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Post by cobolot5 on Nov 7, 2021 7:30:06 GMT
I've noticed that in ATO the brakes are applied earlier at Snaresbrook eastbound. Is this because of leaf fall? Are the brake rates infinitely variable or are there set rates? I guess the previous station's PAC sets the brake rate? Is this easily changed from Wood Lane? Or does it require a trip to the SER to change the EPROM? Thanks for your advance from an inquisitive user!
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Tom
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Post by Tom on Nov 7, 2021 15:34:51 GMT
The previous station's PAC (Platform ATO Communicator) does have a default brake rate value, but these can be varied from the Control Centre. I'm not sure how much variation is available but I do know that brake rates are changed in the Autumn to counteract adhesion issues.
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Post by Deleted on Nov 7, 2021 17:36:02 GMT
I've noticed that in ATO the brakes are applied earlier at Snaresbrook eastbound. Is this because of leaf fall? Are the brake rates infinitely variable or are there set rates? I guess the previous station's PAC sets the brake rate? Is this easily changed from Wood Lane? Or does it require a trip to the SER to change the EPROM? Thanks for your advance from an inquisitive user! As far as I am aware, Leytonstone - Snaresbrook (eastbound) has a 65kmh speed limit. Snaresbrook - Leytonstone (westbound) also has a 65kmh speed limit. However, as you approach the junctions at Leytonstone, ATO brakes down to 55kmh. Hope this helps! |
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Post by capitalomnibus on Nov 8, 2021 16:02:49 GMT
I've noticed that in ATO the brakes are applied earlier at Snaresbrook eastbound. Is this because of leaf fall? Are the brake rates infinitely variable or are there set rates? I guess the previous station's PAC sets the brake rate? Is this easily changed from Wood Lane? Or does it require a trip to the SER to change the EPROM? Thanks for your advance from an inquisitive user! As far as I am aware, Leytonstone - Snaresbrook (eastbound) has a 65kmh speed limit. Snaresbrook - Leytonstone (westbound) also has a 65kmh speed limit. However, as you approach the junctions at Leytonstone, ATO brakes down to 55kmh. Hope this helps! 65 Km/h is practically 40 Mph, that is a bit slow. I would have thought the train could easily achieve 50 on some of that stretch. They do seem to go some insane speed between Leytonstone and Leyton which seems like it is around 55-60mph. |
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Post by Deleted on Nov 8, 2021 19:55:07 GMT
As far as I am aware, Leytonstone - Snaresbrook (eastbound) has a 65kmh speed limit. Snaresbrook - Leytonstone (westbound) also has a 65kmh speed limit. However, as you approach the junctions at Leytonstone, ATO brakes down to 55kmh. Hope this helps! 65 Km/h is practically 40 Mph, that is a bit slow. I would have thought the train could easily achieve 50 on some of that stretch. They do seem to go some insane speed between Leytonstone and Leyton which seems like it is around 55-60mph. I know - I believe they are at a target speed of 65kmh because of the bend. The normal target speed out of the tunnel is 85KMH. |
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Post by spsmiler on Nov 8, 2021 20:20:51 GMT
65 Km/h is practically 40 Mph, that is a bit slow. I would have thought the train could easily achieve 50 on some of that stretch. They do seem to go some insane speed between Leytonstone and Leyton which seems like it is around 55-60mph. I enjoy looking out the window and seeing if the train is keeping up with the traffic between Leytonstone and Leyton. That said, in the evenings - when the road is busy - the traffic is slow and eastbound trains almost always fly past the road traffic. |
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Tom
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Post by Tom on Nov 8, 2021 22:35:06 GMT
The normal target speed out of the tunnel is 85KMH. 'Normal' target speed depends on a variety of factors, such as track condition, geography, status of track circuits and signals ahead. There is no generic 'normal' target speed either in tunnel or outside, but there are a series of speeds which the different track circuit modulation codes reflect. Maximum permitted speeds on the Central line in certain sections can be as high as 100km/h with no trains around and clear signals; the 85km/h is set by the ATO controllers on the train following the 2003 Chancery Lane derailment and it is quite possible to drive in Coded Manual in excess of this speed. Please bear in mind that this thread is related to ATO Brake rates rather than speeds, and the question has been answered. If you have further to contribute relating to brake rates, please do so, but if you wish to discuss speeds on different sections of line and the factors associated with them, please do so in a new thread. |
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Post by cobolot5 on Nov 11, 2021 3:37:12 GMT
Thanks all for the info. I'm lead to believe because of the brake rate changes between underground and surface, stations like mile end can't be skipped in ATO?
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vincenture
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Post by vincenture on Nov 11, 2021 4:26:58 GMT
I've only heard of leaf fall restrictions on the Piccadilly and Metropolitan lines. The brake rates aboveground seem to be slightly slower compared to back then but I may be wrong.
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Tom
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Post by Tom on Nov 11, 2021 16:25:36 GMT
Thanks all for the info. I'm lead to believe because of the brake rate changes between underground and surface, stations like mile end can't be skipped in ATO? That's correct - last station before leaving the tunnel cannot be station skipped. The affected stations are Shepherd's Bush WB, Mile End EB, Wanstead OR, Gants Hill IR. |
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Post by cobolot5 on Nov 14, 2021 6:41:57 GMT
A further ATO related question. Sometimes when the train emergency brakes in auto, I guess when it doesn't meet the new target speed/mss. I thought that the train couldn't continue in auto. But after a trip the other day the train was definitely restarted in auto. Similar with leaning on doors after a while the operator may apply the brakes. I thought that after interrupting ATO by knocking the tbc it wouldn't allow you to restow and press start again and continue?
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class411
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Post by class411 on Nov 14, 2021 9:38:13 GMT
Thanks all for the info. I'm lead to believe because of the brake rate changes between underground and surface, stations like mile end can't be skipped in ATO? That's correct - last station before leaving the tunnel cannot be station skipped. The affected stations are Shepherd's Bush WB, Mile End EB, Wanstead OR, Gants Hill IR. There must be a very good reason for that. Does anyone know what it is? And does the same rule apply to any other lines. |
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Tom
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Post by Tom on Nov 14, 2021 16:45:30 GMT
Just the Central line to the best of my knowledge.
When the train stops at a station it receives its route and run data to the next three stations, and part of that data is the brake rate (more accurately the deceleration rate) to use in calculating when to brake.
The surface brake rate is different to (and more importantly, less than) the tunnel brake rate, because the rails can't be guaranteed to be dry and the coefficient of friction is lower. Similar to driving a car, it takes longer to stop in the wet!
If the last station before the tunnel were to be skipped it means the train is leaving the tunnel using a tunnel brake rate which means the train will brake later than it should, but because the friction coefficient is lower outside you can't achieve the brake rate required (and you can't stop in the distance available) - which increases the risk of a SPAD.
For that reason, if the last station before leaving the tunnel has to be non-stopped it needs to be done in Coded Manual.
When Shepherd's Bush was closed in 2008, we modified the brake rate at Holland Park to permit Shepherd's Bush to be skipped, as there isn't a safety issue arising from using a surface brake rate in the tunnel. You arguably get a slightly lower throughput as trains are braking more gently, but this was offset by the fact that there was no longer any dwell time at Shepherd's Bush to adversely affect headway.
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Post by zbang on Nov 14, 2021 17:29:58 GMT
I'm a little confused here-
If the train gets info for the next three stations, wouldn't that include the decel info coming into each station separately? I assume that the three-station-info is so that if data isn't picked up at a stop the train has enough to go on to the next where it might.
Maybe a better question, which would be a digression, is what's contained in those data blobs and why it contains multiple stops.
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Tom
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Post by Tom on Nov 14, 2021 18:10:28 GMT
No, it doesn't. From memory there are two bits of deceleration info, one for a target speed reduction and the second for a station stop. But they're generic and not specific to each potential stopping or braking location.
To explain the three station rationale: When the contract was let, Chancery Lane routinely closed on Sundays and Fairlop was closed on both Saturdays and Sundays. The idea was that you had to have data to get you to the next station, and then if that was closed to at least one more. However, as the line had stations that were routinely closed at the time, the data had to support two consecutive closed stations.
It might also have had something to do with the Hainault to Woodford service finishing at 2000 each evening, so an ATO train running to Hainault depot could depart Woodford in ATO, skip Roding Valley and Chigwell, and stop at Grange Hill ready to enter the depot (which could only be done in manual), thereby reducing the workload on the Train Operator.
I 'm not going to go into the specifics of the data, but suffice to say it contains a map of the railway written in the appropriate programming language, which includes signal and block marker positions and stopping locations in platforms.
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Post by 100andthirty on Nov 14, 2021 22:36:30 GMT
If I recall correctly, there are three nominal service brake rates, a higher rate for tunnels at, from memory, 1.05m/s2 for tunnel, 0.75m/s2 for open running with a lower circa 0.6m/s2 rate for autumn. As I understand it, but could well be wrong, the choice of open brake rates can be selected from the control room.
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Tom
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Post by Tom on Nov 14, 2021 23:14:16 GMT
Definitely the 0.75m/s2 outside, I think it was 1.15 in the tunnel. All brake rates can be selected from the Control Room from memory (going back to the days of Shepherd's Bush again!).
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vincenture
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Post by vincenture on Nov 15, 2021 6:29:42 GMT
1.15 is pretty quick, no wonder the last underground station cannot be skipped
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Post by d7666 on Nov 15, 2021 15:57:06 GMT
Definitely the 0.75m/s 2 outside, I think it was 1.15 in the tunnel. All brake rates can be selected from the Control Room from memory (going back to the days of Shepherd's Bush again!). The lower rate is 0.55 m/s 2 on poor adhesion advice [from ACCAT] is available IIRC; implemented ~2011 or so, been in use for a while now. I think I have seen docs that did once state 0.6 m/s 2 was the lowest appropriate for ATO but things moved since then in the field of SPAD mitigation etc. Once again it is some time since I been at Wood Lane, things may have changed further since. |
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Post by cobolot5 on Dec 9, 2021 4:25:38 GMT
Does anybody know why Wanstead inner rail has a brake rate similar to surface stations? I would have thought at Leytonstone the PAC would upload a tunnel brake rate similar to at Stratford WB to mile end.
I could be wrong but the brake rate at wanstead inner rail definitely doesn't feel a sharp as other tunnel stations
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