DRIVERS' scant knowledge of the effects of prescription drugs on their driving ability may mean many drive while unfit, according to research for the RAC.

Many drivers did not know that tranquillisers, anti-depressants or painkillers might mean they could not control a vehicle properly. Three quarters of drivers backed the introduction of a 'traffic light' system on medicine packaging, with red to show that people should not drive when taking a particular drug or green to show that a medicine has no effect on driving ability.