Safety evaluation of road alignment based on energy conservation law

In order to estimate the influences of horizontal and vertical alignments on the safety of high classified highway in mountain area, based on energy conservation law, the influences of longitudinal gradient, gradient length and horizontal curve radius on the temperature rise of brake system were analyzed when vehicle ran downhill.Taking example for a downhill section in mountain area, the relationship between highway alignments and accident rates was validated.Analysis result indicates that when vehicle runs stably the critical gradient increases with the increases of transmission ratio and vehicle speed.Highway safety decreases with the increase of the product between average gradient and gradient length.Because the lesser curve radius can enhance the ability of engine brake, highway safety is improved.The larger mean square error of curve radius may increase the use frequency of vehicle brake, therefore, highway safety will be reduced.