Travel speed and the risk of serious injury in vehicle crashes.

While there is a large quantity of prior research on speed and road safety, no previous studies have quantified the absolute risk of serious injury in a crash relative to travel speed. This study aimed to produce risk curves that relate travel speed to the risk of serious injury in light vehicle impacts in order to contribute to the process of selecting acceptable travel speeds. Serious injury was defined in this study as any injury having a maximum abbreviated injury scale (MAIS) of three or greater, or a fatal injury (MAIS3+F). In the context of a crash, travel speed is defined as the vehicle's speed before the driver reacts to the crash situation. Travel speed was determined by selecting the highest pre-impact speed recorded by an Event Data Recorder (EDR) in the seconds before the crash. A total of 1,618 light vehicle impacts were analysed using logistic regression. Individual risk curves were produced for front, head on, side, rear and single vehicle impacts. The analysis found significant positive relationships between the risk of serious injury and travel speed for all of these impact types. The travel speeds at which the risk of serious injury reached one per cent were 63 km/h across all impacts, 17 km/h for head on impacts, 48 km/h for single vehicle impacts, 58 km/h for side impacts, 81 km/h for front impacts and 96 km/h for rear impacts. These results have implications for the setting of speed limits and other measures that influence the speed at which vehicles travel.

Impact speed and the risk of serious injury in vehicle crashes.

The current guiding philosophies in road safety have stated aims of zero deaths and serious injuries. Speed has previously been highlighted as a key factor in the outcome of a crash but the literature to date has yet to provide a robust relationship between impact speed and the risk of serious injury for crashes other than pedestrian crashes. This study aimed to determine the relationship between impact speed and the risk of serious injury in light vehicle crashes. Crash data from the US based National Automotive Sampling System - Crashworthiness Data System collected from 2011 to 2015 were used in the analysis when there was a known impact speed from an event data recorder (EDR) and a known injury outcome. The analysis was conducted at the vehicle level. Data from a total of 1274 vehicles were used in logistic regressions, with the presence or absence of a serious injury as the binary dependent variable, and impact speed as the continuous independent variable. Individual risk curves were produced for front, side, rear and head on impacts. Impact speed was found to have a highly significant positive relationship to risk of serious injury for all impact types examined. The risk of serious injury reaches 1% at 28 km/h for head on impacts, 51 km/h for side impacts, 64 km/h for front impacts, and 67 km/h for rear impacts. The results emphasise the importance of measures that reduce impact speeds, be they road designs, vehicle technologies or enforced speed limit reductions, and highlight the need to prevent head on impacts.

Safe speed limits for a safe system: The relationship between speed limit and fatal crash rate for different crash types.

OBJECTIVE: The objective of this article is to provide empirical evidence for safe speed limits that will meet the objectives of the Safe System by examining the relationship between speed limit and injury severity for different crash types, using police-reported crash data. METHOD: Police-reported crashes from 2 Australian jurisdictions were used to calculate a fatal crash rate by speed limit and crash type. Example safe speed limits were defined using threshold risk levels. RESULTS: A positive exponential relationship between speed limit and fatality rate was found. For an example fatality rate threshold of 1 in 100 crashes it was found that safe speed limits are 40 km/h for pedestrian crashes; 50 km/h for head-on crashes; 60 km/h for hit fixed object crashes; 80 km/h for right angle, right turn, and left road/rollover crashes; and 110 km/h or more for rear-end crashes. CONCLUSIONS: The positive exponential relationship between speed limit and fatal crash rate is consistent with prior research into speed and crash risk. The results indicate that speed zones of 100 km/h or more only meet the objectives of the Safe System, with regard to fatal crashes, where all crash types except rear-end crashes are exceedingly rare, such as on a high standard restricted access highway with a safe roadside design.