Transport for London and Metrobus have just taken delivery of the first of seventeen new hybrid double decker buses. The two-story buses have been iconic image of central London for over half a century and now they are rolling forward into the 21st century. The new buses are being built by Alexander Dennis Limited (ADL) using hybrid drive systems from BAE systems. The BAE system is a series hybrid configuration with a diesel about half the size of what's used on a conventional bus driving a generator. The generator feeds the motor that drives the bus with a lithium ion battery pack providing extra juice for acceleration when needed. During regenerative braking the energy goes back to the battery pack. There are currently about 1,500 buses with BAE HybriDrive running in several North American cities.