Abstract
The aim of this study is to develop the power model of the relationship between speed and traffic safety. As the inter-urban roads are characterised with heterogeneous traffic, the heterogeneity became the focus of the analysis. The present study analysed the effects of various types of vehicles through a number of speed change combinations and developed six equations: number of fatal accidents, number of fatalities, number of fatal and serious injury accidents, number of fatal or serious injuries, number of injury accidents and number of injured road users. The results indicated that the Power Model showed high predictability of the speed-accident relationship. The models fit the data well with Rsq in the range of 0.6-0.8. The vehicle category-specific ratio power models exhibited how traffic heterogeneity accounts for traffic safety. The equations' power varies with the types of vehicles, indicating the different sensitivity of accidents and casualties to the speed ratios. Overall, with the power estimates around one, except for all injured victims, the estimates were systematically smaller than those that were initially inferred in Nilsson's Power model. The values indicated that the increase in speed determined the increase in the number of accidents and casualties from year to year. The present study successfully developed the first speed-traffic safety Power Model for Indonesia. As it is exclusively dependent on the speed changes, the model can well describe the direction of change in traffic safety irrespective of other changes in the driving environment factors.
Highlights
Speed has been regarded as the primary indicator of safety
The potential mass deformation increases with kinetic energy which is proportional to the vehicle speed squared
While estimates of Nilsson's equations provide vital benchmarks previously not available for Indonesia, the present study's more significant contribution is the analysis of the power of alternative predictors, including six vehicle category-specific ratios of average speeds
Summary
Speed has been regarded as the primary indicator of safety. The kinetic energy dissipates through friction and mass deformation. The potential mass deformation increases with kinetic energy which is proportional to the vehicle speed squared. Studies on how speed is related to safety have been an interesting area in the traffic safety field. Various regressions with different predictors have been analysed and tested to produce the most satisfying relationship and to demonstrate the magnitude of speed effects in accident occurrences and accident severity. The study by [1] reviewed a number of studies on accident risks and confirmed the high relationship. It was found that a big speed difference is related to the high accident number. Gargoum and El-Basyouny [2]
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