No. Its maybe possible to have a sharp edge on gravel. But not likely. Gravel on roads in the USA are made from limestone. Its a very soft rock. Easily crushed and easily rounded by use. Gravel roads in the US are not made out of granite that can hold a sharp edge.
Not no, just maybe. Most roads in the US are made of the cheapest rock that's available within 30-60 miles. Usually that ends up being limestone, but not always.
The railroad beds you are talking about are not made from limestone like gravel roads. Railroads use a different rock of much larger size for the track beds. You will never see this rock on gravel roads or trails in the US.
Most railroads I know of ARE ballasted with limestone, it's just a much larger size. There's one rail-trail that's barely rideable with standard MTB tires, because it does use the railroad ballast as the surface. It's maybe 2-3" screen. Horse riders don't mind it too much, though.
Also, some fire roads, at least in the southern Appalachians, that have been covered in gravel use large screen rock. It doesn't USUALLY approach railroad gravel size, but again, where the road managers have to deal with severe erosion, there are exceptions. 1/2" gravel washed? Put in 1". 1" washed out? Try 2".