Optimization on Design Parameters of Road Longitudinal Slope Based on Truck Dynamics

In recent years, with major cities turning to the stock development stage, the development and construction of underground space has gradually become an important strategy for sustainable urban development. The construction of underground passages at freight transport hubs will help the separation of passenger and cargo, which will greatly alleviate urban traffic jam and improve transport efficiency. However, due to the restriction on urban land use and construction cost, it is difficult to achieve gentle slope design for all of underground passages, longitudinal slopes with large gradient are unavoidable. Generally, trucks have quite large gross weight, its uphill speed reduction and downhill brake disc temperature rise would affect road capacity and traffic safety greatly. Therefore, it is quite necessary to propose optimal design of longitudinal slopes given the consideration of truck dynamic performance and its driving safety. Truck models were established in TruckSim, they were used to simulate vehicle driving status uphill and downhill then. Speed reduction and brake disc temperature rise were used to obtain suitable slope gradient and length based on simulation. It was concluded that slope gradient and vehicle output power ratio have great influence on truck climbing ability. Using speed reduction of 20 km/h between vehicle uphill original speed and its stable uphill speed for reference, the maximum slope length for uphill with different gradient could be obtained. Slope gradient and vehicle gross weight have giant impact on brake disc temperature rise. Using brake disc temperature of 200 and 260 °C for reference, suitable slope length for downhill with different gradient were obtained.