Sub-problem 3a - Page 3 of 9
Sub-problem 3a: Oversaturated Intersection Analysis
What is the appropriate value of the duration of
analysis when demand exceeds capacity? The default value of the duration
of an operations analysis is 15 minutes, or 0.25 hours. This value should be
used for most analyses. However, when demand exceeds capacity for a
15-minute period, it may be necessary to expand the analysis period to
ensure that all demand can be accommodated. Another alternative to be
explored in this sub-problem is to conduct a multiple time period analysis.
When should multiple time periods be considered?
If demand exceeds capacity for a given 15-minute period, the excess
demand cannot be served during this period. In reality, this demand is
shifted to the next 15-minute period. The analyst has a choice of
considering a longer duration of analysis (see above), or conducting a
multiple time period analysis. In this latter case, we would need to shift
the excess (or unserved) demand from the first time period (when demand
exceeds capacity) to the next 15-minute period. In addition to considering
this demand shift, we must also take account of the initial queue to make
sure that our estimates of control delay are realistic.
We'll now consider how to setup this problem.
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