Driver perception hypothesis: Driving simulator study

• The driver perception hypothesis was tested using an interactive driving simulator.
• For crest combinations the speeds were fully consistent with the perception hypothesis.
• The perception hypothesis on sag combinations was not supported.
• The effects of the combined curves did not change in function of the level of the radius.

According the driver perception hypothesis, horizontal curves appear sharper or flatter when overlapping with crest or sag vertical curves, respectively. Confirmations of this hypothesis are provided by studies carried out using non-interactive techniques that do not allow the analysis of the driver’s reactions to the visual perception of the road.This study was aimed to add to the body of knowledge concerning driver’s speed behavior on combined curves, as well as to test the perception hypothesis based on the speed data collected during tests in the interactive CRISS driving simulator.Speeds on the tangent-curve transition of crest and sag combinations were compared to those on the tangent-curve transition of horizontal curves with the same radii but on a flat grade (reference curves).For the crest combinations the results of the statistical analyses were fully consistent with the perception hypothesis. On the sag combinations, on the contrary, the driver’s speed behavior did not differ in any statistically significant way from that on the reference curves. Therefore this finding did not support the perception hypothesis on the sag combinations. The effects of the combined curves on the driver’s speed behavior did not change in function of the level of the radius. Some implications of these findings have been highlighted.