Guidelines for Using Late Merge Traffic Control in Work Zones

The late merge traffic control strategy has been proposed as a way to improve flow at work zone lane closures by maximizing queue storage space and creating more orderly merging. The late merge instructs drivers to use all lanes to the work zone taper and then take turns proceeding through the work zone. There is little information available on when the late merge should be used, however, and a limited understanding of the factors that influence its performance. This paper discusses the results of a simulation study of the late merge concept using microscopic traffic simulation. The late merge concept was evaluated by comparing it with traditional traffic control, through a full factorial analysis. Results of the computer simulations showed that the late merge produced a statistically significant increase in throughput volume versus the traditional merge for the three-to-one lane closure configuration across all combinations of analysis factors. Although the two-to-one and three-to-two configurations did not show significant improvement in throughput overall, it was found that as the percentage of heavy vehicles increased, the late merge did foster higher throughput volumes than traditional traffic control. The results of the simulations indicate that the late merge may not provide as much of a benefit as previous studies had indicated and that the area of application for the late merge may be limited to situations where heavy vehicles constitute more than 20% of the traffic stream.