Many states issue orders specifying the designed warning time at each crossing. The Federal Railroad Administration minimum warning time is 20 seconds. The goal is to give adequate warning, but not too much time that would encourage motorists to disregard the signal. Many modern crossing signals have "constant warning" technology which not only allows for the warning time, but adjusts to the speed of the oncoming train to give the same amount of warning, regardless of whether or not the train is moving slowly or very rapidly. At some crossings, a "cantilever" extends out above the street with additional flashing lights to warn motorists in multi-lane situations. Most crossing gates are designed to warn against motor traffic in the oncoming lanes, covering half the street, allowing an escape from the tracks for motorists who happen to be on the crossing when the signal is activated. Each one is custom designed to fit a specific need. Today the basic designs come in a wide variety of configurations, depending on the complexity of the street crossing and the railroad. The first flashing red light signal was installed in New Jersey in 1913. The wig wags gave way to the alternating flashing red lights mounted as part of a cross-buck sign, often used with gates as well. Such "automatic flagmen" signals were soon dubbed "wig wags." A few wig wags remain in use today in the United States, much beloved by railfans for their nostalgic warning. The electric bell idea quickly was expanded to include a swinging round sign with a red light hanging from an arm on the signal pole to simulate a flagman waving a red lantern. When the electricity was diverted through the train – which was a path of lower resistance – instead of the relay connection, the contacts connected and the bell rang. The current flowed through the steel wheels and axles of the train, cutting off (short-circuiting) electricity to an electrical relay which needed the power to hold the electrical connection apart that kept the bell off. They were activated when a train entered a circuit where the rails were insulated to confine the electric current to a designated piece of track. The first automatic crossing signals were bells mounted atop poles. The design formed the basic sign still in use today. The Stalwart Safety Sentinels of the Roadīy the 20th century, the use of "cross-buck" signs – the boards forming an "x" – were common. Some of the crossings were equipped with gates that the watchmen manually cranked to lower or to raise.Īs it wasn't practical to have people stationed at all the crossings, a way was sought to automatically alert the public that a train was approaching. Initially, a colorful variety of signs were posted at crossings, depending on the whims of the local railroads, and in time, watchmen were stationed at the busier crossings to warn of approaching trains. By dividing the railroad into "blocks" or sections, a circuit was devised to signal trains when a specific section of track was clear or occupied with other trains.Īs America became laced with more railroads in the latter half of the 19th century, it became apparent that warning also should be given to people who wanted to cross the tracks. The idea of using electric current in railroad rails for signaling was an idea that had been suggested as early as 1848. The basic technology goes back to 1870 when the track circuit was invented. How they originated is an interesting story. They are highway-rail grade crossing warning systems. Uniquely American, they are common, highly sought after, and work through seemingly mysterious, but time-tested science. Rail Crossing Warning Systems The Stalwart Safety Sentinels of the Road
0 kommentar(er)
