Speeds of London tube trains entering stations?

Question

Why is it that when a Tube normally enters a packed station it does so at great speed, but when a station is closed with nobody around they have to stick to a 5mph speed limit for the whole lenght of the platform? Doesn't make sense does it?

Answer 1

It is actually to do with signal overlaps. A train approaching a platform will normally be slowing down (for obvious reasons). But if the platform was closed and the train allowed to go through at full line speed then the trainstop equipment might not be able to stop the train in time if the station starter signal is red. The train would then be in danger of hitting whatever is being protected by the red signal, for example a set of points not properly set for that train, or perhaps even the train ahead.

The 5mph speed limit actually only applies at the station starter signal as this is approximately the speed of a departing train at this point, and the trainstop will have no difficulty in performing its job. However, drivers are instructed that, if the starter signal is red, they have to stop the train before reaching the platform and then proceed cautiously, passing the signal (once it has cleared, obviously) at 5mph.

There are exceptions to this rule. On the two automatic lines (Victoria and Central) trains enter closed platforms at normal speed as the on-board equipment is programmed to stop at every platform. When driven manually, the 5mph speed limit at the station starter still applies, but not the stopping short rule as emergency brakes wil apply if the train is too fast on approach.

Answer 2

It goes back to the Moorgate accident of 1975.

At that time, there was no speed restriction on entering stations because there should always have been a red aspect at the signal at the far end of the platform, which, it was presumed, the driver will obey. If he did not, then the automatic braking system would be activated, brining the train to a halt in the tunnel.

At the Moorgate accident, EITHER the driver ignored the signal aspect OR if the signal aspect was not at red, the driver might have forgotten where he was and continued on his way under a green (all clear) aspect. Either way, there was too short a tunnel length to halt the train before it smashed into the tunnel end. The posture of the driver's body suggested that he was not expecting a high-speed collision.

So the operating rules were changed. If the train was entering a station with only a short terminal tunnel ahead OR if the train was entering a station with a green aspect at the far end, then the speed limiters would reduce the train speed to 5mph as it entered the station.

When stations are closed, there is usually a green aspect at the platform end - hence the 5mph limit.

(If there was a red aspect, the train would have to physically stop and that would seem even more perverse to passengers on the train.)

It really does make sense!

Answer 3

Fiona is correct.

(I had a friend who, at a previous station, decided not to get on the Moorgate accident train because it was so full. She swore blind that someone told her to wait for a later train. I therefore took a lot of interest in that crash and its causes.)

Answer 4

Because when the stations are packed they are in more of a hurry to keep up the timetable

Answer 5

because we like to uphold crazy laws in this country thanks to them bast**ds at health and safety