Development and operational analysis of highway alternating merge transition zones

The design and control of work zone traffic control areas is governed by standards published by the United States Department of Transportation (US-DOT) and documented in the Manual for Uniform Control Devices (MUTCD). While these configurations have evolved over time to reflect safer and more efficient management practices and have become familiar to drivers, they are also recognized as areas of vehicle conflict that can cause congestion and safety problems. As part of this research, a new design has been developed that has the potential to lessen the detrimental effects of lane closures in work zones. This new concept, known as the “joint merge,” is configured to simultaneously merge two lanes into one. The key feature of the joint merge design is its use of a two-sided taper. In it, both lanes approaching a lane reduction are simultaneously tapered into a single lane, with neither lane having a priority, thereby influencing drivers to merge in a smooth alternating pattern. The joint merge configuration was examined at a work zone site in Louisiana and compared to the MUTCD conventional merge configuration that was tested at the same site. The performance measures collected in the field included lane-specific volume and vehicle speeds. The two designs were quantitatively compared using Analysis of Variance (ANOVA) and T-test statistical procedures. These two testing agents were used to analyze the effects each design had on volume, speed and vehicle lane distributions at several locations in advance of the work zone entrance. Using speed and volume data, the joint merge traffic control plan was found to increase the efficiency of the closed lane and better encourage the use of both lanes leading up to the work zone entrance. It was further concluded that the number of lane changes during low and high volume periods decreased when the joint merge configuration was used. While no conclusive findings could be made relative to its specific effect on capacity, the video recordings and lane usage data suggested that the joint merge strategy was understood and well received by most drivers.