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Post by orienteer on Aug 4, 2018 18:45:36 GMT
Are there trackside signs to let the operator know when the tail of the train has cleared a junction? I always wonder this when in the front car of an eastbound Met train joining the Circle after departing platform 3 at Baker Street, and the train doesn't speed up until clear of the junction.
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Deleted
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Post by Deleted on Aug 4, 2018 18:59:10 GMT
The speed limit signs are placed such that when the front of the train passes the new speed restriction sign, the whole of the train will be clear of the junction.
This is in contrast to how things are done on Network Rail where traction knowledge is required. But on LUL you can do it this way because of the similar or uniform length of the stock operating on each line, and maybe other things as well, like the fact tube trains accelerate quite fast so if a 7 car train starts accelerating 1 car length later than it otherwise could have it won't be the end of the world.
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Post by MoreToJack on Aug 4, 2018 22:54:35 GMT
The speed limit signs are placed such that when the front of the train passes the new speed restriction sign, the whole of the train will be clear of the junction. This is in contrast to how things are done on Network Rail where traction knowledge is required. But on LUL you can do it this way because of the similar or uniform length of the stock operating on each line, and maybe other things as well, like the fact tube trains accelerate quite fast so if a 7 car train starts accelerating 1 car length later than it otherwise could have it won't be the end of the world. Also to do with things like signal spacing etc. Essentially, because by-and-large LU is a fixed length railway it means that things can be designed around and optimised for that, unlike Network Rail where everything is designed around the longest permissible length. |
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Deleted
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Post by Deleted on Aug 4, 2018 22:56:25 GMT
The speed limit signs are placed such that when the front of the train passes the new speed restriction sign, the whole of the train will be clear of the junction. This is in contrast to how things are done on Network Rail where traction knowledge is required. But on LUL you can do it this way because of the similar or uniform length of the stock operating on each line, and maybe other things as well, like the fact tube trains accelerate quite fast so if a 7 car train starts accelerating 1 car length later than it otherwise could have it won't be the end of the world. Also to do with things like signal spacing etc. Essentially, because by-and-large LU is a fixed length railway it means that things can be designed around and optimised for that, unlike Network Rail where everything is designed around the longest permissible length.
Now how could I not think of that?   |
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Post by MoreToJack on Aug 4, 2018 23:53:30 GMT
I was quite surprised you missed that part out. Where's the real tut and what have you done with him?! 😋
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Colin
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My preserved fire engine!
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Post by Colin on Aug 5, 2018 19:46:34 GMT
unlike Network Rail where everything is designed around the longest permissible length. That's not entirely correct. All overlaps are a fixed 240 metres on National Rail. In terms of permanent speed limit signs, as on LU a decrease applies when the front of a train passes the sign. Unlike on LU though, and increase in the speed limit applies when the back of the train passes the sign.....so tut is quite correct in that knowledge of what you're driving - paticularly its length - is important. Caution speed on National Rail is 50mph - many parts of LU don't even reach that......the maximum line speed on the District line is just 45mph! That's why we'll suspend for a signal failure on the Wimbledon or Richmond branches - National Rail hate our speed control after tripping three minute time delay at 10mph!! |
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Post by bananaman on Aug 6, 2018 4:29:49 GMT
unlike Network Rail where everything is designed around the longest permissible length. That's not entirely correct. All overlaps are a fixed 240 metres on National Rail. Are they? I thought they were 200 yards (182m), rationalised in more recent times to 180m? |
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Post by phil on Aug 6, 2018 8:20:14 GMT
That's not entirely correct. All overlaps are a fixed 240 metres on National Rail. Are they? I thought they were 200 yards (182m), rationalised in more recent times to 180m? It all depends on when the signalling scheme was designed.
back in the 1960s, the standard overlap for colour light signalling (note the word 'standard' - lots of sites were different for various specific reasons) was defined by the use if Imperial measures and the figure of 200 yards was selected for various reasons.
Come the 1970s this was simply converted to metric when required - which is 183 when rounded to the nearest meter. Given the signalling design principles did not change at the time and everything was still basically geared to imperial measures (including a 200 yard overlap) nobody was particularly bothered that 183 meters was a rather curious number to use.
Through the 1980s and early 1990s the situation remained unchanged - 183m / 200 yards remained the standard overlap.
In more recent decades however this British Rail legacy has been challenged and as with many things new standards have been adopted.
There is no requirement to apply the new standards retrospectively (unless layout changes etc require a partial resignalling, in which case all new work will be done to the latest standards)
As such I believe recently installed and forthcoming schemes now use the figure of 240 meters as the length of the 'standard' overlap - which is all worked out on a totally metric basis and no doubt produces a rather odd figure if quoted in yards .
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Deleted
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Post by Deleted on Aug 6, 2018 9:27:14 GMT
240 metres - 262.465 yards
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