You can use arrow keys to navigate in the map.
Road signs, like speed, exits, or information are basically the same as billboards and they do not cause accidents. It is also fairly easy to tune out billboards anyways.
Thinking out and typing a message takes more time on average than glancing at a sentence and comprehending what you read in most cases.
Not all vehicle occupants are drivers, so billboards would pose no threat to their safety. Some vehicles do not even require drivers.
The point of billboards are to get your attention.
If the point of billboards is to ''get your attention'', than it is simply a distraction from the road.
A distraction will cause one to be at more risk to accidents on the road.
Anything that distracts you and causes you to be at more risk of a crash should be illegal.