Car Accident Newsroom

Traveling Speed And The Risk Of Crash Involvement

The main aim of this project was to quantify the relationship between free travelling speed and the risk of involvement in a casualty crash, for sober drivers of cars in 60 km/h speed limit zones in the Adelaide metropolitan area.

The secondary aims of the project were to examine the effect of hypothetical speed reductions on the crashes in this study and to explore the relationship between travelling speed and driver blood alcohol concentration.

Using a case-control study design, the speeds of cars involved in casualty crashes were compared with the speeds of cars not involved in crashes but travelling in the same direction, at the same location, time of day, day of week, and time of year. The conditions imposed on the selection of case vehicles were designed to ensure that the study would yield valid estimates of the relative risk of a car travelling at a free speed in a 60 km/h zone becoming involved in a casualty crash compared to the risk for a car travelling at 60 km/h. Data collection was concentrated during the hours of 9:30am-4:30pm, Monday to Friday as these times had the highest number of non-alcohol-related crashes in Adelaide. Some cases were also collected at nights and on weekends.

The pre-crash travelling speeds of the case vehicles were determined using computer-aided accident reconstruction techniques. This was made possible by the detailed investigation of each crash at the scene which provided the physical evidence needed for input to the computer reconstruction program (M-SMAC).

Additional information about the effects of travelling speed was obtained by calculating what the results of the crash would have been if the case vehicle had been travelling at a different speed.

A separate study was set up to measure the relationship between blood alcohol concentration and travelling speed. The speed of an approaching car was measured 200-300 metres before a signalised intersection using a laser speed meter. When the car stopped at this intersection for a red light, the driver was approached and asked to blow into a breath alcohol meter.