Length of Slope Determination with Heavy Duty Vehicles

Unreasonable slope length and grade combinations have increased the traffic accident frequency on long and steep slopes in China. This paper explores heavy-duty vehicle speed performance on slopes after force distribution analysis during uphill and downhill procedures. A speed gain model is developed with various power-to-weight ratios from 5 to 8 kw/t for uphill and downhill processes. Results show that on certain grades, higher power-to-weight ratio causes smaller speed reduction and longer equilibrium slope during uphill processes before finally reaching higher stable speed, whereas during downhill processes on certain grades, higher vehicle power-to-weight ratio causes dramatic vehicle speed increases and longer distances to reach stable operating speed. Critical upgrade and downgrade lengths are identified for speed gaps over 20 km/h between adjacent sections. These results are applied to set climbing and escape lanes to improve safety and provide smooth traffic operation in mountainous areas. Results also provide guidelines for roadway geometry design.