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Old December 6th, 2014, 11:36 AM   #1
Myrtonos
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MISC | Deadman equipment on trams

Can anyone here give some information on the deadman equipment on trams in your city?

It's my understanding that most of the world's trams, including the newest trams on big European legacy systems, have non-temporal deadman's controls, either classic ones where any release of the deadman's pedal or handle (or pressing the pedal right to the floor in case of the former) cuts power and applies the brakes immediately, or a system where releasing pressure first sounds and an alarms and then cuts power and applies the brakes if released for more than a few seconds. And practically no one has ever raised the slightest problem of fradulent use in case of trams.
But here in Melbourne, all three types of low floor tram have active vigilance type systems. Our Combinos were originally delivered with a non-temporal deadman's system where:

*The tram was unable to move until either the knob on the master controller or a button on the side of the armrest were pressed and held.
*If either were released while moving, a series of beeps would sound, followed soon by the aforementioned failsafe action after 5 of these beeps.
*If either were held continuously for four minutes and the tram came to a stop, a buzzer would sound and the tram would not move until the driver had released and reapplied pressure.

But soon drivers discovered that the side of the seat would hold down the armrest button if the armrest were lowered right next to the seat. The obvious solution to this would have been to have some way of disconnecting the armrest button from the deadman's braking system if the arm rest were to low (relative to the side of the seat). But when the management found out, their reaction was to modify the deadman's braking system so that the deadman's trigger have now by held continuously for no more than 1 minute before triggering a series of beeps with the automatic brakes coming on as above, and may be released for a few seconds before triggering that series of beeps with the brakes now coming on after just two of them.
Now, tram drivers practically never fall asleep at the controls, especially not when moving. If a tram driver were to do so, the chances are that they would pass through several intersections within a minute. So with a vigilance control with an interval of as long as a minute, a tram may well pass a red light or run into another tram before the automatic brakes would come on. And since neither the system retrofitted to the Combino, nor the a similiar system with which our Citadis was orginially delivered, are task linked and so it is easy for drivers to get acustomed to it and repeditively activate it in their sleep.
Now our Citadis originally have an yellow slide controller with a button on top that also had to be released and reapplied, though at much shorter intervals, leading to complaints of RSI, and increased mindlessness of the repeditive action.
Before the first of our low floor trams, all trams we had were fitted with non-temporal deadman's controls, like what our Zs, As and Bs still have. On these, there is a left foot pedal that has to be held in the mid postition when moving otherwise emergancy brake is applied, and to my knowledge no one has ever raised the slightest problem of fraudulent use. And this system responds immediately to driver blackout, quite important on tramway operations and outweighing any scope for cheating.

Vigilance control was first developed many decades ago for long haul heavy rail, where deadman's controls were found to be unsuitable, and in fact the immediate response to driver blackout is not so important here.
Vigilance control works well on heavy rail for a number of reasons, trains don't have to be steered, don't share right of way with any road vehicles, let alone pedestrians, and headways (especially in rural areas) are usually long enough that the train, even with a VC interval as long as 90 seconds, will almost invariably stop before even getting close to another should the driver fall asleep right after operating any of the controls. And the block system prevents one train from coming into contact with another without the following train passing a signal at danger, and on many railway networks, the automatic brakes will come on if a danger signal is passed. Mechanisms like train stops which brake after passing a red signal also work for heavy rail both because trains don't need to be steered (and continue to follow their tracks while braking) and because there is always an overlap beyond the signal extending to a safe braking distance from the failsafe mechanism.
Trams also don't need to be steered but tend to be driven on sight, both on street and (especially on legacy systems) on reserved track as well. As far as I know, most tram junctions, especially on newbuild systems and sometimes including crossovers, do have signals, but there is no overlap between signals and junctions.

Last edited by Myrtonos; February 28th, 2015 at 08:57 AM.
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Old December 10th, 2014, 08:46 AM   #2
lgvietnam2013
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The tram was unable to move until either the knob on the master controller or a button on the side of the armrest were pressed and held.
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