Traffic Law Updater

All traffic laws, including local ordinances, in a given nation should be written in a standardized format. All villages, cities, towns, counties, states, etc. would have a booth, like a tollbooth, at each entry point at their borders. As you drive through, you come to a stop and a dash mounted module in your car retrieves information from the booth with a list of every traffic law in that town that differs from your hometown (this is why the codes must be standardized, to aid in the cross-referencing). All local laws which differ from those in your hometown are displayed on a digital readout, or printed on a paper receipt for record keeping. This allows you to enter a town with all the knowledge you need to avoid running afoul of the local authorities. Stop, download, pullover, peruse, resume.

Use of the booths and installation of the dash unit would be entirely optional, but then if you choose not to use it you waive your right to plea ignorant in the event that you do get pulled over for a traffic violation. I.e., if you're found guilty, and your only excuse is ignorance, you will pay the fine.

Either that, or simply a large sign at every border crossing with a complete list of all local traffic laws, and a small parking lot, like a typical highway rest stop.

Again, take your pick.