S Stock Speed Musing...

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....

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....

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.

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.

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.

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.

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!!}

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.

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.

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.

'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!!