Improving Transportation System Performance: Construction-Zone Capacity Bottleneck Example

Transportation engineers continually strive to improve transportation system performance. In many cases, these efforts focus on major changes such as new roads, improved design standards, better multimodal options, and the like. In some cases, significant performance improvement can result from small changes. I experienced an example of poor performance over the weekend after this year’s July 4th holiday, which I hope will be instructive.

Traveling north on Interstate 79 midafternoon on July 7, 2013 (the end of the July 4th holiday weekend) in West Virginia, traffic was heavy but moving along smoothly. However, I encountered a 7-km (4.5-mi), two-lane, very slow-moving queue of traffic. The slow-moving queue continued through a merge into one lane for a construction zone 5-km (3-mi) along the roadway. The construction zone encompassed two bridge deck replacement projects, with a 5-km (3-mi) intermediate stretch that included a relatively steep uphill grade. Trucks and light-duty vehicles towing trailers struggled with the uphill grade and climbed only slowly in the one lane available. This uphill grade was the capacity bottleneck for the traffic queue, as the traffic was free-flow immediately after the uphill even though still in the construction zone. The result was about a 40-min delay when I came through (and likely longer as the holiday traffic increased later in the day).

What could a transportation engineer do to improve this system performance? I should have taken advantage of real-time traffic information and plotted an alternative route. As a result, I would not have added to the congestion on I-79. For the construction-zone designer, the single-merge could have been separated into two merges with multiple lanes available in between the lanes. With that two-merge design, the steep uphill capacity bottleneck would have had two lanes. The cost of two merges rather than one merge is not large and the road users would have much lower travel costs. Interestingly, I passed a similar two-bridge deck project on I-79 earlier the same day with an identical construction-zone design. In this case, traffic was free-flowing since the middle section of the construction zone did not have a severe capacity constraint.

In this case, transportation professionals could have significantly improved system performance by encouraging active use of traveler-information systems and ensuring that construction-zone traffic designs are efficient and cost-effective. Design changes of this sort can have low costs but substantial benefits. I might add that there is no shortage of relevant literature on such strategies, both in the Journal and other sources. Over the past several years there have been many articles in the Journal related to these issues. My recent experience serves as a reminder that the real impact of the Journal is when researchers see their innovations, findings, and recommendations implemented. I would encourage all authors and readers of the Journal to look for opportunities to help accelerate adoption and implementation of material published in the Journal.