The Technical University of Berlin has designed a three-wheeled car called CLEVER or Compact Low Emission Vehicle. It is an urban transport that runs on compressed natural gas and gets 188 miles per gallon. The car measures 10'L x 3.3'W x 4.4'H and will cost $10,000 when it is produced.
An inherent problem with vehicles designed like this three-wheeler, is tipping while cornering. The design engineers solved this problem with a clever (no pun intended) built-in lean. The same thing motorcyclists do during cornering.