Traffic congestion continues to grow on the nation’s highways, which is increasing the concerns of transportation agencies, the business community, and the general public. Congestion includes recurring and nonrecurring components. Recurring congestion reflects routine day-to-day delays during specific time periods where traffic demand exceeds available roadway capacity. Road users have come to expect these daily traffic patterns and adjust their travel plans accordingly to achieve timely arrivals. Nonrecurring congestion that causes unexpected extra delays results from random incidents, such as crashes, weather, and work zones. Road users are frustrated by these unexpected delays that can make for unreliable arrival times at their destinations. The SHRP 2 Reliability research objective focuses on reducing nonrecurring congestion through incident reduction, management, response, and mitigation. Achieving this objective will improve travel time reliability for both people and freight. Highway geometric design, which involves the provision of physical elements and their dimensions, plays a major contributory role in the traffic operations conditions and safety performance results on highway facilities. Current design standards and guidance manuals do not address the use and effectiveness of design elements as an explicit countermeasure to prevent or mitigate the negative effects of nonrecurring factors and events that happen on a regular basis causing unreliable travel for highway users. This research seeks to better understand how different geometric design elements can contribute to more-reliable travel times and develop procedures that will allow agencies and professional practitioners to evaluate the cost-effectiveness of alternative design elements as a potential solution to specific nonrecurring conditions. The research team established a list of the physical design elements that could be used to influence nonrecurring congestion. Guidance based on published information and interviews with select transportation agencies is provided for each element. This guidance provides information on advantages and disadvantages, typical applications, expected benefits, factors to consider when selecting the treatment, design criteria, operational and safety effectiveness, and costs. In addition, analysis procedures and models were developed to provide the quantitative measurement of the operational effectiveness, safety effectiveness, and life-cycle cost—benefit results to estimate the potential impact of any candidate design element to improve travel time reliability and reduce nonrecurring congestion. This research has generated two companion products that allow transportation agencies and professionals to apply these research findings effectively in daily practice. These products are the Design Guide for Addressing Non-recurrent Congestion, which is a catalogue of the design elements and their associated use information, and the Analysis Tool for Design Treatments to Address Nonrecurring Congestion, which is a tool to execute the various analysis procedures and models to measure the effectiveness of a design element on travel time reliability. (Author/publisher)
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