In order to strengthen the safety of highway roadsides, it is necessary to take targeted measures according to the roadside hazards, so there is an urgent need to develop research on risk evaluation of highway roadside accidents. Based on accident simulation analysis and the form of accident after vehicles run to the roadside, the rollover risk of roadside accident is classed into four grades, namely, no departure from the ground, slight departure from the ground, one or two turnovers, and more than two turnovers. The factors involved in the causes of roadside accidents of different rollover risks are studied, and the thresholds of driving speed, sideslope gradient, and sideslope height are given. A Bayesian network for risk evaluation of roadside accidents is constructed. Based on the factor thresholds for the causes of roadside accidents, the calculation methods of the probability of different rollover risks of roadside accidents are carried out according to a single factor, two factors, and three factors. The typical cases of roadside accidents are analyzed and the calculation results of the Bayesian network show that the probability of one or two turnover accidents is 0.939, which is consistent with the results of roadside accident simulation tests, proving the accuracy of the risk evaluation methods for highway roadside accidents.

Auxiliary lanes on two-lane highway are lanes setting on the right side of highway for the slow vehicles, and they can provide safe overtaking chances for cars using the original lane instead of the opposite lane. Based on the principle that the net benefit is greater than zero, the calculation model of the minimum spacing of auxiliary lanes on two-lane highway is established. After calibrating the model parameters, recommended minimum spacing values for auxiliary lanes are given corresponding to different highway classes, design speeds, and terrains. Based on traffic simulation data, the relationship model is established among the length of auxiliary lane section with uniform widths, traffic volumes, and driving speeds. By analyzing the design capacity of two-lane highway, suggestion values of the length of auxiliary lane section with uniform widths are given for two-lane highway with different design speeds and terrains. Based on driving safety and questionnaire survey on lateral vehicle spaces, calculation formula and suggestion values are presented for the width of auxiliary lanes on two-lane highway.