Why cant TBTC stay at a constant speed??

Well, I suppose that TBTC is indeed trying to keep a constant speed.
However, IIRC, the 96 stock, as most (if not all) of the Underground trains, have 3 power notches (shunt, series, parallels i'd say), but I don't think there's a way for the computer behind ATO to choose a specific percentage of the traction power (like, the computer would need to apply exactly a certain percentage to maintain speed). So the ATO system goes up one notch higher when it detects actual speed is below target speed, let the train accelerate, then let it coast when it reaches his target speed, and does it again when speed start to fall more than a few mph below target.

I'm not (at all) a train system expert tho, so I might be wrong. I hope it can help you

Ah, so I was wrong ;D
It seems unbelievable that the software isn't able to determine a needed power percentage and apply it, so that the traction is applied continuously and not in a on/off way. That would be more power efficient too, wouldn't it be ?

Which, interestingly was the very method taught to the original drivers of the first-generation DMUs.......nothing changes then except the method of traction is different .

I only travel on the Jubilee as a passenger and only have my observations rather than any inside knowledge of the system however my perception is that the ATO does not solely use full power when motoring.

There are two reasons I think this,

1. On the longer inter-station sections I use (eg between Canary Wharf and Canada Water), there is a distinct feel and sound of power being reduced but motoring still continuing. I presume this to occur at the point that the target speed has been attained.

2. Between Southwark and Waterloo going west. Sometimes this part of the journey occurs with very slow acceleration and then proceeds at barely more than walking pace but with power applied until the braking point for Waterloo. It definitely isn't full power and feels analogous to the use of the shunt notch on a camshaft controlled train. Not every trip on this section is like this so I presume it depends on the disposition of trains ahead and the decisions of the service regulation software.

I've found the ride at higher speeds on the Jubilee very uncomfortable recently, as it alternately coasts and applies power for a few seconds each. I think quite an improvement could be made just by adjusting the tolerances so the speed will drop by a couple of kph before accelerating up to the limit again.

TBTC is rubbish really it might help run trains run closer together but they are still slow as hell is 30tph now running are they any faster? I wish the jubilee line went for the coded fixed block system where trains go full belt all the time and no stop start power

Actually there is "stop start power" on the Central line, which is fixed block. It just isn't as noticeable.

I almost fell off my chair reading that. Ask any of the Central line drivers here (Auxsetreq, Aslefshrugged, where be ye?) and they'll tell ya the PAC part is hopeless as it comes!

Vic line kit seems to be the best tbh, the driving technique used on TBTC just feels unnatural

Yes the tolerance can be adjusted but for every adjustment that allows the speed to drop an extra kph the line is losing capacity. As the Jubilee is now constrained by the number of trains available every second counts for the trains to keep as close as possible to max speed. Unfortunately this does result in the on/off nature of the train traction at times.

Coasting isn't part of the Seltrac system out of the box and the PPP did not sufficiently incentivise it being added (in fact it PPP pretty much did the opposite - make the most out of the least cost).

The fact that any one failure (for example a closed track) requires intervention from the signal operator, and if that intervention does not happen (e.g. failure of radio) the train will sit there all day.

Under conventional signalling, providing in an automatic area the train can apply the rule after 2 minutes.

Under TBTC the whole line is effectively "semi-automatic", so any failure requires the train's progress to be carefully watched through the failing section.

Feedback from controllers indicates the workload is simply too difficult to manage during times of disruption.

This is correct.

67's would trip out at 57 mph. They could reach that speed occasionally between Highbury and Kings X southbound. A little additional tap on the brakes would just reduce it though.



Not to mention couplers and motors to suffer too!

I don't know much about TBTC to be honest, except to say that it's default mode appears to be "walk em out again"

The Central's signalling has been greatly modified over the years, it's reliable and it's an elegant set-up in so much as when the ATO fails the train can be driven manually, and more comfortably to full line speed, and human beings seem to deal with poor adhesion problems far better than the machinery. 'Defensive Driving' it's called............

The ATO is another story all together. Unreliable and fickle the only thing it's ever done in my opinion is to wreck the trains. And remember, the trains were purposely built for it. It's full on, full off whether for an inch or a mile. The punters get thrown about all over the place, and the doors play up as the acceleration/braking causes door proving problems which results in lost time as the drivers plead for the punters not to lean against the doors otherwise we're gonna be stuck here all day. It gets so bad at times that one has to give up with the ATO and drive it manually because a train hammering into an over crowded platform is downright risky and a slower acceleration deals with the door proving problem.

I can't speak for other lines, but it's a myth to say that ATO is better and faster. Even with a traction fault a train can be manually driven without losing any time at all. In fact if a driver knows how to tweak the codes he can ever so slightly out run ATO

If I had my way I'd dump the lot and bring back the guards. They were great............