IIHS makes state law table and interactive map describing medium-speed vehicles available online
In September 2008, NHTSA denied a petition for rulemaking to create a new class of motor vehicles known as medium speed vehicles (MSV). The petitioners proposed that MSVs have a top speed of 35 mph and that they be held to less stringent safety standards than passenger cars. NHTSA, taking environmental and fuel consumption issues into consideration, denied the request due to increased risk of death and injury.
Despite NHTSA's denial of the petition, 9 states (Colorado, Kentucky, Minnesota, Montana, Oklahoma, Oregon, Tennessee, Texas, and Washington) have adopted a definition of "medium-speed vehicle (MSV)" and all except Colorado allow MSVs on specified portions of their public roads. Colorado's law states that medium-speed vehicles cannot be titled or registered until the National Highway Traffic Safety Administration has adopted safety standards for vehicles that operate at greater than 25 mph but less than 45 mph.
For details, go to http://www.iihs.org/laws/mediumspeedvehicles.aspx