Operational Impacts of Auxiliary Lanes at Freeway Weaving Segments

A two-part study was conducted to assess the operational impacts of auxiliary lanes at freeway weaving segments. The first part of the study evaluated the improvements in traffic density and level of service at freeway segments before and after the addition of an auxiliary lane. The second part of the study developed recommendations on when to add auxiliary lanes at these freeway segments. The analyses were performed with the 2010 Edition of the Highway Capacity Software, which follows the procedure prescribed in Chapter 12 and 13 of the 2010 Edition of the Highway Capacity Manual. The 2010 Edition of the Highway Capacity Software was validated with field data collected at three freeway weaving segments in El Paso, Texas, prior to the analysis. The results show that adding an auxiliary lane at a freeway segment between on-ramp and off-ramp junctions reduces the traffic density in a range from 1.6 to 19.5 pc/mi/ln, or 4% to 50%, with the level service stays the same or improved. Higher improvements are obtained with shorter segment lengths combined with higher weaving volumes. This research has also developed charts which contain recommendations on when to include auxiliary lanes under different combinations of freeway volume, weaving volume and distance between the on-ramp and off-ramp.