This first of the New Bus 4 London has been running for a while on route 38. Like the old Routmaster, now withdrawn from service, one can hop on and off at the rear but on this new bus there are doors in the centre and at the front as well.. More are on order and due to be delivered in April 2013. This fulfills a commitment made by Boris Johnson during his successful campaign to become mayor of London. This new bus is a hybrid drive, using an electric motor normally running from a battery charged by a diesel generator and also energy from regenerative braking. This type of energy conserving system is used in F1 motor sport as KERS (kinetic energy recovery system). Some cars also use regenerative braking, for example the Toyota Prius and the Honda Insight to economize on fuel use.