Today I rode accross the newly built Carquinez bridge near Vallejo CA. There's a walkway/bikeway that parallels the freeway offramp -- a long, downward sloping, curving stretch of about 1/4 mile.
While it's made of concrete, it seems they've covered it with a nice, patchy layer of gravel.
My guess is that the gravel is so that pedestrians don't slip and fall when it's wet. What I don't think they realized is how dangerous this is to cyclisits. I may be wrong, but wouln't a good squeeze of my brakes cause both wheels skid?