Modelling of Some Major Factors Influencing Road Trauma Trends in Victoria 1989-93

Monash University Accident Research Centre - Report #74 - 1995

Authors: S. Newstead, M. Cameron, S. Gantzer & P. Vulcan

Full report in .pdf format [3.1MB]

Executive Summary

A number of recent studies in Victoria have evaluated the effects of countermeasures and other factors which appear to be responsible for the substantial reduction in road trauma since 1989. These include:

  • Increased random breath testing, supported by mass media publicity
  • New speed cameras, supported by mass media publicity
  • Reduced economic activity
  • Reduced alcohol sales
  • Improvements to the road system through treatment of accident black spots
  • Bicycle helmet wearing law
  • Lowering of 110 km/h freeway speed limit

A need was identified to combine the results of these studies into a single model which could explain the overall reduction. This report aims to develop an understanding of how some of the various factors/countermeasures have interacted to produce this reduction. Models developed in the evaluation of the first two countermeasures, estimated from monthly crash data covering the period 1983-92, were consolidated to estimate the effects on serious casualty crashes during each of the years 1990-92. The contributions of random breath testing, speed camera operations, road safety television publicity, unemployment rates and alcohol sales were estimated. Whilst the contributions of the last three countermeasures listed above were not estimated explicitly, their contributions to reducing crashes were accounted for in the general trend component of the models.

The models estimating reductions in serious casualty crashes due to various factors were then validated using 1993 monthly crash data. This was done in two ways. Firstly the models estimating serious casualty crash variations over the period 1983-92 were extrapolated to estimate the monthly number of crashes occurring in 1993. These estimates showed close conformity to the actual monthly numbers of serious casualty crashes observed. Secondly, the models were re-estimated on data covering the period 1983-93 and the parameter estimates compared with those from the old models. None of the parameter estimates experienced statistically significantly change when the models were re-estimated on the 1983-93 data. Subsequently, the contributions of random breath testing, speed camera tickets issued, levels of road safety television publicity, unemployment rates and alcohol sales to reducing the number of serious casualty crashes were estimated for the period 1990-93. A method of separately estimating the effect of accident black spot treatments and disaggregating this from the trend was described and applied.

As an example of application of the modelling procedure to a crash sub-group, the methods were applied to serious casualty crashes over the period 1983-93 involving at least one driver in the age range 17 to 25 inclusive. The contributions of the same road safety programs and socio-economic factors to reducing the number of serious casualty crashes involving young drivers were estimated for the period 1990-93.

Sponsoring Organisation: Baseline Research Program - Department of Justice, Transport Accident Commission, Royal Automobile Club of Victoria (RACV) Ltd, VicRoads