Zipper merge refers to a convention for merging traffic into a reduced number of lanes, where drivers use both lanes to advance to the lane reduction point and merge at that location, alternating turns. In a dynamic zipper merge system, the technique switches between the zipper and conventional early merge depending on the traffic condition since the zipper merge does not work well when the demand is low.
The North Carolina Department of Transportation implemented the dynamic zipper merge system for several work zones in the past several years. Congruent with the outcomes from past case studies, NCDOT found evidence of its operational and safety benefits over the conventional early merge. However, because the technique comes with vast installation and maintenance cost, the significance of its benefits relative to the low-cost early merge needs to be known. Previous studies showed that the statistical significance of the difference in the performance using either technique was either not apparent or mixed across different metrics. Moreover, the transferability of the benefits across different demand levels is still unknown, likely because of the lack of observational data and the complexity of simulating the merging process. Also, the best practices of the device configurations of dynamic zipper merge for various lane closures are not well documented, underscoring the need for an investigation in this regard.
The research team will address these questions by collecting and analyzing data from both previous and current applications of dynamic and early merge techniques. This effort will encompass collecting data on identifying best practices of device configurations of the dynamic zipper merge for different lane closures, collecting traffic operation and safety data associated with dynamic and early merges, determining the statistical significance of the difference in their performance, and assessing the feasibility of the dynamic zipper merge for day-time lane closures. With the outcomes of this research, NCDOT can make more informed decisions on implementing this technique while potentially expanding the scope of dynamic zipper merge beyond the current practice.
