REANALYSIS OF TRAVELLING SPEED AND THE RISK OF CRASH INVOLVEMENT IN ADELAIDE, SOUTH AUSTRALIA

Modified logistic regression modeling was used to reanalyze free traveling speed case control data in an urban 60 km/h speed limit environment. An exponential second order polynomial function was used to model the relative risk of being involved in a casualty crash based on free traveling speed. The relative risk was found to approximately double for each 5 km/h increase in free traveling speed. This curve and the original data were then used to estimate the effects of various hypothetical speed reduction scenarios. Illegal speeding was found to be a major factor in casualty crashes and it was found that even very small reductions in the speed of the vehicles in general could be expected to result in a major reduction in the frequency of casualty crashes in an urban area.