Head and thorax impact conditions in bicycle and e-scooter collisions with cars: Insights from an extensive multibody simulation dataset

Introduction:The rapid growth of bicycle and e-scooter use has led to an increase in related injuries, with the most severe affecting the head and, less often, the thorax during collisions with cars. Although both groups use the same helmets, impact conditions remain insufficiently documented to evaluate current protections or determine whether their requirements should differ. To address this gap, this work aims to characterize head and thorax impacts during bicycle– and e-scooter–car collisions. Method: A full-factorial accident-reconstruction study using multibody simulations was conducted to assess the effects of crash configuration (crash scenarios, vehicle types, speeds, etc.) on impact chronology, impact velocity, impacted body regions, and injury metrics (peak accelerations, HIC₁₅, thoracic Con3ms) of the head and thorax for impacts with both the car and the ground. Results: Across 2,475 simulations, e-scooter riders showed higher normal head impact velocities than cyclists (median 4.2 vs 3.2 m/s for car impacts and 3.3 vs 3.1 m/s for ground impacts), while cyclists exhibited higher tangential velocities. Similar trends were found for the thorax. These differences led to greater injury severity for e-scooter riders, who reached a median HIC₁₅ of 1,810 compared with 1,347 for cyclists, with the highest values most often occurring during ground impacts. Higher vehicle speed, e-scooter use, SUV involvement, and “head-on” or “side-on-head” scenarios were associated with increased normal head and thorax impact velocities, as well as higher HIC. Conclusions and Practical Applications: These findings are highly valuable for the design and evaluation of targeted protective technologies for bicyclists and e-scooter users.