Effects of automatic emergency braking systems to reduce risk of crash and serious injuries among pedestrians and bicyclists
Authors: Amin Khabat , Kullgren Anders , Tingvall Claes 
Published: February 2025

Objective:  The aim of this study is to investigate the effectiveness of Automatic Emergency Braking (AEB) with detection of pedestrians and bicyclists in reducing car-to-pedestrian and car-to-bicyclists collisions and also injury mitigation in these collisions.
Methods: The study analyses collision data from the Swedish Traffic Accident Data Acquisition (STRADA) encompassing road traffic accidents reported by the police and by emergency hospitals in Sweden. Crashes occurring between the years 2012 and 2022 and with cars from model years 2012 to 2022 were included in the dataset. Two statistical analyses were performed. To evaluate the crash reduction effect of AEB, odds ratio calculations with an induced exposure approach was conducted where the outcomes of sensitive and non-sensitive crashes were studied. The sensitive crashes were hit pedestrians and bicyclists, respectively. The non-sensitive crash type in both comparisons was struck vehicles in rear-end crashes. The collision reducing effect was analysed for various speed limits, lighting and visibility conditions. To evaluate whether AEB has a reducing effect on injury severity, relative differences in injury outcomes (both proportion of MAIS3+ and risk of permanent impairment, RPMI) of pedestrians and bicyclist was compared for hitting cars with and without AEB.
Results: A total of 2 160 pedestrian collisions and 3 374 cyclist collisions were included, and the non-sensitive crashes consisted of 5 738 vehicles. The overall reduction in crash risk was approximately 20% (±10%) for vehicles equipped with AEB with pedestrian and/or bicycle detection. When analysed by lighting conditions, reductions in crash risk of just over 20% were observed in daylight for vehicles with AEB with pedestrian and/or bicycle detection. It appears to be a reduction also in darkness, although the reductions found of approximately 20% were not statistically significant. Reductions were observed for various weather conditions, except for cyclist crashes during rain, fog, and snowfall. A greater reduction in crash risk was noted on high-speed roads (60–120 km/h) for vehicles equipped with AEB for bicycle detection compared to low-speed roads (10–50 km/h). No similar difference was observed for AEB with pedestrian detection. Additionally, there was a greater reduction in crashes at intersections for vehicles with AEB for pedestrian detection and on roads for vehicles with AEB for bicycle detection. No difference in injury severity, both regarding proportion of MAIS3+ and RPMI, for both pedestrians and bicyclists was observed between collisions involving vehicles with and without AEB.
Conclusions: This study confirms the significant potential of AEB systems in improving road safety for pedestrians and cyclists. However, their current effectiveness is too low to provide sufficient protection at today's speed limits and their expected potential and real-world performance differ a lot, which highlights the need for improvements. The study shows varying effectiveness of AEB systems in reducing crash risks under different lighting, weather, and speed conditions. Furthermore, no injury mitigating effect could be verified for cars with AEB for pedestrians and bicyclist possibly showing that either a crash was completely avoided, or the AEB system did not perform any braking. While avoiding crashes could be the prime objective for an AEB for vulnerable road users, braking that reduce injury severity despite there was a crash is of importance as well.