NCESS Practice Exam Problem 501

[nightwing]

Does anyone know how to solve the NCESS Problem Exam Transportation Depth Problem 501?

The problem is a HCM LOS Freeway problem. The uses a different equation and not the FFS equation. They use BFFS as the Design Speed (60 mph).

 

[JGipe1]

I did the problem, but don't have the book on me. Did they use HCM 2000 or HCM 2010?

 

[John QPE]

Can you post the problem, I don't feel like looking for my book.

 

[jose_maria]

Does anyone know how to solve the NCESS Problem Exam Transportation Depth Problem 501?

The problem is a HCM LOS Freeway problem. The uses a different equation and not the FFS equation. They use BFFS as the Design Speed (60 mph).

They have an errata out for this problem because it was based on HCM 2000 instead of HCM 2010. 

Check out the revised solution: http://ncees.org/wp-content/uploads/2012/11/2015-Civil-TRN-errata.4-10-15.pdf

In this revised case they tell you the "measured" FFS so you can just take that value and run. However, if "measured' FFS is not provided, make sure to use the FFS equation from HCM 2010 for interstates.

 

[cogborn84]

When I did the problem I just treated the BFFS much like I would a multilane highway and used 60 mph in the problem as opposed to the usual (75.5, or whatever it is, don't have my book on me). I thought it was a little weird, but ended up with the right answer once I was done so I figured it must be an exception or something. Glad to know there is an errata. Thanks for sharing @jose_maria. I will have to check out the other question in that errata too. 

 

[JGipe1]

Hopefully when we get the real exam, the first problem will have an error too and we can all freak out.

 

[ngmakhlo_PE]

Hopefully when we get the real exam, the first problem will have an error too and we can all freak out.

Freak out even more...

 

[nightwing]

They have an errata out for this problem because it was based on HCM 2000 instead of HCM 2010. 

Check out the revised solution: http://ncees.org/wp-content/uploads/2012/11/2015-Civil-TRN-errata.4-10-15.pdf

In this revised case they tell you the "measured" FFS so you can just take that value and run. However, if "measured' FFS is not provided, make sure to use the FFS equation from HCM 2010 for interstates.

Thank you.

So if the question has measured FFS we can use that as the FFS? Also, if we had to calculate the FFS what would you use as TRD? Does Commuter traffic familiar with facility mean fp = 1?  What would you as TLC? Thank you again.

 

[cogborn84]

If the question gives you a measured FFS then you do not need to calculate another FFS. So you will not use TRD, or Tlc in this problem. You just jump right to the 55 mph FFS curve. Refer to Exhibit 11-7 in the HCM, pg 11-10. You go straight to step 3 in this case.

So the steps for this are:

Select 55 mph as FFS curve, note the breakpoint and the total capacity (ie 1800 breakpoint, 2250 capacity) for use later.

Calculate Vp (fHV is the toughest part, but just consists of a formula and a lookup)

Check Vp against the breakpoint and capacity that you took note of earlier (or go look at those now)

If Vp > Capacity, LOS F

If Vp < Capacity, proceed with Density equation, but check Vp < 1800 to see if you need to adjust the speed in the density equation.

Calc Density

Then look up the density and correlate the LOS using Exhibit 11-5, p. 11-7 HCM

 

[ngmakhlo_PE]

If the question gives you a measured FFS then you do not need to calculate another FFS. So you will not use TRD, or Tlc in this problem. You just jump right to the 55 mph FFS curve. Refer to Exhibit 11-7 in the HCM, pg 11-10. You go straight to step 3 in this case.

So the steps for this are:

Select 55 mph as FFS curve, note the breakpoint and the total capacity (ie 1800 breakpoint, 2250 capacity) for use later.

Calculate Vp (fHV is the toughest part, but just consists of a formula and a lookup)

Check Vp against the breakpoint and capacity that you took note of earlier (or go look at those now)

If Vp > Capacity, LOS F

If Vp < Capacity, proceed with Density equation, but check Vp < 1800 to see if you need to adjust the speed in the density equation.

Calc Density

Then look up the density and correlate the LOS using Exhibit 11-5, p. 11-7 HCM

To save some time you don't NEED to adjust the speed if the Vp is greater than the breakpoint and solve for density, you can calculate Vp, refer to table 11-17, see where your Vp falls in relation to the FFS and the target LOS and determine your LOS from there. Any time saved is crucial. Good luck everyone!

 

[jose_maria]

Goodluck to everyone. Thanks for all of the help. 

 

[wannacape]

I assumed N (Number of lanes) will be 4 when I solved this problem since it says four lane freeway. So a freeway is always called by adding number of lanes in both direction? I thought they were giving the number of lanes in analysis direction, afterall the freeway directions operate independently I assume??

 

[jose_maria]

I assumed N (Number of lanes) will be 4 when I solved this problem since it says four lane freeway. So a freeway is always called by adding number of lanes in both direction? I thought they were giving the number of lanes in analysis direction, afterall the freeway directions operate independently I assume??

Generally when a question says something like "4 lane freeway" it means 4 lanes total in both directions. So you would use N = 2 (Number of lanes in the analysis direction). 

 

[ngmakhlo_PE]

I assumed N (Number of lanes) will be 4 when I solved this problem since it says four lane freeway. So a freeway is always called by adding number of lanes in both direction? I thought they were giving the number of lanes in analysis direction, afterall the freeway directions operate independently I assume??

N always equals the number of lanes in ONE direction of the freeway, highway, or whatever roadway given. So unless the question says, 2-lanes in one direction then know that when they say 4 lane freeway, take half of that as the number of lanes in one direction.

 

[wannacape]

N always equals the number of lanes in ONE direction of the freeway, highway, or whatever roadway given. So unless the question says, 2-lanes in one direction then know that when they say 4 lane freeway, take half of that as the number of lanes in one direction.

Thank you ngmakhlo