Temporary Losses of Highway Capacity and Impacts on Performance: Phase 2

Chin, Shih-Miao · 2004 · OpenAlex-citations

DOI: 10.2172/885576

archive: archived pipeline: cataloged verified

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Summary

This report presents the findings of the Temporary Loss of Capacity (TLC) study, Phase 2 (TLC2), conducted by Oak Ridge National Laboratory for the Federal Highway Administration. The research addresses the significant economic and quality-of-life impacts caused by traffic congestion and temporary capacity-reducing events on the U.S. highway system. While the initial TLC study provided nationwide estimates for crashes, breakdowns, weather, and signal timing, TLC2 expands the scope to include rain, toll collection facilities, railroad crossings, and commercial truck pickup and delivery (PUD) activities. It also refines estimates for work zones and adverse weather conditions like fog and snow, while correcting computational errors from the first phase. The study focuses on urban and rural freeways and principal arterials, which accounted for approximately 54 percent of total vehicle-miles of travel (VMT) in 1999. The methodology involves estimating capacity reductions and resulting delays for specific event types across the national highway network. For crashes and breakdowns, the study assigns events to specific network locations and estimates lane closures and duration to calculate delay. Work zone impacts are derived from data on lane closures and reduced lane capacities. Adverse weather effects are mapped to highway segments using National Weather Service data and speed-capacity adjustment factors. Sub-optimal signal timing, railroad crossings, toll facilities, and PUD activities are analyzed using specific delay assumptions and transaction rates. The study aggregates these individual estimates to provide a composite picture of delay, categorized by area type, highway type, and time of day. The results indicate that non-fatal crashes and work zones are the dominant sources of delay, accounting for over two-thirds of the total delay attributed to temporary capacity losses. Most weather-related capacity reduction occurred due to rain on urban and rural arterials, while fog and snow impacts were significantly lower in TLC2 than in the initial study. Sub-optimal signal timing caused the greatest delay in very large urban areas, primarily during off-peak periods. Nearly 90 percent of delay from PUD activities occurred in very large urban areas, and over three-quarters of toll facility delay occurred in lanes using non-electronic collection methods. When normalized by travel volume, medium-sized urban areas experienced the least delay per thousand miles of travel. The study also found that most delay from TLC events occurred during off-peak periods, though on a per-mile basis, delay was more prevalent during peak periods on congested roadways. The significance of this work lies in providing the first comprehensive, nationwide estimates of delay caused by specific temporary capacity-reducing events. By quantifying these impacts, the study offers vital data for formulating public policies regarding highway infrastructure and operations. The findings highlight the disproportionate impact of crashes and work zones, suggesting that strategies to mitigate these events could yield significant improvements in system reliability and mobility. The report concludes by outlining next steps, including estimating impacts from simultaneous events, conducting sensitivity analyses, and assessing the potential impacts of new policies and technologies on these delay sources.

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• work zones