road widening with no superelevation 4

[Denob]

Due to restrictions, I am to design a road with a 500' radius curve and an 800' reverse curve. Our client does not want superelevation because of the possibility of commercial development adjacent to the road.

What is the maximum design speed that I can obtain assuming only a normal crown of 2% slope?

 

[ACtrafficengr]

It's in the Green Book.

Be advised that you can expect to have increased numbers of head-on and run-off-road crashes due to insufficent super. Can you at least talk your client into a reverse crown?

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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[Denob]

Drats...I knew I would get the "look in the Green Book" response! But thanks for the reverse crown idea.

 

[BigH]

Actually, a lot would depend, I opine, on the operating speeds. For low speeds (say 30 mph) I doubt it would make much difference - for higher speeds, of course, the lack of superelevation would. Sorry my traffic books are in mothballs.

 

[francesca]

Drats...I knew I would get the "look in the Green Book" response!

Imagine having to do the job you're being paid to do!

 

[Denob]

francesca, I get paid almost nothing compared to engineers...I'm actually just an intern! But thanks for your valuable input.

 

[oudst]

might be a silly quesiton .. but what is the green book?
i am not american, just european or dutch if you want to know

 

[henri2]

Nope...not a silly question at all. When I first read it I thought it was this

http://bnibooks.com/merchant.mvc?Screen=PROD&Store_Code=BCBS&Product_Code=1557014183

since I was familiar with it and everyone in my field referred to it as the GREEN BOOK...but then I realised this thread was about geometric design of roadway....so I figured it may be this book

http://www.fhwa.dot.gov/programadmin/y2kgb.htm

 

[cvg]

henri, you are correct and as the second link shows, the green book used to be red or blue...

"A Policy on Geometric Design of Highways and Streets" published by the FHWA.

This is the primary reference for road design in the United States.

 

[henri2]

cvg, so when it was red was it referred to as the RED BOOK?

 

[ACtrafficengr]

Once upon a time, there was a red-covered book and a blue-covered book. One was for surface streets and highways, & the other covered freeway design. I forget which was which. In 1984, I believe, they combined them into the "Green Book." Apparently at the time, people were surprised that the new book wasn't purple.

------------------------------------------
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[BigH]

In India - they have the "yellow" book - the book of specfications for bridge and highway works. But, I never saw a yellow one; always it was orange. Made me wonder if I had, over the last 50 years or so, been confusing orange and yellow! Finally found out that for the Indians, old habits (word usage) died a very slow death!

 

[oudst]

ok thanx people.
we have guidelines for every kind of roads separated.
Tons of them

 

[newjerseype]

The Green Book contains tables for minimum radius for normal crown road for various design speeds but the radiuses listed are very large since they are based on very low friction factors. An alternative I have used is to use the e + f=v^2/15R equation given in the book and plug in -2% for e (superelevation), max allowable friction factor values for the design speed for f and solve for R. NJDOT has bought this methodology every time I have used it.

 

[ACtrafficengr]

NJ PE - would you specify a high-friction aggregate?

------------------------------------------
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[zabrab]

ACtrafficengr

Yes it was 1984 when they combined the Blue (rural) and Red (urban) manuals.

I was just out of school and my first position was with a state DOT; We started getting the new books in early '85 I think.
I can't tell you how many oldtimers were really bothered that the combined manual was green instead of purple. Mostly it took the form of muttering something like "Why did AASHTO do something so illogical? You combine red and blue, you get purple, not green."

 

[ACtrafficengr]

If they had called it "A Policy on Geometric Design of Streets and Highways, it might have been known as the "POGDOSH" instead of by it's cover" ;-p

------------------------------------------
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[newjerseype]

AC, I never have specified high friction aggregate when using normal crown on a curve. To tell you the truth, I've never thought to. I don't think it's necessary but it could help depending on how close to fmax you're getting.