Wintergreen Ascent TT disallows cyclists going down at all. I've been down some mountains going faster than I should have, but Wintergreen is one where if you make a minor mistake you could easily end up in mortal danger (at least that was my fear at my level at the time). Also, the road isn't closed to traffic during the event which makes downhill even harder during that time. I don't think a reasonably high level cyclist would have a problem going up and down a few times in a day though, which could of course be done at any other chosen day of the year.