Spacing and geometric design indexes of auxiliary lanes on two-lane highway in China

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.