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Geometry of weaving segments

Alexandre Hering Coelho
Universidade Federal de Santa Catarina
Geometry of weaving segments was posted on May 16th, 2018 at 10:21 AM EDT
regarding Chapter 12: Freeway Weaving Segments

Good morning everyone.

What would be the correct determination of the geometric characteristics of the weaving segment illustrated in this figure, involving LCfr, LCrf and Nwl? Should the segment considered one or two-sided? Could exists weaving segments with LCfr or LCrf greater than 1? On the figure I tried to classify the lanes for the determination of Nwl, considering one-sided. The lanes 4 and 5 are merging on the segment, becoming one lane to classify for Nwl. Coming from the freeway this lane counts (0 lane changes required), but coming from the ramp it doesn't (2 lane changes required). In this situation, what prevails for the classification of this lane?

Thank you for ant comment.

Joseph Fazio
RE: Geometry of weaving segments was posted on May 16th, 2018 at 11:30 AM EDT

In my opinion, the diagram indicates a one-sided weave because on p. 13-5 6th Ed. HCM the definition of a two-sided weave is "one in which at least one weaving maneuver requires three or more lane changes to be completed successfully or in which a single-lane on-ramp is closely followed by a single-lane off-ramp on the opposite side of the freeway."

In the diagram, there are no single lane ramps, and LC_FR = 0 lc and LC_RF = 2 lc. Thus, the weave segment is not two-sided.

On p.13-7, NWL is "number of lanes from which a weaving maneuver may be completed with one lane change or no lane changes."

In the diagram, Lane 1 weavers must make 2 lc, Lane 2 weavers must make 1 lc, Lane 3 makes 0 lc, Lane 4 makes 0 lc, Lane 5 weavers makes 2 lc, and Lane 6 makes 3 lc. Thus, NWL = 3 ln.

(Edited May 16th, 2018 at 11:32 AM EDT)
Alexandre Hering Coelho
Universidade Federal de Santa Catarina
RE: Geometry of weaving segments was posted on July 16th, 2018 at 6:25 PM EDT

Dear Joseph, thank you very much for your answer. Specifically about the NWL determination, the problem with the lanes 4 and 5 is similar to the example (b) of the Exhibit 12-5, page 12-6 of HCM 2010 (sorry, I don't have the 6 Ed.). About this situation, it says on page 12-7: "Because the movements have merged into a single lane, this counts as one lane from which weaving movements can be made with one or fewer lane changes." In this example from HCM, in both cases (ramp to freeway and freeway to ramp) the lane counts for the NWL determination, so there is no doubt about taking or not the merged lane in account. But in the case of my question, the lane 4 counts for NWL, but the lane 5 does not. Since they also form merging movements, so as in the HCM example, I don't know what is the correct interpretation here. Alexandre.

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