 The production design model officially unveiled on September 16 , 2008 , as part of General Motors centennial celebration at the <unk> headquarters in Detroit . The production model differed greatly in design from the original concept car . The carmaker cited necessary aerodynamic changes needed to reduce the concept car 's high drag coefficient of Cd = 0 @.@ 43 down to a more efficient Cd = 0 @.@ 28 , though still somewhat higher than the Toyota Prius Cd = 0 @.@ 25 . Another reason was the use of General Motors ' new global compact vehicle platform Delta II to keep costs reasonable , and shared with the 2010 model year Chevrolet Cruze . Another significant difference from the concept car is the seating , as the production Volt seats four rather than five passengers . This change was due to the higher @-@ than @-@ usual central tunnel that runs from the front console to the rear seat that houses the car 's T @-@ shaped battery pack . 
