It wasn't a restriction. It is State Law because I live off a State Highway. A 70mph highway at the time. It was lowered to 60mph after it was widened.

I'm pretty sure all state and federal roads have break away sign post requirements. I've seen many downed road signs on I-35. Either from sleepy truck drivers or the wind. My state road intersects I-35 about 3.5 miles from me. Someone took out a stop sign down there a few days ago.
USPS has regulations on mailboxes. Not sure about the post but for sure a minimum and maximum height of the box itself. I'm in a rural area. They deliver mail by reaching out of the vehicle and putting it in the mailbox. And yes, on that 60mph highway.
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