Yes on what David wrote. I've even competed in or coached in races where there was a course option. As long as the race lets the competitors know in advance there is an option I think that's a cool race idea. The race I did was an XC ski race where you could choose to take a straighter path that went up and down a big hill or you could take a slightly longer path that avoided the hill. Most of the field took the slightly longer path.
And to Mark regarding has a train ever been stopped from going where it wanted to go by a race... In the early days of the marathon I work for our Course Director parked his truck across the tracks after a train that we were assured would not be operating during the race started crossing our course to attached cars. The train was crossing onto the course then moving off, so during one of the gaps he moved his truck in. The RR was not pleased, but we had the paperwork to back up our actions and they didn't push things.