Crossing in the Dark: The Effect of Vehicle Kinematics and eHMI on Older Pedestrians’ Crossing Behaviour

With higher levels of Automated Vehicles (AVs) entering the traffic system in the future, it is important to investigate pedestrians’ crossing behaviour and experience while interacting with AVs, which lack a human driver. There has been a surge in interest within the last few years in evaluating new forms of communication for AVs, namely external human-machine interfaces (eHMIs). However, much of the research to date has focused on younger pedestrians, and on daytime conditions with optimum visibility. Given that the AVs will interact with pedestrians of all ages, and at all times, there are still key knowledge gaps that need to be addressed. Using the Highly Immersive Kinematic Experimental Research (HIKER) cave-based pedestrian lab, this study investigated the effect of AV kinematics (i.e., deceleration, speed, time gaps) and eHMI presence (a Slow Pulsing Light Band) on the crossing behaviour of younger (18-35 years old) and older pedestrians (64-77 years old), in both daytime and nighttime virtual environments. Results showed that older pedestrians adopted a different crossing strategy to younger pedestrians. If they decided to cross in the non-deceleration trials, they compensated for their longer crossing duration by initiating their crossing earlier than younger pedestrians. However, if they decided to wait until the deceleration was more prominent, before making a crossing decision, they waited longer than the younger pedestrians. Generally, pedestrians reported feeling less safe and behaved more cautiously during nighttime crossings (i.e., less likely to cross, longer crossing initiation time (CIT) when there was no eHMI). The lower perceived safety ratings were more prominent for older pedestrians, especially when crossing at 3-second time gaps and in the nighttime environment. eHMI decreased CIT for both age groups. However, different interpretations of eHMI were observed between younger and older pedestrians, showing that eHMI might have been used differently across age groups. Finally, an eHMI failure trial mainly affected younger pedestrians, whose collision rate increased from 0.43% in non-deceleration trials without eHMI, to 1.72% when the vehicle displayed the eHMI but did not decelerate. This study demonstrated that pedestrians are likely to behave differently during daytime and nighttime, and that older pedestrians are likely to have different requirements from AVs than younger pedestrians. This knowledge should inform the design of effective communication for AVs.