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Sub-problem 3a - Page 3 of 9

ID# C103A03

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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