It just seems so backwards that making a concrete mailbox can get you sued by a jerk that intentionally drove into it. I can understand banning pitfalls and other actual traps, but why passive defensive deterrents? After all, it’s not like a bystander accidentally wandering onto your property is going to be injured by a random bolder you placed between your garden and the street.
(Edit): It seems I had a fundamental misunderstanding of US law. Thanks for indulging my curiosity!
The concrete mailbox ban isn’t there due to a booby trap ban.
There are a lot of regulations regarding what can be near roads as their presence can provide a potential hazard to traffic. This includes a mailbox. Mailboxes are designed to be within the clear zone, the area that needs to be kept clear of obstacles, in order to allow mailmen to deliver mail to them. So, in order for them to be within the clear zone, they have to be designed to break away when hit by a car.
This has nothing to do with the intent of the person hitting the mailbox.