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JNMeister

PPI Exam Cafe: Transportation AM

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I'm taking the Civil: Transportation Depth Exam in less than two weeks and I'm stumped on one of the PPI: Exam Cafe AM Transpo questions. The solution said it was found in the Green Book but, I was only able to find the cross slope recommendation (1.5%-2%). I realize I can eliminate two using the cross slope and logically eliminate the gravel shoulders. But, is that what I'm suppose to do or is the ANSWER actually in the Green Book? Here is the question:

Problem 1: Transportation

A rural divided highway has an average daily traffic of 40,000 veh, with a design hour volume of 4,000 vehicles and a peak directional volume of 2500 vehicles. The commercial traffic is 5%. For a design speed of 70 mph, which of the following designs would be most appropriate?

a. four 12ft wide, paved lanes, with 8ft gravel shoulders and a cross slope of 1.5%

b. four 12ft wide, paved lanes, with 8ft paved shoulders and a cross slope of 4%

c. six 12ft wide, paved lanes, with 10ft paved shoulders and a cross slope of 2%

d. six 12ft wide, paved lanes, with 10ft gravel shoulders and a cross slope of 1%

SOLUTION: Using the AASHTO Green Book, for high traffic volumes, six lanes, and 10ft shoulders are desirable. The median should be at least 40 feet wide, and the cross slope of the pavement should be at least 1.5%. The answer is C.

Thank you!

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the key word is "Rural hwy" . Look up in the Green Book in the list of contect for the chapter Rural Hwy and find your data. I don't have book with me at work, if I find it, I'll send the page (but it there).

You just need scroll this book very carefull. There are usulay enough questions from this book on the exam. You shoud be able to find your info quick.

Good luck

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Meister - I just posted a question specifically about the PPI exams, that is, can you print out the questions for study purposes, or do you need to be at your computer?

And I agree w/the above poster -the answer is in the Green Book, typical cross sections.

Good luck with your studies!

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i cant't find this on green book. anyone found it yet?

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Well it takes a little detective work. On page 314, it states that high speed highways carrying large number of trucks should have usable shoulders of 10 feet minimum.

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ok, Green Book p. 455. It said that Lane width should be 12', normal cross slope is 1.5-2%. on page 311 is dicussed lane width of roadway for high speed. It took me a while to find all this info, and my boook is tabed! That is a key to pass it, know your references as good as possible. Easy to say, hard to do. I am trying.

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Thank you all for your replies. I'm sort of glad to hear that it was hard to find for you as well, the solution made it sound like it was in one place or chart.

As for the PPI problems, they are on the computer and NOT easy to print. Honestly, I'm not sure how much I'm going to use them besides emergency examples on the exam. They are pretty difficult, in my opinion, more difficult than the 6-minute solutions.

Starting to stress... so much left to practice, read, and tab! Good luck to all.

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This type of question requires only a little bit to look up and the rest is by deduction.

The lookup part is the number of lanes. HCM shows that for 70 mph with LOS = A (Assuming this is the design LOS. If provided, this would affect the number of lanes.), the flow rate is about 900 pc/h/ln. Using peak dir. volum of 2500, this mean you need 3 lanes to accommodate the peak flow in one direction. This narrows your answers to c and d.

The deduction part is about cross-slope, not the shoulder, because shoulder design for rural or urban environments isn't as crucial as cross-slope. The minimum cross-slope is mostly always 1.5%, thus eliminating answer "c", leaving us with "d".

This is a typical lookup/deduction question on the exam which tests a person's critical analysis skills rather than the rote manner of just looking up a table/graph or plugging and chugging an equation.

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guys, Can't find the flow rate in the HCM, where is it?

HCM (2000)Exhibit 21-2 "LOS Criteria for multilane highways" has max flow rates up to 60mi/h.

Edited by miloc

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don't remember exactly in what chapter (I don't have it with me at work; probably somewhere in ch. 20-23 or check out ch.9). Make your self a note:

Free Flow Speed for rural area -70mph, for urban -75mph

good luck tomorrow

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