LogFAQs > #893078102

http://aircarecolorado.com/index.php/consumer-information/collector-plates

Apparently these are the restrictions for Colorado. I swear that not all of them have those plates though. Based on the second bullet point, I think that most of them must be grandfathered in and not have to re-test. I didn't know there was a mileage restriction, but I was thinking that's a good idea. Though 4,500 sounds kind of like a lot to me; if you don't have a long work commute you could still use that as your "regular" vehicle. I average about 6,000 a year