Citation

Brilon W. Transp. Res. Circular 2000; (E-C018): 26-41.

Copyright

(Copyright © 2000, U.S. National Academy of Sciences Transportation Research Board)

DOI

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PMID

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Abstract

Traditional traffic engineering methodology is usually concentrated on one specific hourly traffic demand, q, which is then compared with the capacity, c, for the highway facility under consideration to estimate the expected traffic flow performance. To estimate demand, one or two hour-long periods are analyzed to represent the whole variety of potential traffic volumes. Generally conditions for the remaining 8,758 hours of the year are not observed or considered. In addition, the use of this brief period makes it difficult to estimate the overall economic loss resulting from traffic congestion. This traditional approach is expected to be enhanced in the future in two aspects. This wider view becomes possible due to improved information availability and enhanced data processing capabilities to be expected for the near future. Instead of considering demand, capacity, and quality of flow as three separate terms, the new term "efficiency" is introduced. The maximization of the "efficiency" usually reveals the optimum utilization of a traffic facility. This new term, "efficiency," has the potential to provide an objective parameter to distinguish between Level of Service (LOS) D and E for freeway facilities instead of using subjective assessment, as is currently done. Capacity and traffic demand can be treated as random variables. Moreover, demand can be estimated over the sequence of the hours of a whole year. The comparison of demand with capacity over the whole year will reveal the cumulative delay, which can be assessed in terms of economic losses. Thus a more complete picture of the consequences caused by different design decisions is available to the decision maker. Aspects of randomness, systematic capacity variation, incidents, and accidents can be included into the evaluation easily. These principles are illustrated for the application on two tunnel-related studies.