ATSSA Signal November December 2020

American Traffic Safety Services Association 26 Innovation ATSSA case studies address merging and special event issues Series includes six parts to be released during 2021 Convention ATSSA collaborated with roadway safety infrastructure industry profes- sionals to produce six new case studies this year. In this issue of The Signal , we look at case studies 5 and 6: • Work Zone Closure Merging Strategies • South by Southwest Planned Special Event The first two case studies were featured in the July/August issue of The Signal . The second two appeared in the September/ October issue. The six case studies will be combined into one case study booklet and officially released as part of ATSSA’s 51st Annual Convention & Traffic Expo scheduled as a virtual event for Feb. 8–12 and Feb. 16–18. (See details at Expo.ATSSA.com .) Case study booklets are amember bene- fit and available for digital download at ATSSA.com/Case-Studies. Hard copies are also available for purchase on the ATSSAwebsite. Booklets are available to non-members for a nominal fee and to members at discounted prices. Case Study 5: Work Zone Closure Merging Strategies Helping drivers to safelymerge at tempo- raryhighwaylaneclosuresandmaintaining asafeenvironment around theseclosures for both highway workers and drivers, is an ongoing challenge for departments of transportation (DOTs). Agenciesmust balance the needs of minimizing queue length at merge sites, managing speed variability, accounting for unanticipated driver behavior, and providing clear and simple communication to drivers. This case study examines several different approaches. Agencies including theMichigan Depart- ment of Transportation (MDOT) have improvedon the longstandingStatic Early Merge (which uses “Do Not Pass” signs to discourage aggressive maneuvers at the merge point, where some drivers merge late while others merge early) by making it more responsive to conditions in real time. ThisDynamicEarlyMergeapproachmakes theno-passing zonedynamic and respon- sive to changing traffic volumes, using multiple trailers spaced evenly along the approach to thework zone, with sensors that measure volume, speed, and lane occupancy at each location. The “DoNot PassWhen Flashing” signs activatewhen traffic volumes reach a pre-determined level, smoothing the flow of traffic as conditions change. The Static LateMerge, also known as the “zippermerge,” takes adifferent approach. It encourages drivers to use both lanes right up to the merge point, then take turns at themerging taper. This approach, currently in use in Michigan, Minnesota, andVirginia, represents adeparture from the typical driver behavior tomerge early, and requires clear signage urging driv- ers to use both lanes to themerge point. Some agencies have developed a fully dynamicapproachthat combines theearly and latemerging systems, and switches between the two based on traffic condi - tions. Using this DynamicMerge system, departmentsusesensorsandchangeable signage to deploy an early merge strat- egy when volumes are lighter, and a late merge strategywhenvolumes are sohigh that queues would exceed policy limits. The LouisianaDepartment of Transporta- tion and Development (LADOTD) devel- oped a Joint Merge strategy that creates a two-sided taper that removes the open lane priority. Researchers determined that this strategy increasedmerging effi - ciencybyminimizingqueues andallowing drivers to use all of the available storage space in both lanes. Researchers found lower speeds at locations approaching the taper, fewer lane changes, andmore evenlydistributedtrafficacrossboth lanes. In addition to managing driver behav- ior at the merge, agencies including the The pickup and dropoff location for the Austin, Texas, event shows the designated location, which was indicat- ed by 42-Inch Cones. (Photo courtesy of the City of Austin, Texas.)