50cc (actually 49.5cc) engines offer the advantage of being classified as a Moped or Scooter engine, and many municlities do not require a specific motorcycle license to operate a vehicles with engines sizes of less than 50cc.
Engines of exactly 50cc (or approximately 49.5cc) are classified as either Mopeds or Scooters, and in most cities, no special motorcycle license is required to operate such vehicles with engines smaller than 50cc.