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Work Zone Free-Flow Speed Model

Vichika Iragavarapu
Stantec
Work Zone Free-Flow Speed Model was posted on September 21st, 2018 at 2:03 PM EDT
regarding Chapter 10: Freeway Facilities Core Methodology

Equation 10-10 utilizes fsr, which is defined as speed ratio (decimal); the ratio of non-work-zone speed to work-zone speed (pg. 10-41).

I believe this needs to be the ratio of work-zone speed to non-work-zone speed to accurately estimate FFSwz.

For example, if non-work-zone speed limit is 70 mph and work zone speed limit is 40mph for a one-lane closure, Eq. 10-10 would estimate FFSwz to be 76 mph. this doesn't seem correct. However if fsr is defined as the ratio of work-zone speed to non-work-zone speed, the estimated FFSwz will for the example site will be 36 mph, which seems more reasonable.

Thoughts?

Vichika

(Edited September 21st, 2018 at 2:04 PM EDT)
Scott Washburn
University of Florida
RE: Work Zone Free-Flow Speed Model was posted on September 30th, 2018 at 2:25 PM EDT

This issue was discussed at our mid-year meeting (Austin, June 2018). In the database used to calibrate the model, there were no instances of large differences between work zone and non-work zone speeds. The equation would have to be re-calibrated to use the inverse of the speed ratio. For now, we are going to add a disclaimer that the speed ratio only applies when it is small (less than 1.2).

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