The utility of historical trends to project future numbers of crashes in South Australia

In this paper, some simple models are examined for their utility in projecting future fatality numbers. Functions that represent the crash rate and travel exposure are fitted to time series of South Australian crash data. The model is used to examine the utility of forecasting crash numbers based on medium to long-term trends. (The model is simple as it does not seek to attribute changes to any set of factors in particular). In addition, South Australian data from 2001-2010 are examined in the light of systematic road safety changes that were made over the period corresponding to the road safety strategy that was active over the period. The results show that fitting models to long-term trends has some utility for future predictions, but actual numbers (and shorter term trends) may significantly deviate from such a model. Furthermore, results indicate that models based on medium-term trends are an imperfect guide to the medium term future. Finally, a discussion about recent features in the time-series of traffic fatalities is given. It is argued that to reach targets that have been set in the 2011-2020 state strategy (no more than 80 deaths per annum by 2020), a reduction in risk similar to that brought about in the previous decade by lowering urban speed limits will have to be achieved. The most effective way of achieving this will be through broadly-based changes to the road transport system that will lower risk for the greatest number of road users within the decade. However, interventions targeting narrowly defined high-risk problems (which may be cost effective) and actions to accelerate the improvement in the average safety of vehicles (which may only yield full benefits beyond the 10 year horizon of the strategy) should also be pursued.Robert Anderso