Quantification of Quality and Efficiency of Human Gaze Strategies Using the Example of Interactions between Motorists and Vulnerable Road Users

Abstract

In urban traffic, collisions between motorized vehicles and Vulnerable Road Users (VRUs) have severe consequences, but are fortunately rare. Their infrequent occurrence on average (compared with far more common individual perceptual and behavioral errors by both drivers and VRUs) reflects an underlying fault tolerance in traffic processes. However, the degree of fault tolerance varies among traffic situations. The underlying perceptual and cognitive processes involved are complex and can require a high level of attention and concentration, particularly in situations with intersecting trajectories. These processes can occasionally fail, leading to collision risk. The situation of right-turning motorists (in right-hand-drive countries) encountering cyclists moving straight on a bike lane (with right of way) has a particularly low error tolerance, since motorists must actively scan for cyclists approaching from behind. In order to develop, test and assess solutions that mitigate collision risk in this situation, the behavior-related causation mechanisms need investigation. This is the focus of this article. We conducted a trial on our closed test track with n~=~35 subjects. The experiment was designed as an within-subject design with three independent factors: maneuver, velocity and cognitive load in a n-back task. The trial included observations of participants' gaze control. Within the present article, we study the experimental evidence on gaze behavior of participants. A primary research focus was the quality and efficiency of the safeguarding gaze behavior of participants in order to draw conclusions on the causation mechanisms of collisions in this situation. For this purpose we define metrics in order to quantify the quality and efficiency of a specific gaze behavior. Interestingly, only four of 35 participants reached a collision risk of 0\% relating to the defined quality metric. Furthermore, we identified four distinct gaze strategy groups through hierarchical clustering, where one group performed particularly few glances overall. This group showed significant differences with respect to the defined quality metric whereas the other groups showed only slight differences to each other. The results have implications on subsequent crash causation model development.

Keywords: driver behavior, Human Experimental Psychology, Risk Taking, Vision, Vulnerable Transport User