The guy would be in the area for a week or two prepping for a race at Park City. His training at that time of the season was all on the road. A couple of the rides he did took him out Provo Canyon and I was quite worried that he did his ride on the highway. I asked him how he handled the tunnel and asked if he had a mirror on his helmet to watch approaching cars from behind. He said that mirrors were actually a problem because the act of looking at it pulls you to the left a bit. His strategy was to keep his vision straight ahead, stay as far right as the road condition would allow, and go as fast as possible. I guess you have to be somewhat crazy to be a professional mountain biker so his taking risks on the highways is consistent.
Unrelated tidbit....On his "power training day" he road up Squaw Peak Road 10 times in the highest gear, while staying seated in the saddle. Needless to say, he had rather powerful quads.