Michigan's state and local road agencies follow the standards published by the American Association of State Highway and Transportation Officials (AASHTO) in "A Guide for Erecting Mailboxes on Highways."
- Only one support should be used per box or group of boxes;
- Wood posts should be no more than 4 1/2 inches diameter if round, 4x4 inches if rectangular;
- Metal pipes should be standard steel or aluminum with no more than a 2 inch inside diameter;
- Supports should yield or collapse if struck. They should bend or fall away from a vehicle and not create a severe deceleration;
- Supports cannot be fitted with an anchor plate (metal post), embedded over 24 inches into the ground, or set in concrete;
- The mailbox must be constructed of sheet metal, plastic or similar weight materials, with weight not to exceed 11 pounds;
- The United States Postal Service asks that roadside mailboxes be 36 to 42 inches off of the ground, and 8 to 12 inches behind the shoulder or the curb;
- A mailbox and its support will be considered hazardous to motorists when the support exceeds the described structural imitations; and
- Any mailbox and its support considered to be a hazard should be removed from the road right-of-way and replaced.
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