Natural Diversion at Temporary Work Zone Lane Closures on Urban Freeways in Texas

The report documents the results of eleven field studies at temporary work zone lane closures on urban freeways in Texas. Study results indicated a large amount of natural diversion occurred at those sites where normal freeway traffic demands far exceed the available capacity through the work zone. Entrance ramp volumes were lower a considerable distance upstream of the beginning of the queue, and were even lower at ramps located within the actual freeway queuing. Exit ramps upstream of the queue displayed very small changes in volumes. In contrast, the first exit ramp motorists encountered after reaching the freeway queue consistently experienced significant increases in volumes. As a result of the significant diversion occurring at each site, freeway queuing and delays tended to reach a threshold soon after the lane closure was enacted. The queue and delay then remained at approximately that threshold level throughout the duration of the closure. Also discussed in the report is the application of the findings from these studies to the QUEWZ computer model for estimating queuing and road user costs at freeway lane closures.