High- and Low-Order Overtaking-Ability Affordances

Objective: The aim of this study was to answer the question, Do drivers take into account the action boundaries of their car when overtaking? Background: The Morice et al. affordance-based approach to visually guided overtaking suggests that the “overtake-ability” affordance can be formalized as the ratio of the “minimum satisfying velocity” (MSV) of the maneuver to the maximum velocity (Vmax) of the driven car. In this definition, however, the maximum acceleration (Amax) of the vehicle is ignored. We hypothesize that drivers may be sensitive to an affordance redefined with the ratio of the “minimum satisfying acceleration” (MSA) to the Amax of the car. Method: Two groups of nine drivers drove cars differing in their Amax. They were instructed to attempt overtaking maneuvers in 25 situations resulting from the combination of five MSA and five MSV values. Results: When overtaking frequency was expressed as a function of MSV and MSA, maneuvers were found to be initiated differently for the two groups. However, when expressed as a function of MSV/Vmax and MSA/Amax, overtaking frequency was quite similar for both groups. Finally, a multiple regression coefficient analysis demonstrated that overtaking decisions are fully explained by a composite variable comprising MSA/Amax and the time required to reach MSV. Conclusion: Drivers reliably decide whether overtaking is safe (or not) by using low- and high-order variables taking into account their car’s maximum velocity and acceleration, respectively, as predicted by “affordance-based control” theory. Application: Potential applications include the design of overtaking assistance, which should exploit the MSA/Amax variables in order to suggest perceptually relevant overtaking solutions.