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Subproblem 5a - Page 4 of 5

ID# C305A04

Sub-problem 5a: Two-Phase Traffic Signal Control

The application of the QEM cross product check to this sub-problem is summarized as follows:

Exhibit 3-36. QEM data summary

Left turn volume 120 vph
Opposing thru volume 2,010 vph
Cross product 241,200
QEM threshold for two lanes of opposing traffic 90,000

So, the QEM cross product check suggests the need for a protected left turn.

The second left-turn protection check in the QEM involves the determination of sneaker capacity, i.e., the number of left turns that can be accommodated assuming that two vehicles proceed at the end of each permitted phase. Sneakers are considered to create extra capacity for a left-turn movement. The HCM suggests that most of the capacity for permitted left turns will be generated by sneakers whenever the through vehicle equivalence of a left turn exceeds 3.5. HCM Exhibit C16-3 provides a table that expresses the left-turn equivatents as a function of the opposing flow and the type of left turn lane (shared or exclusive). The QEM prescribes a check for sneaker capacity when the left-turn equivatents suggest that most of the capacity will be associated with sneakers.

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