Toyota debuted the new Prius (2010 US model year) at the 2009 North American International Auto Show, and sales began in Japan on May 18, 2009. Its new body design is more aerodynamic, with the coefficient of drag reduced to 0.25 Cd. An underbody rear fin helps stabilize the vehicle at higher speeds.The estimated fuel-efficiency rating using the U.S. EPA combined cycle is: 50 mpg-US (4.7 L/100 km