Measuring capacity flexibility of a transportation system

This paper describes concepts and techniques to measure the flexibility of a transportation system to accommodate changing demands and traffic patterns. Flexibility is increasingly desired as a characteristic of transport systems, particularly in light of changes in supply chains and traffic patterns, and the concern for the vulnerability of the system to both natural disasters and terrorist actions. Two approaches are described. One is based on current methods for estimating system capacity, and the related concept of reserve capacity. This results in a conservative estimate of flexibility. The second approach permits variations in the traffic pattern, in order to more fully capture demand variations that can be accommodated. The described measures are implemented on a containerized freight rail network, as a means of testing their feasibility and potential value as descriptors of system characteristics. The uses of the measures in planning, investment, and policy-making are discussed.