Study on The Safety Length of Acceleration and Deceleration Lane of Left-Side Ramp on Freeway

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Jin Zhou
Jing Fang
Rong-gui Zhou

Acceleration and deceleration lanes are the critical parts which ensure safety maneuver between main lane and ramp. Due to terrain constraints, the left exit or left entry ramp used in the interchange design doesn’t accord with the right-hand driving habits and drivers’ expectations. To ensure the safety and efficiency of the operation, it’s necessary to study the safety length of the acceleration and deceleration lanes on left-side ramp considering the vehicles’ operating characteristic of merging or diverging. According to the headway distribution of main lane in merging area, the probability model of vehicles in the acceleration lane merged into the main lane was established based on the acceptance gap theory. The length of the acceleration lane can be calculated under the different operating speed and merging probabilities. Based on Secondary reduction theory, the required safety length of deceleration lane driving from the inner lane to the left-side exit ramp was determined to ensure that those diverging vehicles do not affect the operation of the vehicles on the main lanes. The recommended length of acceleration and deceleration lane will provide a technical sustain to the safety design of interchange.

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