Congestion threshold is embedded in the congestion definition. Two basic approaches exist in current practice for setting the congestion threshold. One common approach uses the 'free-flow' or unimpeded conditions as the congestion threshold. Another approach uses target or 'acceptable' conditions. The limited research that has been conducted on the congestion threshold issue focuses on operational problems or policy debates, but relatively little investigation of the effect on decision-making for transportation investment and resource allocation. This research investigated the differences inherent in the threshold choices using detailed freeway data from seven metropolitan areas. Congestion performance measures of delay per mile, Travel Time Index and Planning Time Index were evaluated. This research specifically examined: 1) the ranking values of congestion measure for different congestion thresholds under a variety of real-world travel time distributions, 2) the relationship between change of congestion threshold and change of performance measure, and 3) the appropriateness of using speed limit as a congestion threshold choice by evaluating the peak and off-peak average speed changes in relation to a speed limit change in Houston, Texas.
Investigating the Effect of Freeway Congestion Thresholds on Decision-Making Inputs
2010
168 pages
Report
Keine Angabe
Englisch
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