If you keep track of our sister site AutoHunter, you may have seen several Kei vehicles listed in the past. Depending on your inclinations (JDM or otherwise), if you’re interested in buying one, it may serve you well to research your home state’s laws because it’s quite possible that you cannot register it there. For Colorado residents, that’s about to change.
While the pronunciation may sound like an Iacocca-era Mopar, Kei vehicles are the smallest class of vehicle available to license on Japanese roads. Kei is short for kei-jidosha, which translates to “light vehicle,” a creation of Japanese regulations. Owners in Japan pay lower tax and insurance rates as the regulation limits engine size (under 660cc), length (11.2 feet), width (4.9 feet), and height (6.6 feet). It seems that horsepower tends to be limited to 63 horsepower and under, but not officially.
According to Car and Driver, Colorado enthusiasts had been buying Kei vehicles, only to discover that once the temporary registration had expired, they could not register their nifty, new collectible. The latter was dependent on the county, as certain ones required emissions testing; those that did not require the testing created no problems with registration.
Colorado Governor Jared Polis somewhat settled the issue, signing into law HB25-1281 (you can read it here). It officially recognizes Kei vehicles as legal on state roads and gives them legitimacy for titling, registration, and use in the state, though the new law says Kei vehicles can’t be driven on roads that have a speed limit over 55 mph. Emissions will also be handled differently—while dynamometers are used for conventional vehicles, a static two-speed idle test will be used for Keis, which is the same method used for vehicles built in 1981 and earlier. However, the law does not go into effect until July 1, 2027.

Says Governor Polis. “We’re excited in Colorado that now Coloradoans have another vehicle choice to get where they want to go. And I would encourage other states to take the same step.”
Currently, 29 states allow for Kei vehicles (of course, 25 years or older) on public roads. Each state oversees it differently, including one that restricts speed to 35 mph or less within a 25-mile radius of the owner’s residence (hello, New Hampshire, what’s up with that?). If you live in Connecticut, Georgia, Iowa, Maryland, Nevada, New Jersey, New Mexico, Oregon, or Vermont, you cannot even register a Kei vehicle. The lesson learned here is: Do your research before pulling the trigger.