A New, Comprehensive, Congestion Measure for Freeways

The purpose of the study was to develop a new, objective measure to evaluate freeway congestion. Congestion has yet to be consistently defined and measured, Since, however, it has a big impact on decision-makers’ choices where and if to invest resources, its definition needs to be clarified, quantified and carefully studied. Therefore, this study also deals with the definition of congestion. A new measure, termed the Critical Occupancy Point (COP), is developed. Based on the known occupancy measure, COP evaluates the change in occupancy vs. speed and defines the point where congestion begins. COP may be developed from data taken from each freeway sensor separately because the information on each segment provides different measurements. It is shown that the COP measure is sensitive enough to identify recurrent and non-recurrent congestion and that it is consistent with traffic-flow conditions where the freeway breakdown process begins. In addition, it was found that the critical occupancy point itself and the speed at which it occurs are distributed normally.