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 Colorado, residents are required to title and register their vehicles with the Colorado Department of Revenue through the Division of Motor Vehicles (DMV). New residents must title and register their vehicles within 90 days of establishing residency. Colorado does not mandate a state-wide vehicle safety inspection, but it does require emissions testing for vehicles in certain counties. These counties, typically the more densely populated ones, include the Denver-Boulder area, parts of Larimer, Weld, El Paso, and several others. The emissions program aims to improve air quality and is required for most gasoline and diesel vehicles. The frequency of the emissions test varies depending on the age of the vehicle, but it is generally required every two years for most vehicles. Exemptions are available for certain types of vehicles, including electric cars, motorcycles, and vehicles that are seven model years old or newer.