Joint Merge and Its Impact on Merging Speeds in Lane Reduction Areas of Construction Zone

To increase the efficiency and safety of traffic flow in the vicinity of lane reduction transition areas, engineers have begun to use innovative techniques to facilitate traffic flow through these bottleneck areas. One technique, alternating merging, encourages drivers to take turns when merging in freeway lanes and ramps. This paper discusses the development of the joint merge, a new traffic control design that facilitates alternating merge patterns, along with the results of a field experiment to examine its effects on traffic flow. The key feature of the joint merge design is its two-sided taper in which both approach lanes are reduced simultaneously into a single lane, thereby eliminating an assigned lane priority. To evaluate its effect on traffic, a field study was conducted in which a joint merge configuration was erected in a live, work intensity–controlled work zone in Louisiana. Lane-specific volume and vehicle speeds in the joint merge were compared with those observed in a conventional merge design at the same site. Overall, merging speeds were found to be relatively similar at volumes ranging from 600 to 1,200 vehicles per hour and did not affect the discharge rate at the merge outflow point. However, the experimental results did suggest that drivers were more cautious in their merging maneuvers. This was thought to be attributable to the joint merge, which produced a more evenly balanced lane volume at the transition zone entrance.