NCEES 2014 Practice Exam Ped LOS Question?

I thought platoon adjusted PED LOS was to be found by calculating the Average Spacing and then looked up in HCM table.

This was my logic on the question:

Vp = 1200/(15*6.5) = 12.3

Assume Sp = 300 ft/min

Ap = Sp/Vp = 300/12.3 = 24.37 which would be in the LOS D range, but the solution uses the Vp to find the LOS E.

Am I supposed to use Vp or Average Spacing to find the Pedestrian LOS?

For one, you can stop after you calculate vp since Exhibit 23-2 allows you to calculate the Platoon-Adjusted LOS with Flow Rate (vp = 12.3 ped/ft/min --> LOS E  -->  Answer D)

But, if you were to calculate Ap, you wouldn't assume that Sp is 300 ft/min.  Calculate Sp using Equation 17-28 (and assuming Spf = 4.4 ft/s per chapter guidance).  If you calc Ap doing this, you should get Ap = 18.9 ft^2 / ped which, again, using Exhibit 23-2 you'll also get LOS E, Answer D.

Does that help?

yes that was helpful

Thanks

i have seen 4.0 ft/s as desirable, where did you find (Spf = 4.4 ft/s)

Thanks

Tmar1no said:

i have seen 4.0 ft/s as desirable, where did you find (Spf = 4.4 ft/s)

Thanks

Click to expand...

You're welc. 

Chapter 17, page 17-46 explains you should use 4.4 ft/s for Spf (Average free-flow pedestrian walking speed).  It then provides guidance on how to adjust it for certain situations (elderly, steep grade).  I understand this is for Urban Street Segments (Chapt 17), not Off-street Facilities (Chapt 23) but I don't see any guidance for Spf in Chapt 23, do you? 

With that said, you could essentially use an Spf as low as 2.X ft/s and as high as 5.X ft/s when you are calculating Ap and you'd still fall within the range of LOS E (11 - 23 ft^2/ped) in Exhibit 23-2 and get the same answer. 

But, really, if we stick to only Chapter 23, which maybe we should, and leave Chapter 17 out of it, we can solve this problem without needing Spf.  We need only assume Sp (pedestrian speed, ft/min) - since the problem doesn't provide Sp - to solve for Ap (pedestrian space, ft^2/ped) using Eqn 23-4.  A range of values for Sp will still yield the correct answer. 

In summary, you can solve this problem 2 ways.  Use Eqn 23-3, get vp = 12.3 ped/min/ft; use Exh 23-2 to get LOS = E.  Or, use Eqn 23-4 (and assume Sp = 4.0 ft/s as you suggest), get Ap = 19.5 ft^2/ped); use Exh 23-2 to get LOS = E.