Plus, you can't always drive slow. I was on I-40 going from Vegas to Albuquerque, and I was actually kinda scared at times. There was a vicious cross wind, blowing the semis all over the place.
And those trucks were doing 75-80. No way in heck I would let one pass me, the trailors were everywhere. I needed to get to Denver, and there was a storm on the way, so no stopping.
So, I can't really imagine going ~55mph on an interstate, even in good weather. Too dangerous.