Speed od Signal Changing

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Speed od Signal Changing

Post by sstockfan on Sat May 05, 2012 11:02 am

In my opinion, the signal changing from green/yellow to red when the train passes is so quick. In real life in the UK. It doesn't change that fast when the first carriage is past the signal. In some cases, the signal doesn't even change until after the whole train is gone. What's your opinion?

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Re: Speed od Signal Changing

Post by graymac on Sat May 05, 2012 1:18 pm

Modern signalling systems are responsive in the way the sim acts. Certainly here in Ireland.
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Re: Speed od Signal Changing

Post by pedned on Sat May 05, 2012 11:24 pm

graymac wrote:Modern signalling systems are responsive in the way the sim acts. Certainly here in Ireland.
It depends where the track circuit starts/ends. Sometimes the next circuit may not be until a train length after the signal, but that is usually the maximum distance between. Normally it's around a coach length.

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Re: Speed od Signal Changing

Post by Quork on Sun May 06, 2012 12:50 am

In Germany, the situation is as follows:

==Γ==·=======Γ==·=======Γ==·=====

The Γ are signals (in this case, signal and distant signal in one place, be it combined H/V signals light (not talking about semaphores as they are often thrown back manually), be it main signals with presignal functionality in the Hl, Ks or Sk system), the · marks the spot where the axle counter is. The distance between signal and axle counter is at least long enough to make sure the leading vehicle's PZB antenna (the PZB of not leading vehicles is either disconnected or off (yeah, that's a big difference)) has passed the trackside PZB antenna safely, so let's say 20m, and gets to as much as 300m. Therefore depending on the place the reaction time can vary from nearly immediate reaction to quiet some time.

Let's talk in examples. The train travels from left to right. It passes the first signal showing Hp1 (free) and Vr1 (expect free). After the first axle reaches the axle counter, the signal is thrown back to Hp0 (stop) (the distant signal is dark then). The axle counter counts how many axles the train has. The train travels further, it passes the second signal, which, again, is showing Hp1 and Vr1. Some seconds later, it reaches the axle counter of the second signal. The first axle makes the second signal drop back to Hp0. The first signal still shows Hp0. The train continues, and when the axle counter has counted as many axles as the first one, the first signal rises to Hp1 again, while the distant signal shows Vr0 (expect stop) as the second signal is on stop now. I think you get the clue. With track circuits, which are a rather historical (though still common) technology here, it's the same. The deciding point is up to 300m behind the signal.

That 300m thing leads to a rule about going on sight (going on sight means you are going with max. 40km/h (clear day)/15km/h (clear night or tunnel)/5km/h (in mist), but slow enough to be able to stop before any disturbance, be it a vehicle, be it a track defect, etc.) in the case you go on sight from signal to signal: If you get signal Zs7 (pass signal Hp0 or defective light signal without written order, continue on sight) or you get order 9 (You are going at max. ...km/h / on sight from ... to ...) to go on sight from a signal to a signal, you have to continue going on sight for 400 more metres behind the signal the order ends on. I'll explain on the above-mentioned example.

Let's say the train loses a carriage. This is highly unprobable, but it happens. Now let's further assume, the train doesn't automatically stop. This is virtually impossible, but that's what railway regulations are all about; ensure safety even in the most unprobable case. So, the carriage comes to a stop behind the second signal but just before the axle counter. Because of that, the second axle counter doesn't count as many axles as the first one, leading to the first signal staying on Hp0. However, the rest of the train continues and passes the third signal and its axle counter. That one counts the same amount of axles as the counter behind the second signal, leading to the second signal going to Hp1. Now, a following train stands in front of the first signal. The signalman sees on his table, that the first train has already passed the third signal; so he assumes the red lighting of the track depiction between signal 1 and 2 on his table (that's the occupancy indication) to be a defect. So he dictates an order to the train driver of the second train; order 2 to pass the signal 1 and order 9 to go on sight from signal 1 to signal 2, and the reason code for "track might be occupied". So the second train passes the first signal, goes on sight and reaches the second signal. The second signal shows Hp1, as explained before; but would the train accelerate now, it could have reached quite a high speed before reaching the axle counter and the carriage standing just short of it, leading to a crash. But just to prevent that scenario, we have that 400m-rule I mentioned. The train has passed the signal 2, continues on sight for another 400m and thus comes to a safe stop in front of the runaway carriage. (Why 400m when the maximum distance to the signal is 300m? Due to the kilometration signs standing 200m apart that's easier to execute, and it's a safety margin)

Now, under those circumstances, one might ask, why not simply build the axle counters in a small distance, why keep up to 300m? You have to remember there is something called the overlap, and this has to be kept clear, too. If the axle counter, for throwing the signal back to Hp0, would be just behind the signal to prevent the scenario of a vehicle between signal showing a free aspect and axle counter, you'd still need to keep the overlap observed, so you'd need a second axle counter at the end of the overlap. That would mean two counters instead of one; that's twice as many devices to build and maintain, that's twice as many possible sources of defects, and that's one more thing complicating signalling construction one more step. In sum, the current solution of only one axle counter, at the end of the overlap, is safer, more economic and easier.
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Re: Speed od Signal Changing

Post by Greater Anglia Metro on Tue May 08, 2012 10:00 am

Stonebridge Park southbound is a good example of this, I have a video somewhere of a class 508 leaving, and the signal not going back to red for a good half mile past the signal...
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