vehicles. However, the operation of the transition zone changes as volume conditions change from a low to high level of traffic. In low- to medium-volume conditions, merge transition areas operate with few problems since there are numerous gaps of adequate size to per- mit drivers to change lanes. Often, drivers in the continuing lane adjust their speed to create gap opportunities for merging drivers, similar to freeway on-ramps. However, once traffic demand reaches or exceeds the capacity of the transition area, speeds rapidly drop and queues begin to form as motorists begin competing for suitable gap opportunities into the continuing lane(s). Under these conditions queues can rapidly extend upstream for long distances from the merge point, and driver frustrations grow as conflicts between vehicles approaching the merge point arise. Part of the driver frustration may be attributed to early merging. Past study suggests that many drivers tend to merge “early” at dis- tances significantly in advance of the merge point because of the use of advanced warning signs that communicate which lane is about to be closed ahead and how much further it is to the closure (1). Early merging creates an imbalance in lane volume on the road segment ahead of the merge point. A high concentration of vehicles in the “open” lane leads to a longer overall queue length and can also cre- ate disparities in operating speeds between the open and “closed” lanes. Differential speeds have been recognized to be related to increased crash frequency (2). From a driver behavioral standpoint, some aggressive drivers take advantage of the imbalanced conditions to pass slower or stopped traffic for as long as possible, even proceeding to the very front of the queue before merging into the open lane. This creates irritation among early mergers who have “waited their turn” instead of mov- ing to the very front of the queue and merging into an insufficient gap. On occasion some drivers have combated these conditions by resorting to partially or even fully blocking the closed lane to pre- vent late merging drivers from passing. Similar behaviors have also been exhibited by truck drivers who create “rolling blockades” that prevent any passing beyond their location (3). In the past, these con- ditions have even led to dangerous maneuvers such as driving on shoulders, incidents of road rage, and in some locations even fatal traffic crashes (4). POTENTIAL SOLUTION In an effort to improve many of the negative conditions described above, a novel and innovative technique has been suggested. The method, known as the “joint merge,” operates by encouraging approaching drivers to evenly balance their lane positions upstream of the transition zone by not specifying the lane that will terminate Joint Merge and Its Impact on Merging Speeds in Lane Reduction Areas of Construction Zone Wakeel I. A. Idewu and Brian Wolshon 31 To increase the efficiency and safety of traffic flow in the vicinity of lane reduction transition areas, engineers have begun to use innova- tive 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 facil- itates 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 driv- ers 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. Maintaining safety and mobility in locations where lane reductions are required is a constant concern for highway agencies and a frequent frustration for drivers. Lane reduction transition areas are locations where traffic from a travel lane that is terminating is required to merge into an adjacent continuing lane. Such terminations are necessary in advance of construction work zones that require temporary lane closures in one or more lanes. The design of these transitions is based on a lengthy history of observation and experience and incor- porates tapers with sufficient length to permit safe and efficient vehicle merging. Lane reduction transition areas are also accompa- nied by signs that provide advanced warning of the impending lane termination. For temporary lane closures, such as those used in work zones, additional control devices, such as flashing arrow boards and barricades, are also used. Since lane closures reduce capacity, traffic control devices and merging strategies play an important role in managing the flow of W. I. A. Idewu, Department of Civil and Environmental Engineering, Virginia Military Institute, 610 Nichols Hall, Lexington, VA 24450. B. Wolshon, Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803-6405. Corresponding author: W. I. A. Idewu, idewuw@vmi.edu. Transportation Research Record: Journal of the Transportation Research Board, No. 2169, Transportation Research Board of the National Academies, Washington, D.C., 2010, pp. 31–39. DOI: 10.3141/2169-04