EPDM Coatings
rvupgradestore.com Composet Products Custom Yacht Interiors

Author Topic: "percent Grade" ratings  (Read 2249 times)

JerryP

  • ---
  • Posts: 72
"percent Grade" ratings
« on: June 03, 2014, 07:26:57 AM »
I get the idea of grade ratings, such as 6%, 9%, etc. and the higher %, the steeper incline. However, how are they derived, and why aren't angles used? Does the percent grade indicate the ratio of elevation change (in feet, for example) over a horizontal distance (also in feet)? Such as 90 ft rise over 900ft is a 10% grade?
What are the steepest grades allowed on Interstate Highways, and other US Routes?
Jerry

"When you get to the fork in the road, take it.."

2014 Crossroads Elevation 3616
2013 F350 Powerstroke 4X4 SRW

Dan23

  • ---
  • Posts: 460
Re: "percent Grade" ratings
« Reply #1 on: June 03, 2014, 07:33:24 AM »
An 8% grade means the highway rises 8 feet in 100 feet or horizontal run, for example.

Interstates designs attempt to limit grades to 6%.
Slide-free 1998 Winnebago Brave 30'
2009 Kawasaki KLR toad on carrier
If needed, wife follows with 2010 Mazda 3 hatch or 1995 Miata

JerryP

  • ---
  • Posts: 72
Re: "percent Grade" ratings
« Reply #2 on: June 03, 2014, 07:41:08 AM »
Thanks. I thought 6% was attempted max, but I know of a couple Interstates in VA that are 7% ( e.g. I77 at Fancy Gap).
Jerry

"When you get to the fork in the road, take it.."

2014 Crossroads Elevation 3616
2013 F350 Powerstroke 4X4 SRW

Gary RV_Wizard

  • Forum Staff
  • ---
  • *
  • Posts: 61020
  • RVer Emeritus
Re: "percent Grade" ratings
« Reply #3 on: June 03, 2014, 08:02:29 AM »
Grade percentage is an angle - it's just expressed differently.  Civil engineers use grade percentage more often than degrees for terrain angles because inclines are often not constant angles. A roadbed may change degree of angle numerous times over the distance from bottom to top, but the grade percentage will express the total change. Thus a 6% hill climb may in fact be composed of greater and lesser angles at different points along the way.

Besides, grade percentage is easy to calculate when surveying.   If the ground "over there" is 12 feet higher than "here", and "there" is 240 feet away, then the grade is 12/240 or 5%. Calculating degrees is more arduous!  :)
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Ned

  • Former Staff
  • ---
  • Posts: 25574
  • Ned and Lorna are former full time RVers
    • Have you seen Rolling Stock?
Re: "percent Grade" ratings
« Reply #4 on: June 03, 2014, 08:28:19 AM »
Trigonometry is more difficult than arithmetic :)
-- Ned -- Fulltimer 1997-2013
1997 Holiday Rambler Endeavor LE
2007 GMC Canyon

Molaker

  • ---
  • Posts: 5766
  • We don't camp. We tour.
    • Pumpkin and Us
Re: "percent Grade" ratings
« Reply #5 on: June 03, 2014, 01:06:52 PM »
Trigonometry is more difficult than arithmetic  :)
Used to be...then they invented the modern day calculator like the HP Scientific.  With that introduction, they made arithmetic as difficult as trigonometry for me, anyway. :)
Tom & Joyce and Ditto the "don't tell her she's a dog" Westie
U.S. Navy (Ret)
2014 Winnebago ERA 70X 24' class B Sprinter chassis

gwcowgill

  • ---
  • Posts: 2268
  • Retired USAF, Retired Auto Instructor Dade Cty Sch
Re: "percent Grade" ratings
« Reply #6 on: June 03, 2014, 01:12:38 PM »
Trigonometry is more difficult than arithmetic :)

Slide rules worked well for figuring glide slope and runway slopes. Today's student doesn't even have to think with modern day calculators.
2009 Bounder 36B, 2014 Honda CR-V, various grandchildren when school is out. KG4LHS
2014 Honda CRV Toad,
2014 Jeep Grand Cherokee Toad

Ned

  • Former Staff
  • ---
  • Posts: 25574
  • Ned and Lorna are former full time RVers
    • Have you seen Rolling Stock?
Re: "percent Grade" ratings
« Reply #7 on: June 03, 2014, 01:21:48 PM »
Being able to do the calculations doesn't mean the user understands the results.  Why don't we measure grades in radians? :D
-- Ned -- Fulltimer 1997-2013
1997 Holiday Rambler Endeavor LE
2007 GMC Canyon

gwcowgill

  • ---
  • Posts: 2268
  • Retired USAF, Retired Auto Instructor Dade Cty Sch
Re: "percent Grade" ratings
« Reply #8 on: June 03, 2014, 05:03:02 PM »
Being able to do the calculations doesn't mean the user understands the results.  Why don't we measure grades in radians? :D
Wow, I thought we only needed the correct answer :) :) :) :) :) :) :) :)
2009 Bounder 36B, 2014 Honda CR-V, various grandchildren when school is out. KG4LHS
2014 Honda CRV Toad,
2014 Jeep Grand Cherokee Toad

Frizlefrak

  • ---
  • Posts: 3575
  • El Paso, Texas
Re: "percent Grade" ratings
« Reply #9 on: June 03, 2014, 08:33:35 PM »
I had an algebra teacher in high school that for the test would give you the question and the answer.  You had to show the work, and then explain what it meant.  It's a wonder I graduated.

I always wondered how grades were figured too.  Always just had a feel for how steep the climb was based on the number, but not the science behind it.....or the math behind it rather.
2014 Ram 2500 Cummins
2012 Palomino 30' TT

gwcowgill

  • ---
  • Posts: 2268
  • Retired USAF, Retired Auto Instructor Dade Cty Sch
Re: "percent Grade" ratings
« Reply #10 on: June 03, 2014, 09:05:11 PM »
If it hadn't been for my oldest daughter, I would never had made it through college algebra.... >:(
2009 Bounder 36B, 2014 Honda CR-V, various grandchildren when school is out. KG4LHS
2014 Honda CRV Toad,
2014 Jeep Grand Cherokee Toad

Jeff

  • Forum Staff
  • ---
  • *
  • Posts: 8989
Re: "percent Grade" ratings
« Reply #11 on: June 03, 2014, 10:18:10 PM »
If it hadn't been for my oldest daughter, I would never had made it through college algebra


I made it through a few semesters of college algebra and advanced math but when my oldest daughter hit  high school advanced math the result of me trying to help her understand the solution always ended up "We don't do it that way Dad." After taking my solution to school she admitted the teacher said it was "An alternative way to find the answer."

jubileee

  • ---
  • Posts: 314
Re: "percent Grade" ratings
« Reply #12 on: June 03, 2014, 11:09:28 PM »
A 45 degree angle is a 100 percent grade

Ned

  • Former Staff
  • ---
  • Posts: 25574
  • Ned and Lorna are former full time RVers
    • Have you seen Rolling Stock?
Re: "percent Grade" ratings
« Reply #13 on: June 04, 2014, 07:37:08 AM »
A 45 degree angle is a 100 percent grade

Or 0.785398163 radians :)
-- Ned -- Fulltimer 1997-2013
1997 Holiday Rambler Endeavor LE
2007 GMC Canyon

Gary RV_Wizard

  • Forum Staff
  • ---
  • *
  • Posts: 61020
  • RVer Emeritus
Re: "percent Grade" ratings
« Reply #14 on: June 04, 2014, 07:55:12 AM »
For you geometry and trigonometry fans, the % grade expresses the tangent of the angle of climb. It uses percentage rather than a decimal, but it's the same number.

A grade of 6% (tangent .06) is 3.43363036 degrees. See why highway engineers like to use percent rather than degrees?
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Ned

  • Former Staff
  • ---
  • Posts: 25574
  • Ned and Lorna are former full time RVers
    • Have you seen Rolling Stock?
Re: "percent Grade" ratings
« Reply #15 on: June 04, 2014, 08:12:56 AM »
A grade of 6% (tangent .06) is 3.43363036 degrees. See why highway engineers like to use percent rather than degrees?

It doesn't sound so steep when you put it in degrees.
-- Ned -- Fulltimer 1997-2013
1997 Holiday Rambler Endeavor LE
2007 GMC Canyon

anniemae

  • ---
  • Posts: 131
Re: "percent Grade" ratings
« Reply #16 on: June 04, 2014, 08:43:08 AM »
That's why the signs read;  ie.  6% OVER three miles.  Good explanation Gary, as always.

 

Hosted by Over The Network