Urban intersections were free-for-alls at the end of the 1800s. Traffic signals had not been invented, and reckless drivers seized the right of way. By 1900, 3 million horses, pulling an assortment of wagons and trolleys, choked U.S. city streets. The postal service moved to solve two growing concerns, transporting an increasing volume of mail into and through the cities and then delivering that mail to the addressee.
The postal service deployed several tools to move mail swiftly and securely through urban city streets.