So why, after years of drilling home the warnings, does the law appear to be playing catch-up?
One reason for the apparent reluctance of Westminster to revise the current 80mg alcohol limit is that it seems to play a role in cutting the number of drink-related accidents, with fatalities in Scotland falling by a half between 1997 and 2007.
There is concern that, if the law shifts to enforcing a 50mg limit – equivalent to about a pint of lager for the average male – with a “gradiated” system of penalties, the clarity of the UK’s anti-drink drive messages could be diluted.
“We have a very simple system in the UK: there is a very high alcohol limit with very severe penalties for breaching it,” Neil Greig, head of policy at the Institute of Advanced Motorists, said.
“We have to be very careful we don’t lose the clear message that we have. We also need to enforce the current limit properly so drivers feel they will be caught and I’m not sure we’ve done that yet.”
The problems associated with establishing and enforcing drug driving limits are potentially even more intractable. At the moment, drivers can be prosecuted for taking drugs only if their driving can be shown to have been dangerous – not on the basis of someone simply being under the influence. Amending this, it is argued, would ensure a more preventative approach that would lead to more prosecutions.
But unlike alcohol, whose presence is relatively easy to trace in the bloodstream, measuring the psychoactive elements of drugs – and their effect on driving ability is far from straightforward.
Equipment allowing police to conduct roadside tests for drug levels is still being developed and would need to be modified to tie in with laws once they are established.
Road safety groups have also voiced concern that a “safe limit” for drug taking would send out the wrong message. “We need to have a debate about whether having taken an illegal substance is in itself an offence or are there safe limits. If you start saying that X amount of cannabis doesn’t affect driving you’re condoning having an illegal substance in the blood,” Mr Greig added.
But despite the difficulties, motoring organisations and road safety groups claim there is a strong case for reducing current alcohol limits.
A spokesman for the RAC said the 80mg limit was “confusing” for drivers. “The advantage of a 50mg limit is that, for the average male, it equates pretty much to a pint of lager, so it’s clear where the boundary is. The problem with the 80mg limit is that it’s more confusing and people are more likely to end up taking risks,” he said.
Robert Gifford, executive director of the Parliamentary Advisory Council for Transport Safety, said that drink and drug-driving were “key issues” for road safety over the next decade.
“The link between alcohol and crash involvement is well-known and the research is uncontested. Analysis concluded that around 65 lives a year would be saved with a lower drink-drive limit.”
The review ordered yesterday by the Department for Transport was also welcomed by Mary Williams, chief executive of road safety charity Brake, who said: “We urgently
need effective road-side tests for drugs and a law banning drug-driving, as well as random testing of drivers for drink and drugs and tougher measures to stop offenders, such as life-long bans.”