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Calculating Effective Green times for Prot/perm left turns

Michael Vail
Quigg Engineering INC
Calculating Effective Green times for Prot/perm left turns was posted on May 23rd, 2013 at 1:17 PM EDT
regarding Chapter 18: Signalized Intersections

I'm having a bit of trouble with determination of my g/C ratio with left turn protected and permitted phasing. I know I can just use the g/C ratio given in my HCS run for calculation of required storage lengths but I can't seem to be able to figure out exactly how to determine the variables to refer to. For instance, I have a situation with leading EB & WB protected left turns followed by the permitted left turn phase (with associated EB and WB through and right turns also with green), where the g/C ratio for EB is 0.33 and for WB is 0.32. The phase times for both EB and WB are identical so I'm not sure where the discrepancy is coming from. Hopefully this makes some sense.

Brandon Nevers
Kittelson & Associates, Inc.
RE: Calculating Effective Green times for Prot/perm left turns was posted on June 11th, 2013 at 5:45 PM EDT

It's not clear what your discrepancy is. Can you clarify and also indicate the software/output report/version you are using?

As a place to start, Exhibit 31-16 of the HCM provides information on g_u and and following that is an equation for g_p (Eq 31-91). This should explain a few of the variables you are interested in.

(Edited June 11th, 2013 at 5:47 PM EDT)

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