Urban Freeway Congestion: Quantification of the Problem and Effectiveness of Potential Solutions

Urban congestion is a serious and worsening national problem, one which is receiving increasing attention from transportation engineers, planners, and researchers, as well as other local, state, and national officials. Urban freeways, which carry nearly 30’% of all traffic in urban areas, are particularly affected by growing urban congestion. In 1983, about 557. of urban freeway travel during the peak hour occurred under congested conditions, according to a U.S. Department of Transportation report.’ This figure is up from 41% in 1975, and it iS expected to increase even further as urban freeway volumes continue to increase. One of the difficulties in examining the problem of urban traffic congestion and its potential solutions is that no detailed quantification of either the size of the problem or its projected future growth has been available. As a result, the relative effectiveness of various types of solutions to the problem cannot be described. The Traffic Systems Division of the Federal Highway Administration’s Off ice of Research, Development, and Technology has focused on urban traffic congestion as not only an immediate problem, but also the most serious longterm traffic research problem facing the United States. This paper is a result of a major staff research study of traffic congestion on urban freeways. A firstorder priority of the study was to undertake an analysis of the problem. The Highway Performance Monitoring System (HPMS) was chosen as the basic source of data for this study. The HPMS data base is maintained and updated annually by the Federal Highway Administration and consists of detailed geometric, traffic, and other data for a representative sample of roadway sections throughout the United States. The urban freeway sections of the HPMS data base are based on a sampling of approximately 507. and can be used to represent the total highway system through the use of state-supplied expansion factors. The data used in this study were for 1984 and were limited to freeways in urban areas with populations greater than 50,000. This data set consisted of 8,036 sample sections representing 15,335 miles of urban freeway. The 1984 data were entered into a microcomputer for computation of travel and congestion statistics; predictions of future urban freeway congestion statistics were calculated using state-supplied estimates of annual average daily traffic for each sample section in 2005 [see “Methodology” sidebar].