SO-DTA Graphical Solution Method for a Congested Freeway and One Destination

This paper studies the system optimum dynamic traffic assignment in a network consisting of a surface street grid and a congested freeway section. Vehicles can be diverted through off-ramps and on-ramps can be metered. The family of solutions are identified graphically using Newell’s queueing diagrams. Because enforcing diversion is still a technological puzzle, these results provide a benchmark for future ITS applications, and a building-block for including both, several destinations and departure time choice. This paper also shows why pricing according to marginal cost cannot work; that eliminating all queues from the freeway is always suboptimal; and that ramps near the bottleneck should be metered more severely.