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CH-12 Weaving - LOS=F very frequent

Tony Geara
CH-12 Weaving - LOS=F very frequent was posted on September 22nd, 2013 at 4:25 AM EDT
regarding Chapter 12: Freeway Weaving Segments

I was recently given the task of analyzing weaving segments at a series of freeway interchanges along a corridor that we are improving. 12 weaving segments were identified and projected traffic flow data for AM, MD, and PM were summarized from VISUM and made ready for HCS analysis. The client asked that we use HCM2010 and not HCM2000 (accordingly we used HCS2010 for the analysis). Once the weaving analyses were run and the LOS tabulated, it was apparent that a LOS of F was predominant.

Accordingly, I went back to the manual (HCM2010) to run the calculations manually to identify the problem (assuming it could be a software patch issue) and I also tried to run the same numbers in HCS+7 (based on HCM2000) to see if there were any discrepancies.


  • It is clear that HCM2000 would have provided acceptable or slightly better LOS for most of the weaving sections; HCM2010 does not.

  • For the HCM2010 calculations: The Capacity seems to be continuously controlled by weaving demand (for our data set) and not by density; thus limiting any possibility for mitigation strategies. Accordingly, we are left with only one option: to reduce demand somehow. In other words even if we are to increase the weaving length or increase number of lanes (if possible, in most cases we already had 5 lanes) there was little or no improvement in the LOS. Weaving length would only have helped if capacity determined by density controlled.

The client would not accept an “F” for a projected LOS.

• Does anyone have any suggestions as to what would be the best approach in this case?

• Are there any provisions to override the HCM requirements?

• Any other mitigation suggestions to improve the weaving LOW?

I have attached an example of input data used that yielded an LOS=F in HCS2010 (base don HCM2010):

One-sided Freeway

VFF = 4787 veh/hr
VRF = 839 veh/hr
VFR = 2086 veh/hr
VRR = 20 veh/hr
LS=2133 ft
FFS = 63 mi/hr
Smin = 15 mi/hr
PHF = 0.95
Trucks = 5%
RV = 0%
ET = 1.5
ER = 1.2
fHV = 0.976
fp = 1.0
N = 5
NWL = 2
LCRF = 1
LCFR = 1

(Edited September 22nd, 2013 at 4:27 AM EDT)
Joseph Fazio
RE: CH-12 Weaving - LOS=F very frequent was posted on September 23rd, 2013 at 12:05 AM EDT

I used your sample data you submitted and manually performed the calculations. Since you did not provide an interchange density, I assumed 0.8 interchanges per mile. It also resulted in LOS F because weaving demand exceeded capacity.

You varied length and N in your scenarios. However, you did not try varying the configuration of the segment. Try adding lane balance at the exit gore to reduce the total number of lane changes of the FR movement, i.e., LCFR=0 lane changes and NWL=3 lanes. I derived an LOS D using your sample data.

Hope this helps.

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