Speeding

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The speed at which a driver or rider chooses to travel on the road affects both the risk of a crash occurring and the severity of any resulting injuries.

Research has identified excessive speed as a major factor in approximately 20% of fatal crashes in Australia.

However, the links between speed and road safety are complex and speed could be a factor in as many as 50% or more of road crashes. In fact, in just about any crash, the faster you travel the harder you hit, and the more serious the injury risk.

There are two kinds of speed problem:

• excessive speed (travelling faster than the speed limit)
• inappropriate speed (travelling too fast for the conditions).

Speed limits are set so as to indicate a reasonable speed for most vehicles under normal circumstances. But, under less than ideal conditions, travelling below the speed limit may be required for safety.

Speed and crash risk
Research at the University of Adelaide has shown that crash risk increases rapidly with increasing speed on both urban and rural roads.

On 60 km/h urban roads the risk of a casualty crash doubles for each 5 km/h above the speed limit; on rural roads the risk doubles for each 10 km/h above the average traffic speed. International research in a number of countries broadly supports these findings.

How can we stop speeding? These are just some of the ideas being considered for future action plans to reduce road trauma in our State: Legislation – more regulations to control speeding Education – more information about the consequences Enforcement – greater use of speed guns and cameras Penalties – increased demerit points and greater chance of losing your licence Traffic management – wider application of lower speed limits Smart technology – vehicle and traffic management systems to automatically lower speed.

Image provided by South Australia Police

Some recent initiatives in South Australia are:

• A general 50 km/h limit now applies throughout urban areas, except on arterial roads and where local councils have established 40 km/h zones
• Speed limits on sections of the Adelaide Hills have been lowered to 80 km/h
• Speed limits on lower standard rural open roads have been reduced from 110 to 100 km/h
• Demerit points as well as fines now apply to speed camera offences.

Our attitudes towards speeding
Almost all drivers and riders exceed the speed limit at some time. Recognition by road users of the involvement of travel speed in road trauma today, is probably at a similar stage to recognition of the involvement of drink driving, twenty or thirty years ago.

Understanding the role of speed in road safety is growing rapidly but much remains to be done to translate that knowledge into effective speed management strategies.

Increasing compliance with speed limits requires:

• strategies aimed at changing community speed behaviour and attitudes towards speeding
• extending the use of education and publicity campaigns integrated with enforcement
• improving enforcement practices
• changing penalties to increase their effectiveness in deterring speeding.

Stopping distance
Higher travelling speed increases the risk of crashes and the severity of the resulting injuries by increasing reaction distance, braking distance, impact speed, crash energy, and the chance of losing control.

Small reductions in travel speeds can make a big difference to impact speeds which, in turn, have a big effect on the risk of death or serious injury. For example, the point where a vehicle travelling at 50km/h could stop under emergency braking conditions (perhaps just avoiding a collision) a vehicle travelling at 60km/h would still be travelling at more than 40 km/h.

Other road users are more likely to underestimate the approach speed of a vehicle that is travelling much faster than other traffic, and turn across its path. Higher speed also means they have less time to get out of harm’s way.

Pedestrian safety
Increased walking is encouraged for its health and fitness benefits, and as a traffic reduction measure. But pedestrians are vulnerable road users and represent about 15% of the road toll. The three highest risk groups are children, the elderly, and those affected by alcohol.

Research has shown that the risk of severe injury or death for pedestrians increases rapidly between collision speeds of 40 to 60 km/h. Even small reductions in urban speeds can have a large effect on the risk of a pedestrian fatality.

Reducing traffic volumes and speeds, particularly where there is significant pedestrian activity, would provide substantial improvements in amenity and safety. Research has shown that lowering speed limits on urban arterial roads would result in a greater reduction in pedestrian casualties than the same lowering of limits on residential streets.

Crash energy - Safety Science
Higher travelling speeds result in higher collision speeds which produce disproportionately more severe injuries. The severity of injuries sustained in a crash is, other things being equal, always dependent on the energy that is dissipated in the crash.

Crash energy increases at a much faster rate than collision speed - it increases in proportion to the square of the change in collision speed. For example, a 10% increase in collision speed, say from 100 to 110 km/h, increases crash energy by 21%.

As speeds increase, serious injuries are usually found to increase at a faster rate than less serious injuries.

Why regulate speed?

• To promote the interests of the whole community ahead of the interests of individuals
• To protect individuals from the risky behaviour of others
• To protect individuals from their own fallibility, given that the risks associated with certain behaviours are often not recognised by those who engage in such risky behaviours.

An important reason underlying the regulation of speed on all parts of the road network is the divergence of the private and social impacts of speeds.

Individual drivers do not accurately perceive all of the impacts of higher speeds. Higher speed means shorter travel time - which is readily perceived and valued by travellers. But higher speeds also lead to increased vehicle operating costs and emissions (which are less obvious) and a greatly increased risk of crash and injury.

As a consequence of their unbalanced perception of the impacts of speeds, drivers tend to prefer travel speeds higher than would be optimal for society. This is why speed management strategies nearly always focus on limiting or reducing travel speeds.

Rural open road crashes
Excessive speed (exceeding the limit) and inappropriate speed (too fast for the conditions) are often important factors in single vehicle crashes such as hitting a fixed object and rolling over, particularly on the open road in the country.

Other important information

For more information, visit the Department of Planning, Transport and Infrastructure website.