I've ridden on the highways here w/ no traffic. It's a blast. The 5 boro bike tour and the MS ride both close down highways around NYC for riders so all you see around you are cyclists taking up all the lanes on the highway. And we still get backed up at the hills.

I dunno about riding the highways when traffic is moving at 75-80 mph though. There are some terrible drivers out there who tend to drift into the breakdown lanes cuz they're not paying attention or they just can't drive.