This is the context:
"The Great Divide route is a network of lost mountain passes and valleys that are traversed by a patchwork quilt of forest service roads and trails and four wheeler roads and double tracks."
It's about a mountain bike race from a city in Canada to the boarder of Mexico.
Ah, in that case I think that you should be looking at "four wheeler(s)", not "wheeler roads. I imagine that these are roads that are only suitable for vehicles with four-wheel drive, but maybe someone else will be able to confirm that.