Length of Acceleration and Deceleration Lane on Urban Expressway

To ensure traffic flow on urban expressway running safely and efficiently and perfect the designing standard of interchange spacing, it is necessary to study the length of acceleration and deceleration lane on urban expressway. Based on the vehicles' running characteristics, the acceleration lane was divided into three sections, namely acceleration section, waiting merging section and width transition section. Applying dynamics theory, the models calculating the length of acceleration section and width transition section were got. By combining probability theory and differential method and taking main lane traffic volume into consideration, the model calculating the length of waiting merging section was established as well. Then, the twice deceleration theory put forward by AASHTO(American Association of State Highway and Transportation Officials) was adopted to analyze the vehicles' running process on deceleration lane. The deceleration lane was divided into three sections, too, i.e. width transition section, the first and second deceleration section. Applying the dynamics theory again, the model calculating the length of width transition section was got. Applying dynamics theory and taking drivers' driving comfort into consideration, the models calculating the length of the first and second deceleration section were established as well. And then, taking mainline lane vehicles' time headway distribution and mainline lane and ramp vehicles' velocity combination into consideration, the length values of acceleration and deceleration lane on urban expressway were calculated. The calculation results indicate that the length of acceleration and deceleration lane increases with the increase of mainline lane vehicles' velocity and decreases with the increase of ramp vehicles' velocity.