The Key Parameter of Highway Longitudinal Grade Design

The limitation of the longitudinal grade length is dependent primarily on the climbing performance curves of a representative truck which is used in designing the longitudinal grade, taking into account of the initial speed at the entry to the grade and the allowed speed difference. Truck power-to-weight ratio is the basic choice for a representative truck used in designing the longitudinal gradient. Through analyzing the operating characteristics of passenger cars and trucks on upgrades which are more than 3 percent and 3 percent or less separately, the computation model of power-to-weight ratios can be inferred from the equation of motion when a truck is moving on upgrades, and a set of experiment approach is proposed to compute power-to-weight ratios. Studies show that there is an obvious speed influence of the longitudinal grade on the truck when the gradient is more than 3 percent, and that the power-to-weight ratios of a representative truck are about 8.0 kw/t to 8.33 kw/t in the testing expressway. This method can be referred to determine the truck power-to-weight ratio in other province or regions in order to form the geometry design parameters of the maximum longitudinal gradient and critical length of grade.