Analysis: No systematic agency bias in Washington State Patrol traffic stops

A Washington State Patrol car driving next to a lake on a mountain road.
Researchers with WSU’s Division of Governmental Studies and Services analyzed data on more than 7 million Washington State Patrol contacts to help the agency better understand interaction with the public (WSP photo).

Researchers at Washington State University found no evidence for intentional, agency-level racial bias in an analysis of five years of traffic stops conducted by the Washington State Patrol.

Racial profiling and biased policing have received increased attention nationwide. Contracted by the Washington State Patrol (WSP) in 2020 to examine traffic stop records for evidence of bias, researchers with WSU’s Division of Governmental Studies and Services (DGSS), supported by faculty from the Department of Criminal Justice and Criminology, analyzed data on more than 7 million trooper contacts, including more than 3.4 million traffic stops, 47,000 calls for service, and 175,000 collisions, occurring from Jan. 1, 2015, to Dec. 31, 2019.  

The 10-person WSU research team compared trooper contacts with census data, the statewide driving population, and other measures. Researchers found no evidence of systematic racial profiling. 

“This research connects the expertise of Washington’s land-grant university to a pressing public issue,” said DGSS Director Christina Sanders. “Our results help inform policy and public dialogue for the better, offering opportunities for improved in-person interactions with the people of our state, fine-tuning of trooper management and training, and better service to Washington overall.

“Washington State Patrol leaders should take pride in the fact that they are genuinely interested in knowing exactly what the data show and are not backing down on their commitment to further investigate and make changes for improvement,” she added. 

The team’s Traffic Stop Data Report is accessible online at

Traffic stop analysis

Examining traffic stop data, WSU scientists found that no groups were significantly overrepresented in both officer contacts and calls for service.

White motorists were stopped at nearly the same rate statewide as their proportion of the population. Compared to their statewide population, Black motorists are stopped slightly more often. Native American, Asian, Pacific Islander, and Hispanic drivers were stopped at lower rates compared to population. 

Researchers also compared stops made during the day to those made at night, under the assumption that if racial profiling is occurring, there would be more stops of people of color during daylight, when it is easier to see the race of a driver.  Differences between day and night stops were minimal, and for many groups the stop percentages were equal.

Several counties showed disproportionate stops compared to census data: Benton County for Hispanic drivers, King and Pierce Counties for Black drivers. White drivers were stopped more than they were assisted by the WSP in 10 counties, while Hispanic motorists were stopped more than they are assisted in Franklin County.

Examining data from more than 120,000 searches, scientists found that Native American, Hispanic, and Black drivers are more likely to be searched than White drivers.  White motorists received the most citations, but their overall proportion of total citations fell over the five-year period. Asian/Pacific Islander and Hispanic drivers are more likely to receive a citation compared to White drivers, but Native American and Black drivers are statistically less likely to receive a citation.

DGSS will work with WSP to study and better understand areas of apparent, unexplained disparities for Black and Hispanic drivers. Researchers plan to conduct in-person focus groups with community members to learn about their experiences and relationship with officers. Scientists also suggested ways to improve data collection for future studies.

“We appreciate and respect the findings from WSU’s Division of Governmental Studies and Services,” said WSP Chief John R. Batiste. “They are recognized nationally and internationally as impartial and thorough academic professionals, and their findings are both trusted and instructive. I am heartened to see that once again, after thorough study, no evidence of systemic or intentional bias can be found in our traffic enforcement operations. 

“However, we will continue to constantly monitor our operations and use trusted outside reviewers and advisors to continuously improve,” Batiste added. “In our business, there is simply no room for failure when it comes to fairness.”  

The research team included Sanders; Season Hoard, associate professor and project manager with DGSS; David Makin and Dale Willits, associate professors with the Department of Criminal Justice and Criminology; Brian Anderson, research coordinator with DGSS; and a team of five student researchers: Megan Bartol, Kaitlynn Boardman, Angelo Brown, Abbas Mammadov, Megan Parks, and Helery Yakub. Michael Gaffney, director of WSU Extension’s Community and Economic Development Program Unit and former director of DGSS, advised the team’s work. The study was funded by the Washington State Legislature and WSP.

The latest research follows prior WSU studies on WSP practices over four decades that have built university capacity and experience in law-enforcement review. Independent WSU reviews have included statewide surveys and traffic stop analyses, including a study of two million WSP contacts between May 2000 and October 2002.

NOTE: This was updated Dec. 3, 2021 to better reflect one of the study’s findings involving slight over-representation of Black motorists in traffic stops by WSP compared to statewide population.

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