Perhaps the most important vehicle on display at last week's Auto Africa 98 show was Toyota's Prius hybrid car. But what makes the Toyota Prius important is that it is the first volume-produced hybrid passenger car, with 13 000 sold in Japan since December 1997. The Prius makes continuously varied use of both petrol and electric motors, depending on driving conditions. When the car comes to rest, the petrol engine is automatically shut down, so there are no idling emissions. Idling and initial pull-off burn fuel less efficiently than when under steady load, and therefore produce dirtier emissions. On pull-off, the Prius uses the electric motor, making maximum use of the fact that electric motors deliver maximum torque instantly, whereas internal combustion engines need to build up revs to generate full pulling power.