Some observations on speed-flow and flow-occupancy relationships under congested conditions

There is a need for a better understanding of freeway operations under congested conditions. Not only are major freeways in many cities congested several hours a day, but intelligent vehicle-highway system programs to be able to function effectively under all conditions, aggregate traffic behavior under all conditions needs to be accurately modeled. Three models for congested flow-occupancy data have been put forward in the past. Using data from the Highway 401 freeway management system in Toronto, evidence in support of any of those is sought, as it is for implied models of speed-flow relationships. The data suggest that all three models can be supported. Each may be appropriate under different conditions.