Analysis and prediction of operating speed on horizontal curve combined with longitudinal slope for expressway

This paper analyzes the operating speed characteristics at horizontal curve combined with longitudinal slope and proposes prediction models for expressway, whose design speed is 100 km/h. The observed speeds and the time headways are obtained, and the free flow condition is determined based on the relationship between them. Under the free flow condition, the operating speed is obtained and the relationship between operating speed and geometric alignments as radius of horizontal curve and longitudinal slope are analyzed. Lastly, the regression model, the BP neural network model and the fuzzy logic model are proposed to predict the operating speed, and the prediction accuracy is analyzed. The study results show that: When the time headway is greater than 6 s, the traffic condition can be taken as free condition, which could be used to calculate operating speed; The operating speed of passenger cars are influenced significantly by radius of horizontal curve, whereas the operating speed of trucks are influenced by the gradient of upgrade; The proposed three operating speed prediction models have comparable predict capability.