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| Re: What exactly is a signal problem? (1403923) | |||
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Re: What exactly is a signal problem? |
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Posted by gbs on Sun Jul 31 00:37:27 2016, in response to Re: What exactly is a signal problem?, posted by AlM on Sat Jul 30 15:51:23 2016. The t/o was "keying by" the signal, under proper authorization. Every automatic signal has a joint in the rail about 15 feet before it, and when the wheels of a train cross that joint the stop arm goes down, allowing the train to pass without tripping the brakes. This must be done at a very slow speed to give the arm time to go down after the wheel crosses the joint. Every safety system installed (either on the trains or on the tracks) is designed to stop trains or prevent them from starting, but each system must be able to be over-ridden or bypassed (always with proper authority), because a stuck train completely ruins service and must be moved out of the way. Examples: 1) the brakes on the train are essential to stop the train, but if they get stuck and don't release, the train can't move, so the brakes can be cut out if necessary. 2) the stop arm prevents collisions by preventing trains from getting too close to each other, but if an arm gets stuck in the up position, service stops, so trains can key-by. 3) trains can't start until the doors are all closed and locked and indication is passed to the t/o, but if indication is not passed for some reason and it can't be corrected en route, then indication can be by-passed and the train can move. Generally when these over-rides occur the train is taken out of passenger service, but at least it can be moved out of the way. |
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