A New, Comprehensive, Congestion Measure for Freeways

This article reports on a study undertaken to develop a new, objective measure that can be used to evaluate freeway congestion. The authors maintain that traffic congestion has yet to be consistently defined because such a definition will have impacts on choices regarding infrastructure investments. The new measure, called the Critical Occupancy Point (COP), is described. The COP evaluates the change in road occupancy vs. traffic speed and defines the point where congestion begins. One of the strengths of COP is the use of freeway sensor data that is already available. The authors present a case study using data from a freeway in Israel; each highway segment provides different congestion characteristics and consequently a different COP. The COP measure identifies recurrent and non-recurrent congestion and the breakdown in traffic flow before it actually occurs. The COP and the speed at which it occurs are found to be distributed normally. The authors conclude that, although this model does not identify established, concrete points at which congestion will always occur, their method can be used to help highway planners make decisions about critical areas in which infrastructure improvements may be most useful.