Effects of speeding
Speed is a factor in all road deaths and injuries. In Victoria, excessive speed is the primary cause in around one third of road casualties, accounting for close to 100 lives and up to 2000 serious injuries every year.
Even if the primary cause of a crash is not speed, a crash in a slower vehicle will be less severe. Your chances of surviving and avoiding injury are greater the slower you are driving with the chances of being in a crash approximately doubling for every 5 km/h over the limit in a 60 km/h zone.
For every one per cent reduction in average speed, there is on average a three per cent reduction in casualty crashes. These findings underpin the Transport Accident Commission’s 'Wipe off 5' campaign.
See also: Speed Limits
The physics of a crash
In a crash, it is the amount of kinetic energy that is imparted which causes injuries or death. This kinetic energy increases exponentially with speed.
A doubling of speed is not equal to twice as much kinetic energy, but rather a substantial increase much beyond that and much more lethal. A 20 per cent increase in speed is roughly a 45 per cent increase in kinetic energy.
Chances of survival
The chance of death or serious injury changes from minimal to substantial with surprisingly small increases in speed. For example, a person hit by a car at 30 km/h will be severely injured with about a 10 per cent likelihood of death. If that speed is increased to just 55 km/h, the likelihood of death is about 85 per cent.
Pedestrians hit at 60 km/h will not survive. The interactive graph below shows this clearly.
Based on data cited in Monash University Accident Research Centre Report 229 (figure 3.5)
The figures are a bit higher for car occupants, but in general a side impact above 40-50 km/h and a front impact much above 70 km/h are unlikely to be survivable.
These are speeds which occur during a typical urban trip. In the real world, where crashes are usually the result of a complex interaction between a number of factors, getting drivers to reduce speeds by even small amounts will substantially reduce both the number and severity of casualties.
Vulnerable road users
Some people argue that safer cars can counteract the effects of speeding. It is true that new vehicle safety technologies can make crashes less likely and more survivable. However, no technology can completely overcome the laws of physics in terms of stopping distances and the speed/severity relationship.
Moreover, advances in vehicle technology are almost entirely to the advantage of vehicle occupants and not to vulnerable road users such as pedestrians, bicyclists and motorcyclists. For these people, a reduction in the speed of the vehicle which hits them is critical to their survival.
