Using GPS Probe Speed Data to Estimate the Attribution of Speeding on Casualty Crashes: A Case Study in Queensland

Abstract

While the relationship between vehicle speed and crash risk and severity are well understood, precise quantification of the attribution of speeding to casualty crashes remains elusive, due in part to the lack of reliable network-wide speed survey data. A relatively new source of network-wide speed data is Global Positioning System (GPS) probe data. This paper explores the feasibility of using these data, along with existing crash risk estimates, to determine the proportion of casualty crashes attributable to travelling at various speeds above the posted limit on Queensland roads. Findings were generally consistent with other data sources, highlighting the danger associated with high-level speeding (more than 20 km/h over the speed limit), estimating that up to 32.5% of all casualty crashes were attributable to this behaviour. Analyses also showed the risks associated with low-level speeding (1-10km/h over the limit), with up to 19.2% of all casualty crashes estimated to be attributable to such behaviour. The implications of these findings on road safety are discussed. Notwithstanding the limitations of GPS speed probe data, the findings suggest that it represents a promising source of network-wide speed data for estimating the attribution of speeding in casualty crashes. Efforts should be made to improve the reliability of these data by increasing the representativeness of vehicles contributing to the data.