Posted by David Sherman on Monday, July 30, 2007 at 14:11:31 :
Anybody have a rule of thumb for what's the steepest practical gradient for a road? I know PWs can climb trees, but I'm thinking something like 20% is more reasonable. I want to build a road between two places on my land (the highest spot on the public road and the lowest part of where I want to plant an orchard), and by my calculations the difference in elevation is 200' and the horizontal distance is about 700', which works out to a 30% grade, which seems way too steep. I know there are lots of decent logging roads with 10% grades, and most of the old CCC trails (not roads) were built at 20%, which is a comfortable pitch for walking. 30% seems awfully steep, but if it's do-able it would avoid the major hassle and mess of building a switchback on a rocky hillside. This isn't going to be a road for tourists -- just a way to get the M37 or M35 up to the flat spot to haul supplies like fencing, a water tank, trees, tools, etc. in. If I have to go with a switchback, I'd probably just make it a zig-zag one where I'd drive forward on one part and back up the other part. The hillside I'd be traversing has natural grade of about 45%.
Ideally, the grade would be gentle enough that an unloaded truck could get up it in 2WD without spinning the rear wheels. The other factor is erosion -- it needs to drain the water off the side so it doesn't become one big ugly ditch up the side of the hill.
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