Modelling E-scooterist Braking and Steering for Collision Avoidance

Licentiate thesis, 2024

Introduction: In the last few years, new road safety issues have emerged with the growing popularity of novel micromobility vehicles (MMVs). The term ‘novel MMV’ includes, in addition to electrically assisted bicycles, electric kick scooters (e-scooters) and Segway balance scooters (Segways)—which are usually distinct in appearance and operation from traditional MMVs (conventional bicycles). Developing validated models that offer a comprehensive understanding of the behavior of these new types of MMVs is crucial to inform the design of new, safer MMVs, active safety systems, infrastructure, and the making of regulations. This licentiate thesis includes two studies that shed light on how MMV riders perform longitudinal and lateral control of both traditional and novel MMVs at an operational and tactical level.

Methods: Study 1 analyzed field test data and compared the longitudinal control (i.e., accelerating and braking) of bicycles, an electrically-assisted bicycles (e-bicycle/e-bike), a light personal electric kick scooters, and a Segway balance scooters. Study 2 conducted field tests and compared both the longitudinal and lateral (i.e., steering) maneuvers in a rear-end collision avoidance scenario. A larger e-scooter from the public sharing systems replaced the Segway in the test. Comparisons were made among different types of vehicles, maneuvers, and urgency levels (i.e., maneuver comfortably as daily riding, or harshly as avoiding close danger), to determine the extent to which these novel MMVs, compared to traditional bicycles, demonstrate constraints in maneuverability, safety, and comfort.

Results: The results showed differences in longitudinal performance across vehicles, while no statistically significant differences were observed in lateral performance. Novel MMVs demonstrated poorer braking capability than bicycles and were perceived as less safe and maneuverable. Among the two e-scooters, the larger one could achieve shorter braking distances. Additionally, riders were able to improve their collision-avoidance performance by compromising comfort when urgency increased. Two kinematic models, linear and arctangent, were derived to predict MMV trajectories.

Conclusion: Compared to bicycles, novel MMVs demonstrate statistically significantly poorer in braking performance, which usually constrains the rider’s collision avoidance capability. No statistically significant difference was observed in steering. The findings of this thesis have implications for improving road safety for MMVs by informing MMV design, infrastructure planning, policy-making, and consumer assessment programs. For example, EuroNCAP can incorporate the findings to design test scenarios for this new group of vulnerable road users (VRUs). They can also support the development of active safety systems and automated driving features for automobiles, enabling more accurate and acceptable system activations with respect to timing and magnitude in itneractions with MMVs.