Hybrid on the hard shoulder

Toyota has begun an investigation into why its Prius petrolelectric hybrid cars might be stalling or shutting off, sometimes at motorway speeds.

No such incidents are believed to have stricken UK drivers, but 13 cases have been reported to the US National Highway Traffic Safety Administration, according to the car maker.

A Toyota GB spokesman said it was too soon to know what might be going wrong with the vehicles, which are capable of more than 65mpg, but US dealers are reported to be pointing the finger at a software problem.

The family-sized Prius is the most fuel-efficient car on the market according to standard European drive-cycle testing, beating even the smallest cars. But while many automotive industry analysts regard the Prius as reliable, some believe the extra cost and complexity of hybrids will limit their market appeal.

Prius’s hybrid drive system relies on sophisticated computer control to maximise the efficiency of its combination of 1.5-litre petrol engine and 50kW electric motor; the two units can drive the car jointly or independently, and batteries are kept charged by engine power and energy recovered through regenerative braking.