How do I stop hyperfixating on things when driving?

I turn off or on the radio and try to focus on the lines or I'll look at the license plate and try to figure out if it says something to make it more interesting but keeping my eyes ahead

Try hitting your steering wheel each time you look at anything besides the road ahead kind of like tapping to the beat of the radio music. Hopefully the noise can bring back your focus after repeating to the point it becomes a natural reactive behavior for you. If the noise isn't enough you could try a pinch just strong enough to get you to tell yourself "hey stop that"

Try scanning the road side to side/far side of the ditch to far side of the ditch. It would give your brain a lot of information to process. Hopefully too much to hyper focus on a sign. I don't know if it'll work, but it's worth a try