The Volvo B5L Hybrid Double Decker is equipped with a diesel engine with smaller cylinder volume than usual, since it is combined with an electric motor. It is the electric motor that is running the bus when it accelerates to a speed of 15-20 km/h. When the bus is underway, the parallel hybrid system combines diesel and electric power to maintain speed. At higher speeds, the bus uses diesel power alone. Regenerative braking energy charges the battery via the generator. Several of the Volvo hybrid auxiliary systems are powered by independent electric motors. These measures all contribute to high fuel savings on routes with frequent braking and acceleration, like city bus traffic. The parallel hybrid technology reduces fuel consumption and CO2 emissions by up to 35% compared to conventional diesel buses. In the hybrid configuration, the emissions of nitrogen oxide and particulates are reduced by up to 50%.