Well.. I do agree with Rob Steven.
Most of alpine snowboarding accidents happens when we make a wide arc to a direction, which will cross almost entire (or at least significant amount) width of trail.
Let's compare it with a driving a car. On 6 lane highway, I'm cruising 55 mph on far left lane at 4 a.m. A ferrari is on the far right lane, just ahead of me, switching lane back and forth constantly (far right and one that next) at 55 mph. Suddenly the ferrari crosses all lanes and hits my right side. Whose fault is that? The Ferrari driver will get a reckless ticket and bills from my insurance company that claims my necks, spine, other crap I decide to claim, and repair cost of my Tico, which will be just about same cost of his fog lamp repair. :)
I had an accident early last season that I was downhill rider. In order to get away from a obstacle, I had to cut cross the trail and hit a 5 years old girl who was coming straight down. She got thrown forward good 15 feet. Luckly, her parent knows Skier's codes and apologized to me. Although I was a downhill rider, she was good 30-40 feet away from me. I should look uphill before I make that turn. I quit riding right after the accident and went home for that day. The skier's code covered my ass but as I think of it every time, it was my fault. I don't think she or anyone could get away without collision because I know how tight and sudden the turn was... and I don't think I could call myself as a downhill rider at the moment.
We should look up as much as we can....