Demanded vs Assumed friction along horizontal curves: an on-the-road experimental investigation

Horizontal curves are identified as high-severity crash locations along different types of roads: driver deceleration and acceleration rates when approaching and departing horizontal curves play a key role in developing speed profiles. Drivers behaviour along curves is strictly related to the perception of the road geometry that, in turn, affects road safety. This paper addresses an in depthstudy on drivers behaviour along horizontal curves by monitoring vehicles speed through mobile devices equipped with a prototype mobile application. A sample of 35 participants was selected; overall 86 curves with different radius were investigated. Participants driving behavior was analyzed by deriving lateral accelerations from GPS data. In order to assess how driving experience can affect the perception of the road geometry, expert drivers were involved in the experiments. Results show that the accumulated driving experience allows to adequately calibrate speed choices when approaching unsafe curves, having a better road geometry perception. Conversely, some drivers tend to overestimate their driving abilities; this lack of safety cognition may lead to erroneous speed estimations and to an unsafe driving behaviour. Finally, this research shows that mobile devices (if adequately equipped and managed) may be used to enhance the awareness of drivers and promote traffic safety.