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Weaving Section Capacity

Weaving Section Capacity was posted on September 29th, 2015 at 9:43 AM EDT
regarding Chapter 12: Freeway Weaving Segments

Dear All, I have been a new user of HCM 2010 and always have this doubt about interpretation of high v/c of the weaving segment while the section LOS is at B or C. This happens especially with Nwl= 2 and when the segment capacity is 2400. As an example I have a section at LOS C while v/c = 0.95. I am struggling to find an interpretation of the same. Has anyone come across a similar situation and explained this reasonably Kind Regards

Joseph Fazio
RE: Weaving Section Capacity was posted on September 29th, 2015 at 3:54 PM EDT

I have not come across the situation of high v/c with good LOS. Is there a large difference between Sw and Snw? If you can provide the v, vnw, N, and L, I will check if this situation can be re-created.

RE: Weaving Section Capacity was posted on September 30th, 2015 at 8:42 AM EDT

The Vff = 119 Vrf = 2003 Vfr 2 Vrr - 10 Ls = 1000ft N = 4 Nwl = 2 Lcrf =1 LCfr = 1 This gives me an LOS B but v/c 0.93. The avearge weaving speed = 40.3 and non-weaving speed = 31 mph Please let me know. Kind Regards

Kevin Mascarina
RE: Weaving Section Capacity was posted on January 25th, 2017 at 6:47 AM EST

It is indeed possible to get a high v/c and a good LOS for weaving segments due to the methodology for calculating capacities and densities in the HCM2010.

Weaving capacity is calculated based on (1) segment capacity by density and (2) segment capacity based on weaving demand flows. The smaller of the two is taken as the final capacity. In your case, the weaving flows total 2,005 veh/h. For Nwl = 2, 2,400 pc/h is the limit. Hence, you get a high v/c ratio.

Density, on the other hand, is calculated from the average speed of ALL vehicles. This means the space mean speed of both the non-weaving and weaving vehicles. Almost 100% of weaving vehicles (i.e. 2,003 of 2,005) go in one direction, from ramp to freeway, plus your non-weaving vehicles only amount to 129 veh/h. A decent speed (subsequently density) is then expected and therefore a good LOS.

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