Longitudinal acceleration of vehicles on complex mountain roads

Longitudinal acceleration is an important parameter used to describe a vehicle's kinematic behaviour and driver behaviour. Existing research on this parameter mainly focuses on urban roads. In this study, operational data were collected from vehicles travelling on two-lane mountain roads with complex shapes under normal driving conditions. The longitudinal acceleration's relationship with and sensitivity to road geometry and driving speed were analysed. The results showed that the inflection points of the cumulative frequency profile of acceleration/deceleration were located between the 90th and 92nd percentiles. At the 85th percentile, the acceleration and deceleration rates were 0·60 and 0·85 m/s², respectively. Additionally, the probability distribution curves for acceleration and deceleration were both positively skewed, and the peak values of the curves were 0·17 and 0·25 m/s², respectively. Furthermore, as the curve radius increased, the acceleration and deceleration rates decreased, and as the curve deflection angle increased, the acceleration and deceleration rates increased. The critical radius at which a driver would no longer decelerate while negotiating a curve was 275 m for the observed driving behaviour. Finally, as the driving speed increased, the acceleration rate decreased and finally became zero when the driving speed reached 90 km/h.