While driving in the city, the energy needed to overcome the rolling and aerodynamic resistance is (per kilometer traveled) about half the resistance during the highway part of the NEDC. Nevertheless the fuel consumption of a conventional vehicle is much higher when driving in the city. This is largely due to the strong part load operation of the engine. Also the lack of energy recuperation and the idle losses of the engine contribute to a high specific fuel consumption.
In the HyDrid, the engine operation is not determined by the load at the wheels but has the task to keep the pressure in the accumulator between a certain band width. The engine torque is directly related to the pressure in the high pressure accumulator and can consequently only vary between 50% (at 200 bar) and 100% (at 400 bar) of the maximum torque. Operation of the engine at low loads -and at a low efficiency- is therefore completely avoided.