Going 60 you need to have a _really_ good bike and want to go that fast. I barely manage to keep 30 for more than 20 minutes, and I would consider myself an average cyclist on an above average bike.

You'd need a good bike and also be an elite cyclist/sprinter. I can usually manage 30kmh for an hour or so (providing there's a good tailwind and I'm going downhill), but the issue with going faster is the air resistance which is roughly proportional to the square of velocity (rolling resistance is roughly proportional to velocity so that becomes less important). Going twice as fast will mean quadrupling your power output.