Before revision: In many cases, modern navigational aids, including GPS, have rendered large, long-range foghorns completely unnecessary, according to the International Association of Lighthouse Authorities.Noble, D. L. Lighthouses and Keepers, Naval Institute Press, 2004, , p.169 Railway fog signals Fog signals have also been used on railway lines since the middle of the 19th century to indicate to the driver of a moving train that a broken down train, a work party, or some other unforeseen hazard is on the line ahead.
After revision: In many cases, modern navigational aids, including GPS, have rendered large, long-range foghorns completely unnecessary, according to the International Association of Lighthouse Authorities.Noble, D. L. Lighthouses and Keepers, Naval Institute Press, 2004, , p.169 Railway fog signals Fog signals have also been used on railway lines since the middle of the 19th century to indicate to warn of disabled trains, work parties, or other hazards on the line ahead.