Minimum Lengths of Acceleration Lanes Based on Actual Driver Behavior and Vehicle Capabilities

Abstract

The current geometric design guide in the US uses design values for the required lengths of acceleration lanes that are based on research studies conducted more than 50 years ago. Those design values need to be updated to reflect current drivers’ behavior patterns and vehicle mechanical characteristics. This paper presents a new method for determining the required lengths of acceleration lanes at freeway interchanges based on actual driver behavior and vehicle acceleration capabilities. Realistic acceleration profiles were established for different drivers accelerating from the design speed of the entrance ramp to that of the highway into which they are merging. The acceleration profiles were established based on field data collected using Global Positioning System (GPS) data-logging devices that recorded the positions and the instantaneous speeds of different vehicle types piloted by different drivers at 1-s intervals. Design tables were developed for different grades to help designers select the required length of the acceleration lane based on the design speeds of the freeway and the entrance ramp. The developed design tables have the potential to provide design values for the lengths of acceleration lanes that are more realistic and representative of current vehicle and driver characteristics.