I think it uses an electric motor below 18 mph, not the other way round. Above that speed the diesel engine drives the car and generates electricity to recharge the batteries. It's a shame however that it uses a diesel engine as it is diesel fumes from busses, black taxis and delivery vehicles that are killing us i.e. diesel particulates. This is why pedestrianisation of the city centre must become a priority and busses such as the Metroshuttle should be all converted to LPG. We used to have "trolley busses" i.e. electric, quiet and no pollution in the street and we replaced them with ear popping diesel belching busses that ruin the street environment, that is another example of so called "progress". Some cities such as Seattle have gone back to trolley busses.