Investigation of Freeway Capacity: (A) Effect of Auxiliary Lanes on Freeway Segment Volume Throughput and (B) Freeway Segment Capacity Estimation for Florida Freeways

摘要

Auxiliary lanes are generally used to reduce the traffic turbulence created by merging and diverging movements and are primarily used by vehicles either entering or exiting the freeway. The Highway Capacity Manual (HCM) does not offer explicit guidance on the benefit of adding an auxiliary lane between an on- and off-ramp. The objective of this part of the project was to quantify the additional traffic volume that can be accommodated on a freeway segment by connecting an on-ramp to an off-ramp with an auxiliary lane. The approach used was to identify the traffic volume level at which each level of service density threshold was met for the conditions of with and without an auxiliary lane. The OCRSIM simulation program was used to generate the data upon which to establish the quantitative effect of an auxiliary lane. Two versions of an adjustment equation that gives the percentage increase in volume throughput due to adding an auxiliary lane were developed. The developed equations are simply a function of the number of mainline lanes, as other factors were not found to significantly affect the percentage increase in volume throughput. The capacity of a freeway segment is a critical factor for the assessment of the traffic flow operations on freeway facilities.