Grade of this road?

[DSS5]

There's been a lot of Facebook chatter about how this access road to a new apartment complex in Boone, NC is going to be unsafe in the winter, especially because it is shaded and faces Northwest (toward the prevailing winds).

However, my question is this: in the report given to the county, the builders claimed the road would have a 15% grade. But this looks steeper than that for sure. Can anyone who is more of a road expert give an estimate on the grade of the road?

[amroad17]

First, what idiot allowed this to be built?
Second, even though this looks veeerrrryy unsafe (even when dry), the builders did a nice job.

[DSS5]

First, what idiot allowed this to be built?
Second, even though this looks veeerrrryy unsafe (even when dry), the builders did a nice job.

The entire development, including the road, is located squarely within Watauga County and not the town of Boone. The county's lax standards when compared with the municipalities (Boone and Blowing Rock) are well known. In addition to the dangerous access road, several residents are currently living in hotels because of construction delays and failed inspections.

[agentsteel53]

looks like the hill is almost exactly tall as it is long.  45 degree angle at the tree line.  100% grade.

the question is, how far of an offset towards the foreground is there for the road to take a diagonal route, as opposed to straight up and down.

my eyeballing is "approximately 3 times as long as tall", so call it a 33% grade.

I may have lost a sine/arcsine conversion in there; I haven't done this stuff in years. 

[NE2]

Easiest way to measure: take a spirit level and a protractor, and find the angle between the road and horizontal. Then convert that to a percent grade.

[Alps]

looks like the hill is almost exactly tall as it is long.  45 degree angle at the tree line.  100% grade.

the question is, how far of an offset towards the foreground is there for the road to take a diagonal route, as opposed to straight up and down.

my eyeballing is "approximately 3 times as long as tall", so call it a 33% grade.

I may have lost a sine/arcsine conversion in there; I haven't done this stuff in years. 

I eyeball it at 5 times longer than tall from treeline to treeline, around the switchback. 20%. 15% would be nearly 7 times longer than tall.

[agentsteel53]

how is "grade" generally defined?  average grade, likely, but over what length?  the entire drop?

this becomes akin to measuring the length of a coastline.  at some point, you'll run into some pretty useless numbers if you measure every pebble of road - but if a road is 3 miles of steady 5%, except with a 15% drop in the middle over 1000 feet, shouldn't that be taken into account?  500 feet?  100?

[briantroutman]

how is "grade" generally defined?  average grade, likely, but over what length?  the entire drop?

This is something I've wondered, and I'm sure there is a generally accepted practice in engineering circles. At the extreme, if you measured the grade on I-80 from New York to San Francisco, it would come to about 0%.

There's a section of PA 487 heading north from Red Rock into Rickets Glen State Park which is posted 18%, but I'm sure there are short sections that are greater than that. The actual maximum immediate angle at any given point may come into play with trucks that are loaded and can only tolerate a certain angle for cargo, etc.

..the photo brought to mind this cartoon from a Volkswagen promotional book from the '60s with a bunch of New Yorker-type cartoons. One showed a Beetle approaching a hill with a warning sign "40% Grade - Close Glove Compartment"

[Kacie Jane]

I'm no engineer, and this is just a guess being pulled out of my ass.  But my guess would be the average over the distance where the absolute grade is over some minimum threshold.

[J N Winkler]

I think 33% is a bit too high--I would put it within a few percentage points of the builders' 15% claim.  (Even that is far too high given the winter traction issues.)  There is little variation in the road width in the near and far portions of the picture, which is a sign that it has been taken with an extreme telephoto lens, which also tends to foreshorten horizontal distance and thus make grades look much steeper than they actually are.

[Avalanchez71]

I can see some kids trying to get some youtube video footage getting hurt pretty bad with that build.

[NE2]

it has been taken with an extreme telephoto lens, which also tends to foreshorten horizontal distance and thus make grades look much steeper than they actually are.

This. Go out there and measure it yourself, DSS5.

[hbelkins]

Doesn't look that unsafe to me. There are state-maintained roads in Kentucky and West Virginia that are worse than that.

[1995hoo]

I can see some kids trying to get some youtube video footage getting hurt pretty bad with that build.

[jeffandnicole]

There is little variation in the road width in the near and far portions of the picture, which is a sign that it has been taken with an extreme telephoto lens, which also tends to foreshorten horizontal distance and thus make grades look much steeper than they actually are.

Looking at the rooftops, they are slanted slightly down to the right. Tilting the screen to level them produces less of a hill as well.

[corco]

Yeah, that's no worse than the road down from my parents' house in Idaho (which is covered in snow all winter). The people who live up there will figure it out. I'd guess 20% max.

[ET21]

I love the little parking outset just before the hairpin. Must be for that emergency accident 

[DSS5]

I love the little parking outset just before the hairpin. Must be for that emergency accident 

Passing zone for large vehicles, perhaps. You can see the two pickups getting pretty close to each other

[Alps]

As for how engineers measure grade, it's simple - you draw a line down the middle of the road (or a lane line, shoulder line, gutter, etc., but let's use the middle for simplicity, since it's what's usually used for a 2-lane road like this). Your line would not follow every pebble, but at the same time, you wouldn't cut through the top of a hill. Think of it as dropping a 2-inch thick rubber hose on the ground. The shape the hose takes will be a smooth series of curves and tangents, and that's your best approximation of grade.

[agentsteel53]

I think 33% is a bit too high--I would put it within a few percentage points of the builders' 15% claim.  (Even that is far too high given the winter traction issues.)  There is little variation in the road width in the near and far portions of the picture, which is a sign that it has been taken with an extreme telephoto lens, which also tends to foreshorten horizontal distance and thus make grades look much steeper than they actually are.

I had the opposite analysis - those houses at upper left appear pretty distorted, which implies to me a wide angle held non-level to the horizontal.

[formulanone]

I love the little parking outset just before the hairpin. Must be for that emergency accident 

It's a little spectating area for watching maximum hoonage.

[Kacie Jane]

As for how engineers measure grade, it's simple - you draw a line down the middle of the road (or a lane line, shoulder line, gutter, etc., but let's use the middle for simplicity, since it's what's usually used for a 2-lane road like this). Your line would not follow every pebble, but at the same time, you wouldn't cut through the top of a hill. Think of it as dropping a 2-inch thick rubber hose on the ground. The shape the hose takes will be a smooth series of curves and tangents, and that's your best approximation of grade.

That's how you measure grade at a specific point.  But when a sign says a road has a grade of X%, is that the grade at a specific point, or is it the average grade over a section? And if the latter, how do they decide what section?

[Kniwt]

A bicyclist logged their ride up this hill (just today!) on strava.com, which recorded it as 0.4 mile at an average grade of "only" 12.1%. From the elevation chart, it appears a bit steeper near the start and a bit less steep near the top.

http://app.strava.com/segments/5191841

[Takumi]

I love the little parking outset just before the hairpin. Must be for that emergency accident 

It's a little spectating area for watching maximum hoonage.

I give this road an A-

[NE2]

Who wants to bet strava.com is using an outdated elevation model?