Traffic Equilibration: The Case of the Twin Cities Ramp Meter Shut Off

In Fall 2000, more than 430 ramp meters in the Twin Cities metropolitan area were shut down in order to evaluate the effectiveness of the metering system. This shutdown disturbed normal traffic patterns and thus traffic equilibrium. The purpose of our research is to examine how long it takes to establish a new equilibrium after a shock to the system, and thus establish the basis for how long these traffic studies should be carried out, as transportation analysts are generally concerned with comparing two equilibrium conditions. The initial results contradict our hypothesis that as the number of weeks since the shutdown increases, the week-to-week change in volume decreases. In fact our results show that not only are the week-to-week changes in volume is greater for shutdown case than for pre-shutdown case, those changes are rising as the experiment proceeded. More research is needed to examine the question of whether and how equilibria form, and we need to examine longer time slices for analysis to consider alternative definitions of equilibria.