Injury risk curves to guide safe speed limits on Swedish roads using German crash data supplemented with estimated non-injury crashes.

Vision Zero postulates that no one should be killed or seriously injured in road traffic; therefore, it is necessary to define evidence-based speed limits to mitigate impact severity. The overall aims to guide the definition of safe speeds limits by establishing relations between impact speed and the risk of at-least-moderate (MAIS2+) and at-least-severe (MAIS3+) injuries for car occupants in frontal and side crashes in Sweden. As Swedish in-depth data are unavailable, the first objective was to assess the applicability of German In-depth Accident Study (GIDAS) data to Sweden. The second was to create unconditional injury risk curves (risk of injury given involvement in any crash), rather than risk curves conditional on the GIDAS sampling criterion of suspected-injury crashes. Thirdly, we compared the unconditional and conditional risk curves to quantify the practical implications of this methodological choice. Finally, we provide an example to demonstrate how injury risk curves facilitate the definition of safe, evidence-based speed limits in Sweden. Characteristics important for the injury outcome were similar between GIDAS and Swedish data; therefore, the injury risk curves using German GIDAS data are applicable to Sweden. The regression models yielded the following results for unconditional injury risk curves: 10 % MAIS2+ at 25 km/h impact speed for frontal head-on crashes, 20 km/h for frontal car-to-object crashes, 55 km/h in far-side crashes, and 45 km/h in near-side crashes. A 10 % MAIS3+ risk was reached between 70 and 75 km/h for all crash types. Conditional injury risk curves gave substantially different results; the 10 % MAIS3+ risk in near-side crashes was 140 km/h, twice the unconditional value. For example, if a 10 % MAIS3+ risk was acceptable, treating remaining uncertainty conservatively, assuming compliance with speed limits and that Automated Emergency Braking takes 20 km/h of the travel speed before impact in longitudinal traffic, the safe speed limit for car occupants on most Swedish roads would be 80 km/h and 60 km/h in intersections.

Simulating Automated Emergency Braking with and without Torricelli Vacuum Emergency Braking for cyclists: Effect of brake deceleration and sensor field-of-view on accidents, injuries and fatalities.

This study estimates how many additional cyclist accidents, injuries or fatalities are avoided or mitigated by adding a system which increases braking levels, the Torricelli Vacuum Emergency Brake (VEB), to a state-of-the-art Automated Emergency Braking (AEB) system. To obtain a realistic state-of-the-art AEB system, the AEB parameter settings were defined to fulfil but not exceed the performance necessary to achieve a full score in the European New Car Assessment Program (Euro NCAP). The systems are simulated in a simple but realistic simulation model in MATLAB with varying brake deceleration and sensor field-of-view (FoV). This study utilised data from the German In-Depth Accident Study (GIDAS), released in January 2019, and the related Pre-Crash Matrix (PCM), released in February 2019. Cyclist Injury Risk Curves were created from 2,662 GIDAS accidents involving a passenger car and a cyclist. The sample of cyclist accidents from the GIDAS-PCM database used in the final simulations comprised 1,340 collisions between the front of a passenger car and a cyclist. Both data samples were weighted to be representative of Germany as a whole. Adding the VEB was found to avoid over 20% more accidents than the AEB alone. Although increasing the FoV from 75° to 180° for the AEB system increases its accident avoidance rate to a level comparable to the VEB, the VEB remains about 8-20% more effective in reducing fatalities and injuries, and thus offers greater safety benefits than simply increasing AEB FoV. While the initial accidents in the representative simulation sample are fairly evenly distributed over the vehicle front, the remaining accidents (those that cannot be prevented by AEB or VEB) are more concentrated at the vehicle corners and are further characterized by high cyclist speeds. High cyclist speeds and impact to the vehicle corners potentially increase the relative frequency of head impacts to the stiff A-pillars. We therefore recommend that, for passenger cars, VEB and other advanced AEB systems should be combined with in-crash protection, especially in the A-pillar area, to best protect cyclists from injury.

Real life safety benefits of increasing brake deceleration in car-to-pedestrian accidents: Simulation of Vacuum Emergency Braking.

The objective of this study is to predict the real-life benefits, namely the number of injuries avoided rather than the reduction in impact speed, offered by a Vacuum Emergency Brake (VEB) added to a pedestrian automated emergency braking (AEB) system. We achieve this through the virtual simulation of simplified mathematical models of a system which incorporates expected future advances in technology, such as a wide sensor field of view, and reductions in the time needed for detection, classification, and brake pressure build up. The German In-Depth Accident Study database and the related Pre Crash Matrix, both released in the beginning of 2016, were used for this study and resulted in a final sample of 526 collisions between passenger car fronts and pedestrians. Weight factors were calculated for both simulation model and injury risk curves to make the data representative of Germany as a whole. The accident data was used with a hypothetical AEB system in a simulation model, and injury risk was calculated from the new impact speed using injury risk curves to generate new situations using real accidents. Adding a VEB to a car with pedestrian AEB decreased pedestrian casualties by an additional 8-22%, depending on system setting and injury level, over the AEB-only system. The overall decrease in fatalities was 80-87%, an improvement of 8%. Collision avoidance was improved by 14-28%. VEB with a maximum deceleration in the middle of the modelled performance range has an effectiveness similar to that of an "early activation" system, where the AEB is triggered as early as 2 s before collision. VEB may therefore offer a substantial increase in performance without increasing false positive rates, which earlier AEB activation does. Most collisions and injuries can be avoided when AEB is supplemented by the high performance VEB; remaining cases are characterised by high pedestrian walking speed and late visibility due to view obstructions. VEB is effective in all analysed accident scenarios.