ATO

To answer your initial question as a driver, I think its a very good system overall. While it is a fixed block system that works in a station to station nature, the proximity between trains is not far off what you’d get with TBTC for comparison.

To some extent it still works to the same principles as conventional signalling for example categories of signal, shunt signals etc. This means the Rules and Procedures training is not totally alien to someone coming in as a new driver from Ashfield House (you have to learn conventional signalling first regardless of what line your going to) or transferring from another line.

There is also more scope to operate under degraded conditions without impacting the service too much and Coded Manual mode is far more user friendly than what I’ve seen of Protected Manual mode in TBTC.

Without looking at a spreadsheet of reliability I’d say its reliable, the most common issues in my experience are temperamental train bourne issues that require a “trip and reset” of the ATP.

Huffing and puffing trains coming up in a heap is 99.9% of the time down to low rail adhesion, and the sound is the Wheel Slide Protection system kicking in.

www.davros.org/rail/signalling/articles/central.html
This site gives a good overview of the system with all the relevant dates.

My experience of travelling on the central line as a passenger over the years is that the ATO doesn't perform very well in wet weather, with the trains stopping short or stopping between stations in the open sections (I recall somebody telling me once that it was related to the number of wheel turns not matching what the train would expect for a given distance travelled, causing the train to stop). It doesn't make a huge difference to the time it takes to complete my journey, but given rain is not uncommon, it seems a bit of design limitation (and coming to a sudden halt in wet, low adhesion conditions can't be good for the wheels!).

One particular highlight is that it seems to be 'sensible' in its design, allowing trains to get quite close to one another (for example, the closest I have ever seen two moving trains allowed to get is at Woodford, when a Hainault train is crossing over onto the eastbound platform from the siding [? the siding is called 21 road] and at the same time a westbound train is entering the westbound platform - at a cautious speed. I suspect on a more modern ATO system the westbound train would be held outside the platform until the Hainault train had crossed over onto the eastbound.

Another highlight from my perspective is that the LED next train indicator boards always seem accurate, and often give more accurate information then platform staff especially at times of disruption when there are last minutes changes. I also like the ability of the boards to display 'held' next to the destination although I'm not sure what triggers this.

"Held" means that the train is currently not moving, often for longer than usual. It is expected that it will continue its journey, but the signalling system doesn't know how long the wait will be. The most common reasons are either because it's waiting at a red signal (or equivalent) or the driver has been instructed to wait in the platform so the train isn't stationary between stations for an extended period.
Or, alternatively

The control centre can hold a train in the platform via the ATO system - this comes up as 'Held' on the Train Operator's desk. It may well (I've never read into it that much) also cause the Dot Matrix Indicators to show held.

I tend to agree with class411 that 'held' doesn't really make much sense to someone watching the Dot Matrix several stations down the line. Maybe 'delayed' would be a better term.

Driving CM in low rail adhesion requires lighter, earlier braking in order let the Wheel Slide Protection work effectively. ATO can get it right sometimes, and I know Wood Lane SCC can implement a lower braking rate on the open sections as they do in the leaf fall season.

Yes some drivers can stop "like the ATO", on dry rails you can even approach open stations slightly faster than the 50kph ATO hits the tailwall at. I believe the ATO brake rate allows for slightly faster approaches than is possible in CM in tunnels however. At Gants Hill IR for example you can stop comfortably in CM if you hit the tailwall at 58-possibly 60kph but you certainly wouldn't want to be doing anymore than that. ATO can do it at 65kph and its certainly not worth trying replicate that!


Another drawback with ATO is if the train underruns at a station where the Starting Signal is red, the Target Speed for the next signaling section is obviously zero and there is a limited time in which you have to switch to Coded Manual and pull up to the signal/fully berth train into the platform before being "code tripped". In this instance, it's safer/more practical to wait for the starter signal to clear or radio the signaller for authority to fully berth the train, preferably in CM but it may be necessary to do this in Restricted Manual if the signaller gives you authority to do so.

Fantastic image!! That said, I wonder whether Joe Public will appreciate someone lovingly caressing the train they are actually on. 

It is certainly possible to in CM.

Regarding rain, What Tom has described is an issue for all ATO systems. The SELTRAC systems can select lower braking rates (and, on SSR, motoring rates) to try and minimise wheel slip or spin. Research continues on having reliable/safety rated speed/position determination that doesn't rely on wheel rotation. Some use Doppler radar, others use accelerometers but this is in addition to the tachometers, not instead of.

There's probably a debate to be had at system level about how much wheelspin/disagreement between tachos is allowed before trains come up in a heap! The ATP system designers tend, reasonably, to be rather conservative.

Up in a heap, the meaning in this that the train has lost code or has been tripped and the emergency brakes are applied, so the train does stop quite abruptly and due to the drawgear may be some buffing between cars, this term is used commonly on the underground.

I’ve been out of the loop on LUL for the past 12 years.Is the Vic Line system an upgraded version of the Central Line system?

No, the Victoria line uses a distance to go radio based system these days.

There was a thread discussing it recently but having done a very brief search I haven't found it....

I thought the key point where Central and Vic ATP differ is that on the Vic "Distance to go" means it's continuously calculated whether the train is following a safe brake profile towards the 'signal' or speed restriction and trip it if not, even before it gets there. Hence the overlap can be shorter and trains can run safely on closer headways. And that's why Vic can achieve 36tph and the Central line system can't be made to do that.