Updating Turn Probabilities at Intersections in Response to Traac Incidents

Urban road traac simulators sometimes require the turn probabilities at the intersections of the network they are simulating. This report describes a method for updating the given probabilities following the occurrence of a traac incident. Taking Dial's proportional assignment as the model of driver route choice behavior, we use a variant of Dial's algorithm to assign traac to the turns of the network. We rst estimate the origin and destination of traac prior to the incident by computing an OD matrix (approximately) consistent with the assignment and the turn probabilities in normal traac conditions. We then work backwards from the assignment in the changed conditions and the above OD matrix to determine a new set of turn probabilities appropriate in the new conditions. We validate this method on the urban networks constituting the test suite of the TRITRAM simulator. Quail from RTA Traac Technology Branch, for their assistance in reviewing the paper and suggesting some of the evaluation procedures. Thanks also to Melissa Dobbie and Jee Wood from CSIRO for their help with statistics.