Travel time estimation is of increasing importance to travelers and transportation professionals alike as congestion worsens in major urban areas. In fact, the reliability of travel time estimates on a given corridor may be more important for travelers, shippers, and transport managers than the travel time itself. This paper examines the uses of measured travel time reliability indices for improving real-time transportation management and traveler information using archived ITS data. Beginning with a literature review of travel time reliability and its value as a congestion measure, a content analysis of twenty regional transportation plans from across the nation is then described. Results from the content analysis indicate that travel time reliability is not currently used as a congestion measure, and that the most common measures of congestion were the volume-to-capacity ratio, vehicle hours of delay, and average speed. Then, as a case study using data from Portland, Oregon, several reliability measures are tested including travel time, 95th percentile travel time, travel time index, buffer index, planning time index, and congestion frequency. The buffer index is used to prioritize freeway corridors according to travel time reliability. Metropolitan planning organizations should use travel time reliability in the following ways: 1) incorporate it as a system-wide goal; 2) evaluate roadway segments according to travel time reliability measures; and 3) prioritize roadway segments using those measures.
Samenvatting