Crushing the road toll

May 2005

Slowing traffic might be unpopular but it is reducing the road toll. Leading Accident Research expert Professor Ian Johnston explains why speed management is so controversial.

Slowing traffic is anathema as public policy. Our society glorifies speed in vehicle advertising, in film and in motor sports and seeks ever-shorter journey times. And the research community finds itself walking the tightrope of evidence advocacy across the abyss of political and community controversy.

Professor Ian Johnston: the Accident Research Centre has played a crucial role in helping reduce Victoria's road toll -- and the work continues.

Nowhere has this balancing act been more difficult than with the current debate over speed management.

Australia -- and Victoria in particular -- has an international reputation for leading the way in reducing death and serious injury from road traffic crashes.

From the shocking peak of 1970, when more than 1000 Victorians lost their lives, road deaths were reduced to fewer than 350 in 2004. The death rate has fallen from almost 31 per 100,000 persons to fewer than eight.

Until the late 1960s/early 1970s, road safety policy lacked an evidence base. But over the next decade the discipline of 'traffic safety science' emerged -- not a science in its own right but a confluence of the disciplines of epidemiology, public health, engineering, psychology, mathematics and statistics, and trauma medicine.

Traffic safety problems began to be identified and analysed, intervention options were assessed for likely effectiveness, and intervention programs were evaluated and modified. The public policy process gradually took root in the rapidly expanding base of scientific knowledge.

The Monash University Accident Research Centre was established in the second half of the 1980s as a partnership between the Victorian Government and the university to help develop an independent evidence base for preventing and controlling injury in all its settings, not just on the road.

The controversy over speed management

Injury occurs when energy impacts a human beyond the body's bio-mechanical tolerances. Injury prevention is therefore about managing the exchange of (mostly kinetic) energy between the environment and the human. Crash prevention precludes energy exchange while injury prevention is directed at minimising energy exchange in the event of a crash.

No one disputes that the higher the speed at impact, the greater the likelihood of injury. But there is robust debate over the nature of the relationship between travel speed and the risk of crash involvement.

The crashworthiness of vehicles has improved dramatically in recent years. Nevertheless there are limits on the levels of protection offered -- limits that are poorly understood by the community.

Pedestrians are the most vulnerable to injury, and the relationship between impact speed and the probability of death is dramatic.

Even a vehicle occupant protected by seat belts, airbags and energy-absorbing vehicle structures can only survive a frontal crash up to around 70 km/h, and only around 50 km/h if the vehicle is struck in the side, where the engineering options for energy attenuation are more difficult.

Further gains in passenger vehicle crashworthiness will occur but they will be incremental, especially as the frequency of crashes between vehicles of unequal mass increases, driven by the disparate growth in 4WDs and commercial vehicles.

The research evidence for a relationship between travel speed and crash likelihood comes principally from case-control studies.

There is no longer any doubt that an exponential relationship exists between travel speed and the probability of involvement in an injury-producing crash, though the precise form of the relative risk curve remains uncertain.

And, of course, that is precisely where the controversy lies -- what is the threshold increase in relative risk that warrants government enforcement action?

Victoria's progress in reducing road deaths had stalled during the 1990s, reaching a new 10-year 'high' (of 441) in 2001. MUARC was invited to suggest a way forward.

Given the evidence of the relationship between travel speed and crash probability, the low impact speed thresholds for pedestrian injury and the frequency of death and injury in metropolitan Melbourne, MUARC recommended speed reduction measures, estimating that a reduction of even a few kilometres per hour in average urban travel speeds would lead to a significant overall reduction in deaths and serious injury.

The Victorian Government then:

• reduced the general urban speed limit from 60 to 50 km/h;
• removed the 'enforcement tolerance' (previously there was a tolerance of around 10 per cent or 10 km/h above the limit before a speeding ticket was issued, making the effective speed limit well above the posted limit);
• dramatically increased the level of enforcement by mobile speed cameras;
• made the enforcement more covert (based on MUARC research of effectiveness); and
• supported the program with extensive public education campaigns.

The package was highly controversial, and MUARC's research and its interpretation of the research literature came under heavy public criticism. However, the proof of the pudding has been in the eating. Deaths in 2003 (330) and 2004 (343) have been the lowest ever recorded in Victoria.

And the research has withstood the vigorous challenge.

Action: Visit the MUARC website.

Victorian Road Toll Figures

Source: Transport Accident Commission

1970 - seat belt wearing made mandatory 1987 - MUARC established 2001 - a 50 km/h default speed limit introduced

A text description of this graph is also available.