max roadway grade 1

[martin888888]

I have a 7000' private access road to a energy facility. It will be used by tractor trailers hauling fairly heavy loads. 25-50 trucks per day. Would a 12% grade for a 1000' stretch of this road be good design? The rest of the road will be at about 8% and less.

 

[Ron]

That's pretty steep for a tractor trailer. Is there a potential of ice? Is it rainy? 1000 feet makes it more tolerable, but still a strain going up and a potential safety hazard going down.

 

[civilman72]

on such a steep road, I would be concerned with getting the surface water off of the pavement, so drainage would need to be considered, especially over a long distance (like 1000').

 

[francesca]

Are they going to be loaded going uphill or downhill?

 

[Hoagie]

12-percent max is fine to use...it's the same as the fire code's max grade for access.

 

[MiketheEngineer]

With that steep of grade and loaded trucks - you might consider adding a "run away" stop where a driver could dump his truck and get stopped. Simply a pull off at a slight angle to roadway that has an upgrade to gradually slow the truck. Some people put "stopping material" in the bed to really slow the truck and basically bury the tires - like a foot of sand or some other engineered material.

 

[oldestguy]

Any curves? If so, I'd do no super elevation, due to likely slow speeds.

 

[Ron]

Hoagie...the fire access thing is a unique situation that might or might not occur...the considerations of the OP occur daily...so his design must accommodate that.

I agree with MikeTheEngineer...provide a "safety valve"...use gravel as a shoulder material to allow stopping in the event of an issue.

In my opinion, 12 percent is too much for a typical condition. I make that statement as an engineer and a former tractor-trailer driver!

 

[Hoagie]

To the original poster: The AASHTO green book will is a recognized standard for horizontal and vertical geometrics. I would suggest you take a look at it before putting in any unneccessary safety measures. Any professional truck driver worth his salt will should have no problem coping with such a moderate grade.

 

[martin888888]

Thanks for the information. I am able to get our maximum grades down to 9.8% over that 1000' stretch with the rest of the site at maximum 6%. Very usable for loaded tractor trailers.

 

[TGLG]

Watch your grade breaks.
When dealing with steep grades, it's easy to inadvertently create a situation where the breakover is sufficient to cause the landing gear on a trailer to catch on the pavement as the tractor crests the rise.
If the landing gear hits the pavement hard enough it can stop the trailer dead in its tracks and pop the trailer's kingpin up and out of the tractor's fifth wheel.

 

[martin888888]

Using vertical curves with K values per AASHTO.

 

[dik]

TGLG: You can build a 'transition' slope of 30' or 40' at the base and crest of the grade. This will prevent interference with any parts of the trailer unit.

Dik