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APPENDIX
E
At the public hearing Dr B. Fildes, a senior research fellow at the Monash University Accident Research Centre (MUARC), presented several diagrams that are fundamental to speed-related crashes.
Dr Fildes said there are two fundamental issues in terms of speed and crashes:
He said those two issues are fundamentally different and the level of knowledge on them is quite different.
The first diagram (Figure E.1) shows old research undertaken in 1964 by Solomon who worked in the United States of America transportation authority. [1] He proposed that the relationship between speed and crash involvement is a function of the variation of one's speed from the average speed at a particular site. He reported a U-shaped relationship which, although not perfectly true, shows that the further one moves away from the average travel speed the more likely one is to have a crash.
The study was based only on United States rural highways and the method of determining the speed of crash-involved vehicles has been criticised.
MUARC undertook a study with VicRoads during the late 1980s and early 1990s where vehicle speeds were observed and then drivers were interviewed further down the road without telling them that their speed had been observed. [2] The stated accident history was then related to their speed. The comparison is shown on the diagram for both rural and urban sites. Generally, when travelling above the mean speed of traffic the risk of crashing increases. It is not as marked as Solomon's, but there is not much data available. Nevertheless it fails to show any relationship at the lower speed end.
The second diagram (Figure E2) was also the result of research by Solomon. It shows that the faster one collides the more likely one is to suffer an injury (or death). In the particular figure shown the measure is the number of people injured per 100 vehicles involved in crashes.
FIGURE E1
FIGURE E2
FIGURE E3
A further piece of evidence came from Goran Nilsson from the Swedish Road and Traffic Research Institute (VTI) and is shown in Figure E3. Based on information from Scandinavian and other countries it quantifies the likelihood of the number of people killed, seriously injured and all injured if the travel speed is increased or decreased (as a result of speed limit changes). [3]
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