QUEUE SPILLOVERS IN TRANSPORTATION
NETWORKS WITH A ROUTE CHOICE
Carlos F. Daganzo
Department of Civil and Environmental Engineering
and Institute of Transportation Studies
University of California, Berkeley CA 94720
(January 18, 1996)
ABSTRACT
This note uses a simple network to highlight some important
properties of the traffic assignment problem with physical
queues. In particular:
- that by increasing the capacity of a congested link its
queue can grow larger,
- that the network can become oversaturated as a result of
such an "improvement",
- that even under the most favorable assumptions, and in
contrast to the conventional problem with point queues, the
network can be stable both in an oversaturated and
undersaturated state.
- that temporary disturbances can permanently reverse the
saturation state of the network, and as a corollary
- that the solution of the time-dependent problem can be
so sensitive to the input data (chaotic behavior) so as
to make it impossible to obtain reliable predictions.
These findings have deep implications vis-a-vis current
efforts to "solve" the dynamic traffic assignment problem by
means of detailed network models because (as in weather
forecasting) it may be impossible to obtain input data with the
required accuracy to make even rough predictions of link flows
and times.
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Last update 6/11/96