Free Flow Speed

Hi All,

I have a question in regards to the free flow speed in the HCM. Two of the equations for FFS are

FFS = 75.4 - fLW - fLC - 3.22TRD^0.84 (Page 11-11, Equation 11-1)

AND

FFS= BFFS - fLW - fLC - fM - fA (Page 14-10, Equation 14-1)

I understand that the top one is for freeways and the bottom one is for multilane highways, but what if the problems gives the Base Free Flow Speed (BFFS) and it is a freeway (NOT a multilane highway). Can I still use the bottom equation? Thanks!

You would have to be given median and access point information. But if the problem statement directly calls out for a freeway I believe you need to use that equation. If you read the paragraph under the equation "Base FFS" it explains pretty well why you use 75.4. That value covers all speeds from 55-75 mi/hr. I'm sure someone will chime in if I am wrong on that. Good luck, I'll be taking the test next Friday as well.

Thanks...That's what I figured too. I have the Lindeburg Practice Exam (where I ran into this problem) and six minute solutions but a lot of the equations are from old references . Guess I should just stick to the NCEES Practice Exam (Most recent) and School of PE notes for the depth. Good luck to you too!

P.S There's not a lot of practice exams out there for the transportation afternoon section am I right?

Chris C said:

Thanks...That's what I figured too. I have the Lindeburg Practice Exam (where I ran into this problem) and six minute solutions but a lot of the equations are from old references . Guess I should just stick to the NCEES Practice Exam (Most recent) and School of PE notes for the depth. Good luck to you too!

Click to expand...

I ran into this problem a lot trying to study for the afternoon portion of the PE exam. The old FFS equation used BFFS instead of that new 75.4 and that isn't really reflected in any practice exams I've seen.

And no, you're right, there's definitely a lack of practice exams out there for the afternoon transportation section. I've just been using old 6-minute solutions and a few I stumbled across on Amazon (which are just ok, a lot of errors). Just making sure I know where to find the answers in the updated references, even if the solutions are outdated. Let me know if you find any good ones that reflect the new 2015 exam rubric. The one I bought was by Dr. Indranil Goswami, and while the topics were relevant, there were a lot of errors.

Yea I have mostly old ones and the most recent one from ncees. I'll be taking that one this weekend to figure out where I need to fine tune my last bit of studying.

I bought Goswami also, and have been looking at Lindeburg and Six Minute Solution as well (Have only completely went through Goswami's though). I read somewhere on here that the School of PE notes were not helpful for the Transportation Afternoon but I'm going to pretend that I didn't read that. The class seems very helpful and I'd be shocked if it didn't prepare me for the afternoon. Of course, I still need to spend time on my own tabbing and getting ever more familiar with the references, but I think I should be okay well see. Good luck to all...

Yea I heard that about School of PE as well. I actually saw their depth notes from previous classes, and the version we got for this test is much more thorough. I have a friend that took and passed with TestMasters last fall, and his notes are very similar. His biggest advice was to tab like hell. The MUTCD questions seem to be the most random and harder to prepare for. I have been trying to get real familiar with that and the Green Book over the last couple months.

Well that's a sigh of relief! Was really worried that 150+ pages worth of notes weren't going to be that useful. I think the key to the afternoon is being very familiar where all the sections are in each reference. Given the amount of pages in each reference it's virtually impossible to go through everything, just be familiar with the layout and how to use the most common tables/formulas.

FYI:

Question 501 on the latest NCEES Practice exam has an error apparently. A guy from reddit contacted NCEES and they have an errata out for this.

reddit forum: https://www.reddit.com/r/civilengineering/comments/4bs0uf/transportation_pe_exam_question_on_hcm_2010_basic/

The errata can be found here: https://cdn.ncees.org/wp-content/uploads/2012/11/2015-Civil-TRN-errata.4-10-15.pdf

That makes sense. If they give you FFS then you don't need the equation at all. You just go straight into finding flow rate and then density.