The devices have been in existence since the mid-20th century, but were not popular until the 2000s because of concerns over noise. As of the 2009 MUTCD, APS are supposed to be set to be heard only 6 to 12 feet from the device to be easy to detect from a close distance but not so loud as to be intrusive to neighboring properties. Among American cities, San Francisco has one of the greatest numbers of APS-equipped intersections in the United States, with APS installed at 202 intersections . New York City has APS at 131 intersections , with 75 more intersections to be equipped every year after that.