5mph through stations

[trc666]

Why is it trains have to slow down to 5mph (or stop completely in the case of the Victoria line ATO) through tunnel stations when non-stopping, but can travel at linespeed when passing through surface stations?

[Deleted]

trc666 said:

Why is it trains have to slow down to 5mph (or stop completely in the case of the Victoria line ATO) through tunnel stations when non-stopping, but can travel at linespeed when passing through surface stations?

As the overlaps are bigger on the likes of the met. Most other places have short overlaps at stations.

[Colin]

Not all surface stations can be passed above 5mph - most can only be passed at restricted speed (on the District, where authorised, we can do 25 mph) - certainly not full line speed. I suspect the Met & Picc are obvoius exceptions to the rule - but absolutely not every station on every line!!

As Met Service Op says, it's all to do with the designed overlap of the station starting signal - ie, trains leave platforms at a slower speed, so the signalling is set up to reflect this.

[Deleted]

colin said:

Not all surface stations can be passed above 5mph - most can only be passed at restricted speed (on the District, where authorised, we can do 25 mph) - certainly not full line speed. I suspect the Met & Picc are obvoius exceptions to the rule - but absolutely not every station on every line!!

Certainly on the met, every station north of Harrow on the Hill on the met main (including the watford branch) can be past through at line speed.

You can do it on some places on the picc too, but only a handful of stations.

[Deleted]

Where the District runs on Network Rail (East Putney to Wimbledon, Gunnersbury to Richmond) there's no restriction when non-stopping stations either.

[trc666]

Would this apply to the Bakerloo north of Queen's Park?

[Deleted]

Yes, it would.

Personally I think that having full (or 3/4) overlaps at station starters is best - with the new DTG ATO coming on line for the SSL, this type of installation may be a possibility.

[Deleted]

just to add temple e/b has a full speed overlap on the station starter

[Deleted]

theonekea said:

Yes, it would.

Personally I think that having full (or 3/4) overlaps at station starters is best - with the new DTG ATO coming on line for the SSL, this type of installation may be a possibility.

The Central has DTG ATO and slows down whilst any part of the train is within the platform limits. However, it's a bit more than 5mph.

[Deleted]

That's because it's a fixed block system that uses track circuits; AFAIK the track circuits beyond the starters are simply laid out in the same way as other 5mph installations.

[Deleted]

theonekea said:

Personally I think that having full (or 3/4) overlaps at station starters is best - with the new DTG ATO coming on line for the SSL, this type of installation may be a possibility.

The reason you havnt got full speed overlaps at most stations is because there simply isnt the need to have something there that is rarely used to its full potential. On most occasions, trains are not doing much more than 5 mph past the starter because they have just opened up from a stand.

With ATO, yes this could be different, but i still dont see why, because as i say, in most locations a full speed overlap isnt needed at a station.

[edb]

Just to Add my two cents, why when travelling between Holborn and TCR on the Central line does the train slow so much when passing the old british museum station. I appreciate there is a crossover in that area but it seems to slow to an almost stop and as has been discussed elsewhere on this board crossovers can be passed rather faster that a stop.

[Tubeboy]

Havent been through that stretch in a while. Guessing, errr, track geometry, condition of track, or approached control signal. Also tsr/psr?

[edb]

I did wonder if it may be due to old signalling systems, we slow down right at the platform. but i have disregarded this idea as i though all the signalling was updated as the line went ato

[greatplum]

I go through regent's Park every day and it is interesting that each driver seems to have a different idea of what to do. SOme drivers stop completely, some drive through the station at about 5 mph all the way through and a few touch 5mph briefly before accelarating off - what should they be doing?

[Phil]

greatplum said:

I go through regent's Park every day and it is interesting that each driver seems to have a different idea of what to do. SOme drivers stop completely, some drive through the station at about 5 mph all the way through and a few touch 5mph briefly before accelarating off - what should they be doing?

The 'feeling' will differ according to where you are sat in the train!

AIUI the idea is to slow normally as station as entered, move past starter at 5mph: as soon as cab has passed, accelerate back to line speed.

[c5]

greatplum said:

I go through regent's Park every day and it is interesting that each driver seems to have a different idea of what to do. SOme drivers stop completely, some drive through the station at about 5 mph all the way through and a few touch 5mph briefly before accelarating off - what should they be doing?

It may also depend on what aspect the station starter is showing...
Though off course most operators have a different driving technique.

Some operators may still be in the platform stopping way of thinking and then motor on.

[Deleted]

When Mornington Crescent was closed for the long period of modernisation, etc. I was on a N/b 59ts to High Barnet, think then the starter signal must have been permanently off or the sections ahead were completely empty. Anyway, left Euston, must have shut off as entered the platform, then wound up fully... must have gone through at 25mph.... weird feeling that was.

[Deleted]

Is the fact that the rails in tube tunnel stations are not sitting on full sleepers and ar set in concretete a factor?

At open staions it is always surprising to watch how much the sleepers move as the wheel is directly above.

Perhaps someone in the know could comment!

[Tom]

They have. Posts 2 &3 in this thread.

[Deleted]

tom said:

They have. Posts 2 &3 in this thread.

Oh no they have'nt.

Neither mentions sleepers, but rather overlaps, with post 3 elaborating: "overlap of the station starting signal".

Surely neither of these is referring to incomplete sleepers!?

[Colin]

I think Tom was trying to say that sleepers have no connection at all to the set up of signals.

Whilst the condition / type of sleepers may play a part in deciding the line speed for a particular area, I don't think it makes a huge difference. Ballast in open sections is used for drainage (ie, rain) - not something that's such an issue in tunnels.

[tubeprune]

The "5 mph at Starters" rule is:

"....the speed of the train must be reduced to 5mph/8kph at the station starting signal, from which point the train can be accelerated in the normal manner." (Tc112)

It has nothing to do with trackwork or sleepers. The reason is the existence of what is now called "compromised overlaps". Station starters were originally designed to have very short overlaps. This allowed the home signal in rear to clear quickly behind a departing train and thus let the next train in sooner. The short overlap was permitted because most trains would be stopping and the risk of a full speed SPAD was minimal.

Some drivers took a very liberal view of 5 mph and, as far back as the 1970s, it was decided that the (very small, IMHO) risk of a full speed SPAD at a starter was unacceptable and that all overlaps should be full speed. To mitigate the risk before resignalling of each location took place, many starters were converted to approach control to force drivers to slow down.

I believe this is still the situation today.

[greatplum]

rbruce1314 said:

greatplum said:

I go through regent's Park every day and it is interesting that each driver seems to have a different idea of what to do. SOme drivers stop completely, some drive through the station at about 5 mph all the way through and a few touch 5mph briefly before accelarating off - what should they be doing?

The 'feeling' will differ according to where you are sat in the train!

AIUI the idea is to slow normally as station as entered, move past starter at 5mph: as soon as cab has passed, accelerate back to line speed.

I always sit in the same part of the train - I'm sad like that! Creature of habit!

[Tom]

tubeprune said:

Some drivers took a very liberal view of 5 mph and, as far back as the 1970s, it was decided that the (very small, IMHO) risk of a full speed SPAD at a starter was unacceptable and that all overlaps should be full speed. To mitigate the risk before resignalling of each location took place, many starters were converted to approach control to force drivers to slow down.

I believe this is still the situation today.

Sort of. When signalling the layout you should provide a full speed overlap on the starter unless there are headway constraints assosciated with it, in which case a 35kph overlap is acceptable.

The approach control on the starter is to prevent compromised overlaps but not on the starter itself. (If you SPAD the starter at line speed the effect will be the same; regardless of if it is remaining at danger for a train ahead or because the platform timing section has not yet run it's time). The signal with an overlap that is potentially compromised is the next signal on the inter-station run. This is because the train performance curve the overlaps are calculated from are based on the train starting from the previous station at rest. If the train passed the previous station at line speed, it has the potential to attain a higher speed than if started from rest and hence the overlap may be inadequate.

The idea is that the approach control will enforce the observation of the 5mph rule and hence any reacceleration is similar to the train starting from rest.

EDIT: Sorry for bumping a pretty dead thread - but the link from Colin in another thread pointed me to it and I felt the subject needed some claification.

[Deleted]

Well "bumped" Tom, as I hadn't noticed this thread previously !

As you say, a number of locations are approach controlled and the starter will not clear until it's pre-conditions (time and or speed) have been satisfied. However, there is no obvious risk if the subsequent signals are green and thus the route is clear (unless a speed restriction is also being governed).

Cannon Street being an obvious example that fails to recognise this, it is quiet possible to be down to 5mph by the starter, but it will not clear if the train speed was not down to 15mph by the timing point half way along the platform ... in which case the train must now stop and time out before the signal clears ....but this is all pointless, when the station is closed and the advance starters (both on the eastbound and westbound ) can be seen showing green. The train has thus been delayed unnecessarily. (subject to my penultimate paragraph)

As a further thought ... which may be what Tom is saying in a very Techy way .... presumably it's not the starter's overlap that is in issue, but the inner home signal. It is the Inner home that clears you up to the starter when there is not a full speed clearance from the next signal (ie. the starter). In laymans terms, the last signal before the station will let you into the station when the back of the train in front has only just passed the signal. The starter it's self will not clear until the train in front is a full speed spad distance beyond the next signal (advance starter) which is generally a long way off.

I rather think this system is a touch dubious since it relys on a driver not loosing concentration upon entry to a platform at the same time as another train has been stopped just beyond the same platform ! anyway ...........!!!!

Of course if the starter is green then there is no real risk whatever speed the train is doing, unless the next, advance starting signal, relys on that train only having been able to attain a defined speed before reaching it ...given the distance most of them are from the starter I'd say there aren't too many of them. The risk from my preceding paragraph pertaining to the inner home is surely much greater.

sorry to go on !!! ;D ;D ;D

[Deleted]

just to claify something aspect cannon street westbound has 2 timing sections one 4 1/2 sec and one 15 sec the 15 sec is the last track circuit before the starter and is only about 15-20 feet long

[Tom]

aspect said:

Well "bumped" Tom, as I hadn't noticed this thread previously !

Of course if the starter is green then there is no real risk whatever speed the train is doing, unless the next, advance starting signal, relys on that train only having been able to attain a defined speed before reaching it .

That's what I'm saying, though the signal may just be an intermediate running signal.

On the Underground we calculate all our overlaps (as opposed to the NR method of making it a set 180m beyond the signal).
Included in the overlap calculation somewhere (actually in a few places) is a value for the speed of the train when it trips which we call v (foir velocity, I guess).

Therefore we need to know what value v should be to use it in the equation, and the way we do that is by working out, based on train performance data, what speed the train will be doing at that point assuming it starts from rest at the previous station.