Engineers and planners involved in design need to establish performance reliability in the case of transportation networks. I am examining a paper by Professor Michael Bell of the University of Newcastle in the Transport Operations Group. Bell splits the idea of network reliability into two dimensions; the connectivity of the network, and performance reliability.

Reliability is a measurement of the infrastructure of the roads, bridges, tunnels, etc., as well as the behavioral responses of the user. Bell provides an example of network reliability as should a piece of the infrastructure fail, the impact of the user will be dependent on how well the network can adapt. Bell defines a network as reliable “if the expected trip costs are acceptable even when users are extremely pessimistic about the state of the network.”

To examine network reliability Bell sets up a game between a user who wants a path to minimize the expected trip cost and another player who is imposing link costs on the user. As in class, this is a two-player, non cooperative, zero-sum game. The main theory that Bell proposes in playing this game is that the Nash Equilibrium for this game will give a measure of network reliability since it will give the expected trip cost is the user is extremely pessimistic about the state of the network. Here the other imposing player represents that pessimism by adding costs to links. This game is essentially trying to see how a user will react if he/she knows that there is something in the network that could increase the expected cost such as traffic.

Professor Bell finds that at the Nash Equilibrium the user is unable to decrease the expected trip cost by changing the path and the other player cannot increase the expected trip cost by changing the link cost. This means that the network reliability is not so much a function of the reaction of the user to network pessimism but more a function of the initial setup of the network itself. This important information for a designer because it allows them to better design their networks knowing the importance of the initial setup to the expected cost of the user.

Bell, Michael G. “A Game Theory Approach to Measuring the Performance Reliability of Transport Networks.” Transportation Year Part B 34 (2000): 533-545.

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