Contrasting Time-Based and Distance-Based Measures for Quantifying Traffic Congestion Levels: Analysis of New Jersey Counties

Various approaches for quantifying congestion and how these different measures affect the perception of the problem are discussed. In a study done for the state of New Jersey, thresholds of the volume-capacity ratio on any given roadway were adopted to identify where congestion was occurring. The severity of this congestion was then analyzed by using both distance-based and time-based measures to describe the magnitude of the problems. It was found that the distance-based measures such as vehicle kilometers of travel indicated a relatively small amount of congestion to be present statewide. Time-based measures such as vehicle hours of travel in congestion revealed more severe problems, with more than half of total peak period travel time in many counties being spent in congested conditions. The time-based measures of congestion provided a stronger basis for more generalized conclusions. These measures indicated that much of the delay due to congestion in New Jersey could be attributed to the most severely congested locations in the state. These same time-based measures also strongly suggested that arterial roadways contribute far more to the overall congestion problem than previously reported. Time-based congestion measures provide a different perception on congestion, one in keeping with the common perception of the problem. Time-based congestion measures also provide stronger guidance on identifying major issues, enabling policy makers to better address problems within the state and solutions that are most likely to have the greatest impact.