6% of what?

We have all traveled on mountainous roads and have seen the caution signs which read...6%,3%,etc. grade next few miles. I was wondering if anyone knows what percentage of what dimension they are referring to. I think it means a percentage of 1 mile i.e. if you travel 1 mile you will drop 6% of a mile(roughly 350 ft.). I e-mailed Caltrans once but they never returned an answer, so I am asking OOT.

[Patrick del Poker Grande]

I think that's it. If it's really keeping you up at night, I can ask my wife - she's a traffic engineer. I'm sure she'll know this crap. I do remember something being funky about some of these things, though, like if they said grade or something else, it meant two different things.

[jason_t]

That's exactly what it is: the ratio of difference in elevation to difference in distance expressed as a percentage.

[The Goober]

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That's exactly what it is: the ratio of difference in elevation to difference in distance expressed as a percentage.

[/ QUOTE ]

So a street that goes up at a 45 degree angle would be a 100% grade? Or is elevation vs. the hypotenuse, so it'd be ~70% grade?

[offTopic]

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[ QUOTE ]
That's exactly what it is: the ratio of difference in elevation to difference in distance expressed as a percentage.

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So a street that goes up at a 45 degree angle would be a 100% grade? Or is elevation vs. the hypotenuse, so it'd be ~70% grade?

[/ QUOTE ]

rise / run

45 degrees = 100% grade

[Cancuk]

well here in Canada, like the rest of the world (outside of the Us and UK), we use the much more user friendly metric system. where the percentage of grade shown is the percentage of meters that you drop in a 1000M span, which is known as a kilometer.
so, 10% grade would be 100 meters.
cheers.

[offTopic]

[ QUOTE ]
so, 10% grade would be 100 meters.
cheers.

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That's, what, 82 meters in the US?

[BadBoyBenny]

I spent a summer grading roads for a private excatavtin company in Colorado. We would measure our grades at 50 foot intervals. So every 6 inch rise or drop was 1% grade. We were not allowed to build a road with more than an 8% grade that lasted for more than half a mile if there was no alternative route for a fire truck. I don't know if that was company policy or state regulation.

Once slopes (not roads usually embankments, or the like) got over 20% we would use ratios like 2:1 grade for a 33 degree slope or 1:1 for a 45 degree.

[Brainwalter]

[ QUOTE ]
well here in Canada, like the rest of the world (outside of the Us and UK), we use the much more user friendly metric system. where the percentage of grade shown is the percentage of meters that you drop in a 1000M span, which is known as a kilometer.
so, 10% grade would be 100 meters.
cheers.

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Lol this post is so dumb.

[ QUOTE ]
I think that's it. If it's really keeping you up at night, I can ask my wife - she's a traffic engineer. I'm sure she'll know this crap. I do remember something being funky about some of these things, though, like if they said grade or something else, it meant two different things.

[/ QUOTE ]

Well it isn't exactly keeping me up at night, I just thought it was a suitable topic for OOt..cleans it up a little. But yea, ask her.