ATO brake rate

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!

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.

'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.

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.

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?

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.

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.

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!).

The lower rate is 0.55 m/s² 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/s² 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.