Testing the acceptability of motorcycle-AEB system: Use of unanticipated interventions as a reliable surrogate of genuinely unexpected events

Objective: Active safety systems such as motorcycle autonomous emergency braking (MAEB) capable of ensuring effectiveness and safe rider-vehicle interaction present many potential benefits to reduce road fatalities but also many challenges. The whole development cycle of MAEB requires research through extensive field tests that reproduce unexpected interventions or real-life driving situation before the system can be available to the end-user. This study aims to better understand the rider's kinematic response required to control the stability of the rider-motorcycle system, as well as the extent of unexpectedness perceived by participants under different degrees of awareness of automatic braking (AB) activation. Methods: We compared responses to AB in anticipated and (un)anticipated conditions and in a condition that was intended to be genuinely unexpected (Out of the Blue). Twenty men and women, wearing an inertial measurement unit on their upper-back, rode a scooter-type motorcycle with two front wheels simulating urban riding maneuvers on a closed test-track. Three automatic braking (AB) profiles were tested in different sessions, ranged from 3 to 5 m/s2 deceleration and 15 to 25 m/s3 braking-jerk. Differences between AB conditions were analyzed using linear mixed models. Results: The unanticipated condition was perceived as fairly unexpected (rated between Quite Unexpected and Very Unexpected). Out of the Blue condition was on average close to the highest level of unexpectedness (Completely Unexpected). The exposure to unanticipated AB events resulted in upper-body response with larger peaks of pitch rate (0.20 to 0.77 rad/s higher) and acceleration (1.0 to 2.3 m/s2 higher) than those of anticipated. Participants showed less postural stability during unanticipated events taking longer both to start correcting the initial forward lean and to fully stabilize balance. Unanticipated and Out of the Blue conditions did not differ in either the amplitude of the kinematic variables or the time-to-peak pitch rate. Conclusions: The kinematic response of the rider's upper-body was found to be a reliable estimator of unexpectedness in AB. The findings suggest that unanticipated AB events while the rider engages in riding tasks can enable testing aimed at designing MAEB systems and assessing end-user acceptance in a reliable manner and within ethical safety limits.