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The problem of oversaturation is not just one of degree but of kind - extreme
congestion is marked by a new phenomenon: intersection blockage.
The overall approach can be stated in a logical set of steps:
- Address the root causes of congestion
- Update the signalization, for poor signalization is frequently the cause
of what looks like an incurable problem
- If the problem persists, use novel signalization to minimize the impact
and spatial extent of the extreme congestion.
- Provide more space by use of turn bays and parking congestion.
- Develop site specific evaluations where there are conflicting goals.
Signalization can be improved through measures like, reasonably short cycle
lengths, proper offsets and proper splits.
Sometimes when there is too much traffic then options such as equity offsets(to
aid cross flows) and different splits may be called upon.
A metering plan involving the three types - internal, external and release -
may be applied.
Internal metering refers to the use of control strategies within a congested
network so as to influence the distribution of vehicles arriving at or
departing from a critical location.
External metering refers to the control of the major access points to the
defined system, so that inflow rates into the system are limited if the system
if the system is already too congested.
Release metering refers to the cases in which vehicles are stored in such
locations as parking garages and lots, from which their release can be in
principle controlled.
The concept of signal coordination is presented in this chapter.
Coordination in one way is simple and effective and results in better
progression.
Two-way coordination is complex and less effective.
Bandwidth is an important parameter in evaluating the efficiency of
coordination.
Further, the concepts of forward and reverse progression are introduced.
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