Dynamic stability, traffic equilibrium and the law of peak-hour expressway congestion

Anthony Downs’s traffic congestion analysis is given a generalized theoretical foundation. It is demonstrated that only two equilibrium saddle points-one stable, the other unstable-can be attained. Once the stable equilibrium is reached, traffic planning and control measures such as drastically increased metering and/or a metropolitan rail transit alternative must be in place so as to maintain equilibrium. If not, the expressway system eventually reaches gridlock. It is also shown that the analyses of Thomson and Mogridge parallel Downs’s analysis and lead to the same conclusion.