Freeway ramp metering strategies for responding to incidents

This paper reviews some recent work involving the formulation of freeway ramp metering strategies in situations where incidents have occured. These strategies embody a two-level control structure, the first level being aggregate in nature, with the second level providing detailed ramp metering. The work performed thus far has focused on the development of a low order macroscopic model to represent incident conditions on a freeway. This low order model results from an aggregation of conditions on the freeways and pertaining to the on and off-ramps according to their locations with respect to various freeway density zones (i.e., normal zone, congested zone, and clearing zone). Overall and individual ramp metering strategies are postulated using this model and optimal control theory.