Michigan just reclassified its operator licensing requirements for three-wheeled vehicles like the Polaris Slingshot. (Now called Autocycles) Drivers no longer need a motorcycle license to operate one in Michigan

Michigan law defines an autocycle as “an enclosed motorcycle that is equipped with safety belts, rollbar, windshield wipers, steering wheel, and equipment otherwise required on a motorcycle, and which has not more than three wheels in contact with the roadway at any one time.”

Laws still vary from state to state, but at least 31 require an autocycle to have three wheels and 27 require a steering wheel.

http://www.motortrend.com/news/autocycles-gain-ground-38-states/