Most states have titling and registration laws that require residents to title and register their cars in the state—and for new residents of the state to do so within some period of time, such as 30 days. Some states require titled cars to pass a comprehensive safety inspection. And some states also require cars owned by residents of certain counties to pass an emissions test/inspection designed to improve air quality in more densely populated counties.
In Washington State, residents are required to title and register their vehicles with the Washington State Department of Licensing (DOL). New residents must title and register their vehicles within 30 days of becoming a resident. The state does not require a comprehensive safety inspection for vehicles to be titled or registered. However, Washington does require emissions testing for vehicles in certain counties. The emissions testing program is designed to improve air quality in densely populated areas. As of January 1, 2020, the emissions testing program ended, but vehicles registered in Clark, King, Pierce, Snohomish, and Spokane counties previously required emissions tests. It's important for residents to check the current requirements, as regulations can change and may vary based on the age and type of vehicle.