Traffic Flow Characteristics of the Late Merge Work Zone Control Strategy

Conventional traffic control plans such as the one used in Nebraska (NDOR Merge) for lane closures of rural Interstate highways normally work well as long as congestion does not develop. However, when the traffic demand exceeds the capacity of the work zone, queues may extend back past the advance warning signs, often surprising approaching traffic and increasing the accident potential. The Late Merge is a merge-control concept developed by the Pennsylvania Department of Transportation to reduce the length of queues and reduce the road rage that often develops among drivers. The operational effects of the Late Merge were evaluated. The traffic flow characteristics determined from the field data indicate that the Late Merge is more effective than the NDOR Merge in terms of the safety and efficiency of merging operations in advance of lane closures on Interstate highways. The Late Merge has higher capacity and results in fewer traffic conflicts. However, it was also found that the concept might not be working as effectively as it is capable of. Based on the lane distribution data obtained during both free-flow and congested-flow periods, it can be concluded that some motorists did not follow the directions given by the traffic control signs, thus reducing the effectiveness of the merging operation. The potential benefits of the Late Merge will not be fully realized until drivers, particularly truck drivers, gain a better understanding and acceptance of the concept.