> The only way I avoid it is to be constantly scanning by moving my eyes around - side mirror, rear mirror, speed gauge, back to the road. Delay(5s). Repeat.

I'd add an occasional glance at the horizon too , if you're on a long trip. You can make it a game if you're driving a new route (guess which mountain is closest to the road you're on) Frequently changing focal distance helps a lot to prevent eye fatigue.