We do it on roads that we know there is a road on my way to school that is 2 lanes each way with a turning strip in the middle. Busy as hell. It has the smooth seal (the smoothest you can get) for about 2 or 3 km, and there are no obstructions. I know it well. I draft trucks and buses at over 50kmh uphill along there! I once moved off from the lights behind a bus though, but flagged drafting it as soon as the water started running off the back of the thing! This is on the MTB too, not the roadie!

Brendon