Effects on crash risk of automatic emergency braking systems for pedestrians and bicyclists

Kullgren, Anders; Amin, Khabat; Tingvall, Claes · 2023 · Crossref

DOI: 10.1080/15389588.2022.2131403

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Summary

This study evaluates the effectiveness of automatic emergency braking (AEB) systems with pedestrian and bicyclist detection in reducing crash risks involving vulnerable road users. Motivated by the persistent high fatality rates among pedestrians and bicyclists in Europe and Sweden, despite overall declines in traffic fatalities, the research aims to quantify the real-world impact of these specific AEB technologies. While earlier AEB systems targeted rear-end collisions, newer iterations are designed to mitigate frontal impacts with vulnerable users, yet empirical data on their efficacy, particularly for bicyclists, had been limited. The researchers utilized data from the Swedish Traffic Accident Data Acquisition (STRADA) register, which includes police-reported accidents and emergency hospital records. The analysis covered crashes occurring between 2015 and 2020 involving cars from model years 2015 to 2020. The study employed an induced exposure approach using odds ratio calculations. This method compares "sensitive" crashes (hits on pedestrians or bicyclists) with "nonsensitive" crashes (rear-end collisions where the vehicle was struck), under the assumption that AEB for frontal vulnerable user detection does not influence the risk of being struck in the rear. The dataset included 712 hit pedestrians, 1,105 hit bicyclists, and 1,978 rear-end crashes. Analyses were stratified by lighting conditions (daylight, twilight, darkness), weather conditions, and road speed limits. The results indicated an overall 8% reduction in crash risk for AEB with pedestrian detection, which was not statistically significant. In contrast, AEB with bicyclist detection showed a statistically significant 21% reduction in crash risk. Performance varied significantly by lighting conditions: no reduction in crash risk was observed for either system in darkness. However, in daylight and twilight, AEB with pedestrian detection reduced crash risk by 18%, and AEB with bicyclist detection reduced it by 23%. Weather analysis revealed a significant 53% reduction in bicyclist crashes during rain, fog, or snowfall, though no other weather-specific reductions were significant. Additionally, greater crash reductions were observed on high-speed roads (50–120 km/h) compared to low-speed roads (10–40 km/h). The study concludes that AEB systems with bicyclist detection are effective in reducing crashes, particularly in daylight and twilight conditions, whereas pedestrian AEB showed limited overall effectiveness. The lack of performance in darkness is a critical limitation, as many pedestrian and bicyclist crashes occur in low-light conditions. The authors suggest that AEB alone is insufficient for full protection and should be combined with infrastructure measures, such as 30 km/h speed limits in mixed-traffic areas, to enhance detection capabilities and reduce impact severity. The findings highlight the need for improved sensor performance in darkness and further research into injury severity outcomes.

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• adas effectiveness

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• Empirical Findings: crash risk outcomes