Traffic searches by highway patrols in Washington and Colorado have dropped by nearly half since the states voted to legalize cannabis in 2012, according to a story by NBC News which used data from the Stanford Open Policing Project.

Racial disparities in searches also decreased, but Blacks and Hispanics are still more likely to get searched than their white counterparts.

Cannabis legalization eliminated one of the major justifications used by police officers to stop motorists. In Colorado, searches dropped initially by 30 percent then flattened out to more than a 50-percent drop within one year. In Washington, searches dropped by 50 percent within three months of cannabis legalization and remained at low rates thereafter. Twelve states the study analyzed that did not pass any sort of decriminalization legislation did not experience significant drops in search rates.

The Stanford Open Policing Project, composed of a team of researchers and statisticians, collected more than 60 million records of traffic stops and searches by highway patrol officers in 22 states. By analyzing this data, the group hopes to promote a deeper understanding of the most common interaction Americans have with police.