Figuring grade % for bridges

[inkyatari]

OK, I'm trying to figure out a grade percentage, and I vaguely recall the formula, and I have several bicycle routing apps / websites that automatically calculate that, but here's the caveat; while these things work well for hills, valleys and the like, bridges are another story, as they don't seem to have elevation data for most of these.  Specifically, the Illinois Rt. 47 bridge over the Illinois river in Morris, IL. How would I get the  data as for the bridge's top-side-of-the-deck height?

[Rick Powell]

OK, I'm trying to figure out a grade percentage, and I vaguely recall the formula, and I have several bicycle routing apps / websites that automatically calculate that, but here's the caveat; while these things work well for hills, valleys and the like, bridges are another story, as they don't seem to have elevation data for most of these.  Specifically, the Illinois Rt. 47 bridge over the Illinois river in Morris, IL. How would I get the  data as for the bridge's top-side-of-the-deck height?

Grade is rise divided by run, and percentage grade is rise divided by run, times 100. For example, a 2% grade rises 2 feet in 100 feet of travel...2 divided by 100 = 0.02, then 0.02 x 100 = 2%. There are several apps that will get elevation over your smart phone within an inch or so accuracy via GPS triangulation. So you'd have to measure the elevation at one end, measure the length between ends, and then measure the elevation at the other end, and then perform the calculation. This would only give you the average % grade of the bridge end to end. In actuality, many river bridges are built with a hump in the middle, and the steepest grades are in the approach and not on the bridge itself, which might have a crest in the middle somewhere (a 0% grade at that point). Vertical curves that form the hump actually have infinitely changing grade along their length, as they gradually change from a positive to a negative slope along the vertical curve. For this reason, you might want to go every 100 feet and get the grade along that length, and then you will get more of a sense of the maximum and minimum grades along a long bridge, if it is not on a straight incline or decline. 

[inkyatari]

I should have worded this better.  I should have asked, "where can I find the height data?"

[woodpusher]

Has anyone ever checked them? 
I have this gnawing suspicion that the contract called for 5% grade, so that's what the sign says. 
I saw a number of them growing up in SW Pennsylvania and then there's quite a few of them in WV as well.
It often seemed like the rise (or the fall) was more than 5%. 

[jeffandnicole]

Has anyone ever checked them? 
I have this gnawing suspicion that the contract called for 5% grade, so that's what the sign says. 
I saw a number of them growing up in SW Pennsylvania and then there's quite a few of them in WV as well.
It often seemed like the rise (or the fall) was more than 5%. 

If you locate the plans, they'll tell you the grade for every point along the roadway.

[kalvado]

Has anyone ever checked them? 
I have this gnawing suspicion that the contract called for 5% grade, so that's what the sign says. 
I saw a number of them growing up in SW Pennsylvania and then there's quite a few of them in WV as well.
It often seemed like the rise (or the fall) was more than 5%.

I would think that 5% = 2.8 deg can be done with either bubble level or smartphone app. There are quite a few apps working with built-in accelerometer...  you would also need a run of board of at least 2-3 feet long to exclude roughness. Actually once you have that piece of board and a smooth level  surface (desk, floor) you can check how that works for your tools - 5% corresponds to 1.8" height difference for 3'. Use book of about that thickness and add some paper on either end as needed.
Remember to turn your level/phone 180 deg and compare results.

[inkyatari]

Has anyone ever checked them? 
I have this gnawing suspicion that the contract called for 5% grade, so that's what the sign says. 
I saw a number of them growing up in SW Pennsylvania and then there's quite a few of them in WV as well.
It often seemed like the rise (or the fall) was more than 5%.

I would think that 5% = 2.8 deg can be done with either bubble level or smartphone app. There are quite a few apps working with built-in accelerometer...  you would also need a run of board of at least 2-3 feet long to exclude roughness. Actually once you have that piece of board and a smooth level  surface (desk, floor) you can check how that works for your tools - 5% corresponds to 1.8" height difference for 3'. Use book of about that thickness and add some paper on either end as needed.
Remember to turn your level/phone 180 deg and compare results.

Hmm.  Never thought about using my phone.  Map My Ride provides height and distance info.

[Bitmapped]

Has anyone ever checked them? 
I have this gnawing suspicion that the contract called for 5% grade, so that's what the sign says. 
I saw a number of them growing up in SW Pennsylvania and then there's quite a few of them in WV as well.
It often seemed like the rise (or the fall) was more than 5%. 

The sign that gets posted is what the bid documents (contract) call for. It's the agency putting the work out for bid's job to ensure the plans are correct.

5% grade signs are pretty common because grades less than that aren't normally steep and long enough to merit posting. I've seen plenty of signs in WV and PA for grades steeper than 5%.