Upvote:4
Is this a safety thing, and backing out of a tollbooth is particularly dangerous?
Yes. Oncoming drivers may not notice that you are backing up, thereby judging their stopping distance incorrectly, increasing the chance that they will collide with you.
Is this a legal thing? (e.g. perhaps cars are considered legally impounded upon reaching the tollbooth and the government requires payment to legally "release" the car, so backing up constitutes an attempt to evade a legal impound).
Not as far as I am aware.
Is this mostly a tradition or done for historical reasons?
Safety measures are usually implemented for historical reasons. I suspect that before these signs were in use, people backing up at toll booths were identified as a cause of preventable vehicle collisions, but I do not know this for certain.
Is this done for some other reason?
Not as far as I am aware.
If you can't find your money or toll tag. Instead of sitting there blocking the toll lane searching under the seat for loose coins, you could back up and park on the side of the road and do it.
Another reason for backing up: you've entered the wrong lane and want to correct the problem by going to a different lane. Some lanes accept payment only with an RFID tag, for example. If you drive into that lane without one, what do you do? Many people would first think of backing out of the lane.