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PHF Use

Amy Diaz
Cobb County DOT
PHF Use was posted on June 12th, 2017 at 12:16 PM EDT
regarding Chapter 19: Signalized Intersections

In chapter 19 of HCM 6, the guide continued recommendation from the last edition of the HCM that approach PHF could over-represent so overall intersection PHF was recommended if PHF was used.

I have been following this but I am getting argument that this is only for planning and that operations should still use approach/movement specific PHF.

All the official examples I have skimmed for operations use the straight 15-minute flows and don't use PHF at all, so I'm looking to see how others are implementing PHF in operations analysis.

Tyrone Scorsone
Kittelson & Associates
RE: PHF Use was posted on June 27th, 2017 at 2:07 PM EDT

The guidance in the 6th Ed. HCM is, "If peak hour factors for each individual approach or movement are used, they are likely to generate demand volumes from one 15-min period that are in apparent conflict with demand volumes from another 15-min period, but in reality these peak volumes do not occur at the same time. Furthermore, to determine individual approach or movement peak hour factors, actual 15-min count data are likely available, permitting the determination of actual 15-min demand and avoiding the need to use a peak hour factor. In the event individual approaches or movements are known to have substantially different peaking characteristics or peak during different 15-min periods within the hour, a series of 15-min analysis periods that encompass the peaking should be considered instead of a single analysis period using a single peak hour factor for the intersection." My interpretation, of the Manual, is to use the actual 15 minute volumes when available. My experience with the PHF relates to project traffic analysis for FDOT where a PHF of 1.0 is used for future year analyses.

(Edited June 27th, 2017 at 2:08 PM EDT)

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