Australian evidence shows there is more to lowering the road toll than simply reducing the legal blood-alcohol limit.
At first glance, statistics from New South Wales look impressive: when it lowered the blood-alcohol limit from 80mg per 100ml of blood to 50mg there was an immediate response -
a fall of 14 per cent in "drinking hour" crashes for men, and 5 per cent for women.
In Victoria, a police traffic alcohol section study reported an "immediate and significant" reduction in deaths involving over-the-limit drivers when the legal limit was lowered to 50mg.
But in both states, the gains were temporary. As had occurred after random breath testing was first introduced in the 1970s, the impact diminished over time.
A Queensland study even found that a "considerable percentage" of 780 motorists surveyed said they had driven while drunk at least once in the previous six months without being detected. Many were not deterred by the fear of breath tests.
An Australian Transport Safety Bureau study said the scale of policing was directly related to the effectiveness of breath tests.
It said that since NSW stepped up enforcement in 1987, results showed that an increase of 1000 in the daily testing rate corresponded roughly to a 6 per cent decline in accidents, rising to 19 per cent for night-time single-vehicle crashes.
Further research showed that drivers were pulled into line for some time after they had been tested, but slipped back into bad habits if they were not stopped again.
The Victorian study said that prevention rather than detection was the key: "The true objective is to create a perception amongst the driving public that if they drink then drive, their apprehension is inevitable. That the threat is real or otherwise is not the point - the key is whether the public believes it to be."
Other studies have shown that a halving of the number of road deaths per 100,000 people since 1970 - despite a significant increase in cars on the road - was the result of a wide range of safety measures and community awareness.
