road gradients

[aostling]

The New York Times business section today ran an article about a new Oshkosh truck developed under a Pentagon contract. It stated that the truck could climb a 60-degree slope. I knew that was in error, and figured that somebody had meant to say "60 percent inclines."

Indeed that is the case. I left the newspaper in the coffee shop where I read it, but I see that the online version has been corrected, as you can see here: http://www.nytimes.com/2009/11/04/bu...20truck&st=cse.

What is percent slope? I've long held the belief that it is the ratio of vertical rise to distance traveled, which would be the sine of the angle (multiplied by 100 of course). But Wikipedia and my dictionaries define percent slope as the ratio of vertical rise to horizontal distance, which is the tangent of the angle. Anybody have a civil engineering textbook? I'll believe whatever that has to say on the subject.

This brings up a question as to what is the steepest slope a vehicle can manage. I've seen bulldozed firebreaks which almost defy credibility. How steep a slope can a bulldozer climb?

[edit] changed "slope" to "inclines," the word used in the NYT online article

[Lew Hartswick]

Just looked in the college Surveying book and they don't use
"Slope" as any measurement. The term is used as a description
in talking about railroads as to the "slope" of the fill to the bed from
surounding terain. Again in how to "tape" horizontal distances when
the terain slopes. ( cutting tape ) etc.
But no mention of how angles from horizontal would use it.
...lew...

[AD5MB]

grade. 6% grade, et cetera

[andy_b]

a HUMVEE is rated to climb 60% slopes, so some vehicles can certainly do it. a 60% slope looks to work out to about 30 degrees. i have a small crawler (Oliver OC-46) that can easily climb a 60% slope. the problem is i feel like i am going to flip over backwards doing it. i wouldn't doubt it could climb a 100% slope (45 degrees) but you would need balls of steel to be driving it.

andy b.

[SDL]

We used to use the ratio on road signs ie 1 in 10 as 1:10, or 1:4 etc, for a percentage its the fraction as a petcentage, so 1:10 is 10% 1:4 is 25%etc.

Steve Larner

[brian Rupnow]

I've always wondered about that myself. Wouldn't 100% slope be straight up, as in 90 degrees to horizontal?

[kendall]

Would think a 100% grade would be 45 degrees. (12:12) 50% would be 6:12 etc.

Ken.

edit: meant to say 50% would be 22.5 which equals 6:12
Being a carpenter, I find it much easier to determine the angle if I translate it into pitch

[camdigger]

IIRC, grades are measured in percentages while slopes are measured in ratios, especially when specifying "backslopes" as in the inclination of the ditch on the side of the highway is specified as backsloped 2:1 or a borrow pit is specified as backsloped 2:1 on the sides and 3 or 4:1 on the ends.

Motor scrapers should be able to negotiate at least 2:1 slopes... crawlers 1:1 watched them do it lots on assorted sites over the years. It is a bit disconcerting to watch #125,000 of D8H, K, N, or T back out of a pit dug 1:1 and come over balance on the edge Crawlers are often asked to negotiate slopes deeper than they can dig. Sometimes the operators will push up a small tapered pad at the end so the dozer will dig steeper.

FWIW, it is safer to go straight up or down a slope on a dozer. A dozer on a side slope may slide sideways down hill! Ask any operator who's done it, especially hair raising in bush country...

[The Artful Bodger]

Baldwin Street in Dunedin is reputed to be the steepest street in the world:-


35% gradient = 1:2.86

[aostling]

Baldwin Street in Dunedin is reputed to be the steepest street in the world:-

I drove up Baldwin Street when I was in Dunedin in 1995. My car, an old Datsun, strained at the grade. "I'm sure glad I don't have to drive back down this street," I thought to myself (wondering about the brakes). Only when I got to the top did I discover that it is a dead-end street!