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One of the major issues in the analysis of any traffic system is the analysis
of delay.
Delay is a more subtle concept.
It may be defined as the difference between the actual travel time on a given
segment and some ideal travel time of that segment.
This raises the question as to what is the ideal travel time.
In practice, the ideal travel time chosen will depend on the situation; in
general, however, there are two particular travel times that seem best suited
as benchmarks for comparison with the actual performance of the system.
These are the travel time under free flow conditions and travel time at
capacity.
Most recent research has found that for highway systems, there is comparatively
little difference between these two speeds.
That being the case, the analysis of delay normally focuses on delay that
results when demand exceeds its capacity; such delay is known as queuing delay,
and may be studied by means of queuing theory.
This theory involves the analysis of what is known as a queuing system, which
is composed of a server; a stream of customers, who demand service; and a
queue, or line of customers waiting to be served.
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