Improved Techniques for Traffic Control for Freeways and Work Zones (0-5326-S)

Bottlenecks can occur at lane drops, freeway merges, exit- and entry ramps, and many other locations where there is a change in road characteristics. However, bottlenecks created by incidents and work zone lane closures, where relatively large speed variations and long queues can be expected, are particularly high-risk locations. A major safety concern associated with freeway bottlenecks is increased rear-end crash potential. According to a recent Texas Department of Transportation (TxDOT) study (1), rear-end type collisions comprise over half of all urban freeway crashes, and about one-third of work zone crashes. Depending on the speed differentials between queued and approaching traffic, rear-end collisions can be quite severe. However, many of them could be avoided by providing effective advance warning for vehicles approaching the end of slow or stopped queues. When freeway bottlenecks are caused by work zone lane closures, rear-end crash potential can also be reduced by effective merge control. Conventional work zone traffic control, that encourages early merge, works well in light traffic when congestion does not develop. However, at traffic volumes higher than capacity it may lead to excessive queues extending beyond the advance warning signs, thereby increasing the risk of rear-end crashes. Also, the early merge type control may lead to erratic maneuvers, and road rage among drivers under congested conditions. There are alternative merge controls, such as the Indiana Lane Merge and the Late Merge, but both have operational characteristics that limit their effectiveness under both congested and uncongested traffic flow conditions. A merge strategy that would perform well under both non-congested and congested traffic conditions is needed. This research will attempt to determine the most effective merge control for various traffic and roadway conditions, while providing effective warning messages to alert drivers of slow or stopped traffic ahead. It is envisioned that the Dynamic Late Merge system will be used for this purpose. The research will also determine and evaluate an effective advance warning strategy for off-ramp queue spillback. Findings of this research will provide TxDOT with standardized and tested messages/techniques that can be used to improve the effectiveness of traffic control on freeways/work zones, reduce traffic delays, and increase safety of the traveling public. The research team will expand on the "Selection Strategy Flowchart" which was developed in TxDOT Project 0-4413 (1), and will develop guidelines for the selection and appropriate use of alternative merge control strategies such as the Late Merge, and Dynamic Late Merge.