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Diverge Analysis - Freeway Length

Steve Tarabokija
Provident Design Engineering
Diverge Analysis - Freeway Length was posted on August 10th, 2017 at 10:59 AM EDT
regarding Chapter 13: Freeway Merge and Diverge Segments

In the HCS7 Freeway Diverge module, there is an input parameter labeled "Freeway Length, ft" (separate from the decel lane length). What defines the freeway length? I can't seem to find documentation on this in the HCM or in the HCS help menu. Thanks!

Vishal Khanapure
University of Florida
RE: Diverge Analysis - Freeway Length was posted on August 10th, 2017 at 11:23 AM EDT

The "Freeway Length, ft" input in HCS7 Diverge Analysis corresponds to the "Segment Length, ft". If you press the F1 key in the field it should display a help topic for that input. I hope this helps. Please contact me at kvishal@ufl.edu with any further questions.

Steve Tarabokija
Provident Design Engineering
RE: Diverge Analysis - Freeway Length was posted on August 10th, 2017 at 11:36 AM EDT

Thanks for the reply Vishal. It helps a bit, but I guess what I am looking for is what actually defines the limits of the segment length. For instance, HCM shows a diagram showing how to measure a accel/decel lane length or a weaving segment length. No such diagram exists to define a freeway segment length. In my situation, I have a two lane highway in one direction. There is a signalized intersection followed downstream by a diverge, with no decel lane. Would my segment length equal the length from the signalized intersection to the diverge point?
For other scenarios not similar to mine, would the segment length equal the distance from the diverge point to the nearest upstream ramp/signal/etc.? Thanks again!

Scott Washburn
University of Florida
RE: Diverge Analysis - Freeway Length was posted on August 10th, 2017 at 12:11 PM EDT

Steve: The assumed length of a diverge segment is 1500 ft. If you have an adjacent upstream on-ramp or downstream off-ramp, then you need to enter the distance from the subject ramp to the adjacent ramp(s). I am not familiar with HCS7, but maybe the length input is related to that aspect.

That being said, it sounds like you are describing a signalized multilane highway--the freeway diverge analysis methodology is not really intended for that situation.

If you want to try out an alternative, and free, software program for HCM calculations (for both the 5th and 6th editions), see:

http://swashware.com/HCMCalc

http://swashware.com/TTR_ATDM

(Edited August 10th, 2017 at 12:12 PM EDT)

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