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Climbing Lane Average Travel Speed

Christopher Holzer
NDDOT
Climbing Lane Average Travel Speed was posted on July 6th, 2017 at 12:23 PM EDT
regarding Chapter 15: Two-Lane Highways

Hello, I am attempting to perform a climbing lane analysis. I am using HCS7 and the results show a significantly slower Average Travel Speed (ATS) WITH a climbing lane than without a climbing lane. This does not make sense to me. Has anyone else experienced this? If yes, how did you correct it?

Inputs were: shoulder width = 8ft, lane width = 12ft, segment length = 3mi, class 1 highway, analysis direction volume = 112vph, opposing direction volume = 75vph, uphill grade = 3.9% for 1.2mi, PHF = 0.88, Trucks = 45%, Recreation Vehicles = 4%, NPZ = 50%, 5 accesses per mile, estimated FFS = 65mph.

Vishal Khanapure
University of Florida
RE: Climbing Lane Average Travel Speed was posted on July 6th, 2017 at 3:52 PM EDT

This is an anomaly where the Lde value was not always set to zero for some data sets with climbing lanes – as was the case with yours. We have tracked down these conditions to generate an updated version that will properly set this value to zero – we have sent you the download link. The updated results will show ATS as 53.6 mi/h without the climbing and 61.1 mi/h with the climbing lane – increasing as expected with the LOS improving from B to A.

Scott Washburn
University of Florida
RE: Climbing Lane Average Travel Speed was posted on July 9th, 2017 at 3:03 PM EDT

Christopher:

I get different results from those given by Vishal. Can you clarify the following with regard to your listed input values:

  • You give values for lane width, shoulder width, and access point density, along with an "estimated FFS = 65 mph". However the FFS estimation equation also requires an input for Base FFS. Are you actually using a "measured" FFS of 65 mi/h (in which case the lane/shoulder widths and access point density values are not used), or did you also use a BFFS value that you did not list?

  • A climbing lane analysis uses some different calculation parameter values relative to a passing lane on level/rolling terrain, and can be quite sensitive to the segment/passing lane length inputs. You mention that the segment length is 3 mi and that the length of the grade is 1.2 mi. What exactly is the distance configuration of the segment outside of the 1.2 mi upgrade--e.g., the other 1.8 mi is before the passing lane, after the passing lane, or split before and after the passing lane?

If you want to contact me directly with this information, please feel free. My contact info is at http://swash.essie.ufl.edu/.

Christopher Holzer
NDDOT
RE: Climbing Lane Average Travel Speed was posted on July 11th, 2017 at 2:26 PM EDT

Vishal, Thank you for your help. Yes, the results seem reasonable now.

Scott, The "Estimated Base Free Flow Speed" is 65mph.

Sincerely, Christopher

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