A railroad torpedo (called a detonator in the UK) is a signalling device used for causing a train to stop in an emergency situation. A torpedo creates a loud noise upon contact with a locomotive wheel, signaling the engineer to reduce speed to 20 mph or less; the train cannot resume its original speed until it has traveled at least 2 miles beyond where it encountered the device. Traditionally used in pairs to ensure that the sound registered with train crews, torpedoes today are essentially obsolete as modern locomotive cabs' soundproof construction renders the devices useless. Quoting from the terminology book of the Brotherhood of Railroad Signalmen:
A torpedo is a device which is strapped to the top of a rail. When a train drives over the torpedo, it emits a very loud "bang" which can be heard over the noise of the engine, and signals the engineer to stop immediately. Torpedo's are generally placed by the flagman when protecting a train ahead. Torpedoes are about 2" x 2", red, about 3/4" high, and have two lead straps attached which hold it to a rail. The torpedo has discs inside and are filled with detonating powder. The Torpedo was invented about 1874.
References
- BRS 72 - Brotherhood of Railroad Signalmen - Railroad Terminology, Slang, Definitions, quoted with permission.
