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Sloooooooow Trains

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  • 25-08-2006 8:50am
    #1
    pleba
    Closed Accounts Posts: 119 ✭✭


    It's possible this has been asked before and there is a perfectly reasonable explanation, but I was wondering if anyone knows why 100% of the time between Dublin Connolly and near Killester trains slow right down, sometimes almost coming to a complete stop


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    #2
    MarkoP11
    Closed Accounts Posts: 1,331 ✭✭✭MarkoP11


    Its called a red signal, the system is dealing with more trains than it was designed for, it really depends on the time of day. There is a 20/30mph limit from East Wall into Connolly and 30mph to Pearse its 70mph northside, 60mph southside

    If you are on a DART the onboard computer system will inforce strict speed limits when faced with anything other than a green signal so approaching a red signal about 300m away from it the computer will intervene and bring the speed down to little more than a walking pace, if you sit in the front coach you will hear a beeping noise indicating the next signal is red or a continuous tone to indicate the computer is in control and is inforcing a speed limit

    If the driver doesn't react (by selecting at least neutral) or the brakes don't apply with sufficient strength the computer will force a immediate emergency stop, had that twice this morning due to the rain


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    #3
    loyatemu
    Registered Users Posts: 14,782 ✭✭✭✭loyatemu


    ok heres a similar question.

    Darts coming to a complete halt where there is no signal, then immediately starting to move again. Happens occasionally between Greystones and Bray, but also elsewhere on the line. Whats the cause?


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    #4
    MarkoP11
    Closed Accounts Posts: 1,331 ✭✭✭MarkoP11


    If the driver exceeds the speed limit presented by the computer the computer steps in and applies the brakes until such time as the speed falls below the permitted level if the brakes don't apply with sufficient strength the computer will force a immediate emergency stop. If the driver doesn't select brake or neutral in recognition of the speed request the train stops. The driver need only select neutral, the computer system will apply the brakes

    There is a decelerometer which detects the rate of deceleration, if the train slides or the anti lock brakes trigger excessively the train might not achieve the required 10-12%g braking rate the computer sees this as a critical fault since it would then mean the train could no longer meet the braking distance requirements to ensure safety. Needless to say the decelerometer circuit and brakes have given trouble since day one


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    #5
    Cerdito
    Registered Users Posts: 365 ✭✭Cerdito


    With the control that the computer has, as outlined above, you'd have to wonder if a driver is needed at all.

    I was on the underground in Copenhagen, the trains have no drivers at all. Kind of spooky sitting right up the front of the train looking straight out the front window.


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    #6
    Snivilian
    Closed Accounts Posts: 47 ✭Snivilian


    Tell me, with all that technology why do we need train drivers


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    #7
    Chris_533976
    Closed Accounts Posts: 3,082 ✭✭✭Chris_533976


    Failsafe. If the computer screws up, a human will always be able to analyze a situation whereas a computer cant.


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    #8
    MarkoP11
    Closed Accounts Posts: 1,331 ✭✭✭MarkoP11


    There is a spare slot in an equipment cabinet to permit the later installation of automatic train operation, in fact some of the clever features are not available while being driven in manual, the PR from the manufactures, GEC clearly states "during the initial manual driving phase" blah blah are not available

    The computer is really really dumb it has one simple equation to solve

    while(current speed greater than permitted speed)
    apply brake
    if(controller powered or brake rate too low)
    stop

    The system is failsafe in the sense if the computer loses the code stream from the track it assumes red and stops, disabling the system results in the computer doing a phone home to log the event even then you are stuck at 30kph

    Every time the drivers threaten a strike I love to bring this up but you still need someone present to stop the train when someone jumps in front of it, local vandals block the line, fallen tree etc


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