You’re driving on the highway, enter a work zone, and see an upcoming lane closure. What do you do? Do you merge right away? Do you wait until the last minute? This familiar headache often backs up traffic and causes tempers to flare. One approach many agencies use is the “zipper merge,” which asks drivers to use both lanes until a marked merge area, then take turns merging. This idea can smooth traffic flow compared with everyone merging early, but in the real world it doesn’t always go as planned because drivers may be unfamiliar with the zipper merge concept. Would more, easy-to-read electronic signage help drivers follow the intended zipper merge approach?
Researchers Gagan Gupta, Nischal Gupta, Matin Mohammadpour, Peter T. Savolainen, Timothy J. Gates, Surya S. C. Congress, and Yazmin Dasgar sought to assess driver merging and lane utilization behavior under zipper merge lane control in single-lane closures on two-lane freeways. In their study, “Driver Merging and Lane Utilization Behavior under Zipper Merge Lane Control,” the authors tested how portable changeable message signs affect whether people continue to use the soon-to-close lane, and compared different sign setups (standard static zipper merge signs alone versus adding one electronic sign farther upstream or both one electronic sign farther upstream and one close to the merge point). Then they watched real traffic at multiple freeway work zones and measured how many drivers stayed in the closing lane at different distances from the merge. The team considered additional factors such as how busy the road was and how many trucks were in the mix. The results offer practical, real-world insight into where electronic messaging could be most effective. Learn more about this study and what it means for different traffic situations, in the Journal of Transportation Engineering, Part A: Systems at https://ascelibrary.org/doi/10.1061/JTEPBS.TEENG-9273. The abstract is below.
Abstract
Work zone lane closures require drivers to determine when and where to merge from a lane that is about to close to an adjacent open lane. The “zipper merge” strategy encourages drivers to stay in their lanes until reaching a defined merge area, where drivers alternate merging, analogous to a zipper. The zipper merge has been shown to provide better operational performance than the standard “early merge” scenario, reducing congestion and speed differentials between lanes. However, there is considerable variability in driver familiarity and behavior when encountering a zipper merge. To that end, this study evaluated the impacts of using supplemental portable changeable message signs (PCMS) to encourage drivers to follow the zipper merge strategy. Driver behavior was assessed through a series of field studies that compared vehicle lane utilization and merging behavior. The utilization rate of the soon-to-close lane was evaluated under three scenarios, which included (1) standard static zipper merge signage; (2) static signage with a PCMS displaying “USE BOTH LANES DURING BACKUP” upstream of the merge area; and (3) standard signage with two PCMS, with the second (downstream) sign displaying “MERGE HERE/TAKE TURNS” close to the start of the taper. A regression model was estimated to further investigate lane utilization while accounting for the effects of traffic volume, density, and the presence of heavy vehicles in the open and soon-to-close lanes. Installing an upstream PCMS improved lane utilization compared to static signs alone; however, the additional PCMS closer to the taper showed negligible impacts on lane utilization.
Learn more about how portable changeable message signs can influence zipper merge behavior in the ASCE Library: https://ascelibrary.org/doi/10.1061/JTEPBS.TEENG-9273.
