UC Davis Institute of Transportation Studies

There have been numerous studies of the morning commute problem in a network with a single route or parallel routes with a single bottleneck on each route. Most congested networks, however, often contain more than one congestion spot along each route. In such networks, it is usually difficult to derive analytically their system-optimal traffic patterns and the tolls that realize them. In this paper, we study the morning commute problem in such a network with certain special topological features – a freeway with multiple entry/exit ramps and a surface street grid with large capacities. For this type of networks, we investigated the basic characteristics of their optimal dynamic traffic patterns and the corresponding tolling scheme, for which a graphical solution procedure was also developed. In this network, we found that at system-optimum: (1) the aggregate traffic flow on the freeway has a staircase temporal profile, and piecewise linear dynamic tolls can be imposed on a subset of ramps to achieve it; (2) among all the off-ramps in use, the ones closer to the destination are being tolled longer with higher maximum toll charges than the ones farther away from the destination; and (3) among all the on-ramps in use, the ones with larger cumulative volume-to-capacity ratios are being tolled longer with higher maximum toll charges. Some practical implications of these findings to corridor traffic management were also discussed.