S Stock Speed Musing...

[mrjrt]

I seem to recall reading recently that the S Stock will be limited to 60mph.

Would it not have been better to have specified stock that can run in the more conventional suburban 75-90mph range, enabling Chiltern's stock to also run faster, reducing journey times and increasing capacity on the fast lines down to Harrow on the Hill?

I know there's usually a trade-off between top speed and acceleration, but the Met trains will spend a lot more of their time between Baker Street and Amersham than Baker Street and Aldgate (yes, I know you have to factor in the Circle and District as they'll be sharing the stock, but I don't think it'd make that much difference to the design.)

I guess an alternative would be to hand over Rickmansworth to Amersham to Chiltern and transfer over the fast lines to NR (freeing them to do whatever they like), effectively segregating the services (though they'd probably need to finish the widening project from all those years ago, widening from Watford South Junction to Rickmansworth). I seem to recall this being dismissed before as Marylebone wouldn't be able to handle the traffic.

...or resume the Met serving Amersham to Aylesbury and let Chiltern serve Aylesbury en-route to Bletchley from Princes Risborough. though as I say above, you'd probably want the 75-90mph speeds for that.

Anyway...just musing.

[Colin]

There's far more to it than that!!

The obvious starter for ten is the condition of the track. The track has to be capable of those speeds, and they'd have to be constantly maintained to a high level too. That alone can be killed on cost versus benefit grounds.

Then there's the signalling. I don't know what the current signalling allows for but I bet it's limits are probably 60mph. To increase the line speed you would undoubtedly have to improve the signalling to match - I'm talking recalculating overlaps, re-sighting signals so they can be seen properly, etc. Again, cost would rule it out; and even more so than the track as signalling is big bucks.

Traction current is being upgraded to a higher voltage, so it may be able to work with higher speeds, but I wonder if the upper limit with 4 rails is the same as with 3 rails If it isn't the idea is dead in the water before it's even started.

The last factor is this: is anything more than 60mph really necessary? Even on just the Met alone you are trying to cater for a very small part of the line as a whole. Factor in the whole SSR and the area is minuscule to the point it's really not justified.

This thread may be better suited to the Railway Ideas Proposals and Suggestions area but we'll see how it goes....

[Ben]

The tracks being upgraded because of 'S' stock though isn't it? Its only the advent of the A stock being limited to less than 70mph that has regrettably allowed the current track to be maintained to a less than optimal standard. Bit short sighted really as if the infrastructure isn't used optimally then it doesnt provide as high a return on capital invested in it.

The signalling will be replaced in the long term, but can a derrogation order not be issued for the current signalling as it met standards when installed and I wouldn't have thought has changed significantly? Aside from Watford South Junction that is.

When you say upper limit Colin, do you mean traction current, voltage, or speed obtainable? Max speed obtained on third rail is 108mph by a 5Wes (cl. 442). The former eurostar areas are using 850V DC aswell, not a clue on max current drawn however!

The class 165/0s max speed is 75mph. Whilst the area theoretically capable of such a speed is limited, I wouldnt go as far as saying its miniscule. Finchley Rd - Amersham, half of that 4 track aswell. Say about half of the total length is capable of 75mph, to keep up with Chiltern, it would still produce a noticable change to timings for passengers compared to, what, 50mph atm?

Necessity is a false prophet here; so much has been done on the system that isn't necessary atall, but surely anything that improves capacity or the traveling publics experience of the tube is at least closer to approaching a sense of necessity than new roundles, poor quality paint/tiling/signage...

Finance aside (we all know nobody has two brass farthings to rub together anymore and wont do for some time), it stil requires political will, both internally and externally.

You never know, could be that the S stock manages a few mph better than its design brief?

[Colin]

Sept 12, 2010 3:42:31 GMT Ben said:

The tracks being upgraded because of 'S' stock though isn't it?

It's being upgraded in terms of continuously welded flat bottom rail on concrete sleepers which gives a far smoother ride than bullhead rail with fish plate joints all over the shop - whether that's giving a potential increase in line speed too I don't know but I was once told it was being done "cos if it ain't done, the new trains will bounce off the tracks". I'm no Pway engineer so I can only go on what Pway persons tell me....

Sept 12, 2010 3:42:31 GMT Ben said:

The signalling will be replaced in the long term, but can a derrogation order not be issued for the current signalling as it met standards when installed and I wouldn't have thought has changed significantly? Aside from Watford South Junction that is.

Whilst the signalling may have once upon a time been designed such that trains could operate at higher speeds, it would have been designed according to the characteristics of the stocks running at the time. S stock isn't A stock and will have different acceleration and braking profiles. The same can be said for Chilterns - they ain't A or S stocks and will have a differing profile too.

A good example of this is the "compromised overlap project", particularly on the District line. Some bright spark worked out that the D stocks had an inferior braking profile compared to the previous R stocks and as a result some signals, when SPADed (passed at danger without authority), could lead to the risk of a collision with a train if it were stationary ahead. So my point is just because a particular stock, or the signalling system itself, may have historically allowed something it doesn't necessarily automatically mean the same is true if you change the rolling stock.

Sept 12, 2010 3:42:31 GMT Ben said:

When you say upper limit Colin, do you mean traction current, voltage, or speed obtainable? Max speed obtained on third rail is 108mph by a 5Wes (cl. 442). The former eurostar areas are using 850V DC aswell, not a clue on max current drawn however!

Speed obtainable in terms of there must come a point when the pick up shoes are not making good contact with the traction current rails and thus not getting enough 'juice' to keep the motors going. So I'm thinking physically there must be a practical limit. If 4 rail can achieve the same as 3 rail with no adverse problems, well then fair enough.

Mind you, the motors themselves will of course have a limit as to what they can achieve, and that will in turn depend on what it's supplied with I suppose, though 3rd rail does indeed prove that 750v DC is quite enough to get something humping along.

Sept 12, 2010 3:42:31 GMT Ben said:

The class 165/0s max speed is 75mph. Whilst the area theoretically capable of such a speed is limited, I wouldnt go as far as saying its miniscule. Finchley Rd - Amersham, half of that 4 track aswell. Say about half of the total length is capable of 75mph, to keep up with Chiltern, it would still produce a noticable change to timings for passengers compared to, what, 50mph atm?

The 4 track section isn't even from Finchley Road - it's more like Neasden, and it ends at the Watford curve. Although it is about 21km, we are referring to the fast tracks only not all 4 tracks; trains stopping all stations on the local tracks wouldn't be doing +60mph between stations and Chiltern don't use the local tracks either. In fact bringing it all into perspective, Chiltern only uses the Met fast between Harrow and Watford curve - just 9km.

So given the size of the Met as a whole, and the tracks we're talking about, there is a big difference in sizes of areas. And that's without the whole of SSR, like I said.

Sept 12, 2010 3:42:31 GMT Ben said:

surely anything that improves capacity or the traveling publics experience of the tube is at least closer to approaching a sense of necessity than new roundles, poor quality paint/tiling/signage...

Yes, but the point I'm trying to get across is that you can't just build a train that goes faster then plonk it on the railway and say that capacity is increased. It's the signalling that dictates capacity so you can build faster trains all day long but they won't make any difference without the signalling being changed to match.

Sept 12, 2010 3:42:31 GMT Ben said:

You never know, could be that the S stock manages a few mph better than its design brief?

Quite likely, but in the end line speed is line speed.

_{distances in this thread are taken from the Met WTT - hopefully I've got them right!!}

[Deleted]

I've never really understood why the new S Stock is governed to 100 kph (62 mph). I am told they are very similar in design to the class 378s which have a design speed of 75 mph and will rarely reach the highest line speed of 60 mph due to being on stopping services. The S Stock however in theory will spend a lot of its time at maximum speed on the express sections.

In fact thinking about top speeds I believe the Jubiliee line trains 1996 stock are now the fastest. I've travelled on the Central lines 1992 stock and they seem to be governed to 85 kph (53 mph) down from their design speed of 100 kph (62 mph)

I believe on the NR lines from Neasden Junction up to Harrow on the Hill the line speed goes up to 75 which the turbos reach really quickly. I also believe beyond that (but i could be wrong) that NR trains are permitted higher speeds than the 50 mph the A stock is limited to beyond Harrow on the Hill towards Amersham. I don't know what those speeds are as they aren't in the sectional appendix

In terms of acceleration does has anyone timed how quick an S stock is? The class 378 seems to take around 30 seconds to reach 45 mph from a standstill.

In comparison with Paris - the top speed of the Metro is 70 kph (43 mph) with the exception of driverless line 14 where 80 kph (50 mph) is permitted. However the stations on average are much closer together than ours. A better comparison would be the RER lines when they cross the city (think crossrail) and they are permitted to do 100 kph (62 mph) using in cab signalling. (Line A). However outside of the centre as they each well beyond the Parisian suburbs to places such as Etampes and Dourdan (Line C) , line speed permitting those trains have design speed of 140 kph (87 mph)

[Deleted]

I was told the 1995/96 stock ungoverned will also do 75 mph, then again once you get above a certain speed (40/45?) on them there is quite a horrifying rumbling/vibrating noise but it's only very noticeable on the 96 stock.

I think 60 mph is sensible because alot of the track up there is the ancient old bullhead variety and it would surely be quite dangerous going to fast.

[metrailway]

Sept 12, 2010 12:15:50 GMT @notatraindriver said:

I believe on the NR lines from Neasden Junction up to Harrow on the Hill the line speed goes up to 75 which the turbos reach really quickly. I also believe beyond that (but i could be wrong) that NR trains are permitted higher speeds than the 50 mph the A stock is limited to beyond Harrow on the Hill towards Amersham. I don't know what those speeds are as they aren't in the sectional appendix

You are right that the Turbos are faster than the A Stock on LUL infrastructure. They're allowed to go up to 60mph between Harrow and Amersham.

Speeds for the Turbos on the Aylesbury line are:
Marylebone - Willesden Green - 50mph
Willesden Green - Neasden Junction - 60mph
Neasden - Harrow South - 75mph (then 60mph from Northwick Park for NB trains)
Through Harrow - 40mph
Harrow North - Watford South - 60mph
Through Ricky - 25mph
Ricky - Amersham - 60mph
Amersham - Aylesbury - 75mph

I believe that they were able to go full pelt (75mph) before 2003 (I think). I remember the time to reach Rickmansworth from Harrow would take only 7 mins

[Oracle]

When was A Stock reduced down from 70 mph? As I keep reminding ad nauseum, the D78 Stock on the Metroliner Tour was given the 'pedal to the mettle' northbound on the run to Amersham with the intention of reaching the then-linespeed of 70.

[Deleted]

I'm not sure how quick the D78s are but watching the series called "The Tube" the lady driver seemed to have the Combined Brake Power Controller in the full motoring position for long periods of time.

Thanks for the info on the line speeds for the Turbostars. I've been told by Chiltern drivers that whilst they can go a little faster the A stock can brake a lot better!

[Deleted]

Talking of which its a shame that on the shared tracks between Queens Park and Harrow & Wealdstone/Watford Junction that Overground trains aren't allowed faster speeds than LU trains. In fact I'm not even sure how capable the 1972 stock are of reaching the 45 mph line speed between stops. I will have to check with my gps.

[mrfs42]

Sept 12, 2010 17:39:47 GMT @delboy200 said:

I think 60 mph is sensible because alot of the track up there is the ancient old bullhead variety and it would surely be quite dangerous going to fast.

ITYF that Mallard set the record on a ropey bit of bullhead!

[Deleted]

Sept 12, 2010 20:30:09 GMT @notatraindriver said:

Talking of which its a shame that on the shared tracks between Queens Park and Harrow & Wealdstone/Watford Junction that Overground trains aren't allowed faster speeds than LU trains. In fact I'm not even sure how capable the 1972 stock are of reaching the 45 mph line speed between stops. I will have to check with my gps.

Whilst the line speed prior to the 1988 resignalling was 60 mph, the 45 mph south of Harrow & Wealdstone was the result of a trial with a 313 tripping at 60 mph and running a considerable distance before it stopped. The HMRI were concerned at BR stock running into LT stock as had occured on two previous occasions.

[Deleted]

Maybe then with the 313s gone the line speeds can be increased? I think the brakes on a 378 are better than a 313. Also the 45 mph line limit goes all the way to Watford Junction. So are NR trains more prone to passing signals at danger than tube drivers on the same stretch of line?

[Colin]

'Main line" stock, as opposed to LU stock (probably the easiest way to talk about the two) have poorer braking.

This is what I was getting at in reply #3 above when I spoke of braking profiles. LU stock routinely stops in shorter distances simply because they have far superior braking. You have to take into account all the characteristics of a given rail stock, not just it's top speed!!

[citysig]

Sept 12, 2010 3:42:31 GMT Ben said:

The tracks being upgraded because of 'S' stock though isn't it? Its only the advent of the A stock being limited to less than 70mph that has regrettably allowed the current track to be maintained to a less than optimal standard. Bit short sighted really as if the infrastructure isn't used optimally then it doesnt provide as high a return on capital invested in it.

Just to pick up on this point a few posts back.

The track is being slowly upgraded, but not just with the S-stock in mind - work is needed in certain areas anyway.

The A-stock being limited and the condition of the track are 2 separate issues and are not related.

The A-stock were limited due to age (and to try and preserve them as long as possible).

The track is not maintained in relation to A-stock top speed - the track is maintained as far as money allows. Areas of "rough" track will have speed restrictions for all stock until they are replaced.