson that the state constitution barred police from conducting pretextual traffic stops. However, in 2012, the court eased this restriction on pretextual stops in State v. Arreola.

Exploiting a dataset of 8,257,527 traffic stops conducted by the Washington State Patrol from 2008 through 2015, we carry out difference-in-differences and triple-difference analyses to assess whether the Arreola decision increased traffic stops among drivers of color relative to white drivers. We find that the Arreola decision is associated with a statistically significant increase in traffic stops of drivers of color relative to white drivers. Further, we find this increase in traffic stops of drivers of color is concentrated during daytime hours, when officers can more easily ascertain a driver’s race through visual observation.