Why is Thameslink central section linespeed so slow?

[tasky]

According to Open Rail Map the maximum line on Thameslink between Elephant and Castle and St Pancras is 30mph - it certainly feels very slow when you're on the train.

Is there a particular reason for this? Obviously there are a lot of stopping services in a densely built up area, but 30mph seems to be unusually slow, especially for such a straight rail way. I don't think many other heavy rail lines are limited to 30mph except on curves and around station throats, for obvious reasons.

For example the North London Line for instance is mostly 40-45mph except on curves, the West London Line 60mph.

Is there an interesting reason behind Thameslink being particular slow? Given it's been upgraded recently it is quite surprising to me.

 

[59CosG95]

According to Open Rail Map the maximum line on Thameslink between Elephant and Castle and St Pancras is 30mph - it certainly feels very slow when you're on the train.

Is there a particular reason for this? Obviously there are a lot of stopping services in a densely built up area, but 30mph seems to be unusually slow, especially for such a straight rail way. I don't think many other heavy rail lines are limited to 30mph except on curves and around station throats, for obvious reasons.

For example the North London Line for instance is mostly 40-45mph except on curves, the West London Line 60mph.

Is there an interesting reason behind Thameslink being particular slow? Given it's been upgraded recently it is quite surprising to me.

The age and condition of the viaducts might have something to do with the E&C - Blackfriars section. And underground, Blackfriars - St. Pancras is full of sinewy twists and turns.

 

[AM9]

According to Open Rail Map the maximum line on Thameslink between Elephant and Castle and St Pancras is 30mph - it certainly feels very slow when you're on the train.

Is there a particular reason for this? Obviously there are a lot of stopping services in a densely built up area, but 30mph seems to be unusually slow, especially for such a straight rail way. I don't think many other heavy rail lines are limited to 30mph except on curves and around station throats, for obvious reasons.

For example the North London Line for instance is mostly 40-45mph except on curves, the West London Line 60mph.

Is there an interesting reason behind Thameslink being particular slow? Given it's been upgraded recently it is quite surprising to me.

Given the short distances between Blackfriars, City Thameslink and Farringdon, and the fact that all trains stop at all stations, there isn't much opportunity to go much faster. They could go a bit faster between Farringdon and the curve at the end of the old Kings Cross Thameslink station, especially with the consistency of ATO, but with 2.5m headways planned, it's better to keep to a speed where trains don't queue outside every station whilst the previous one clears.

 

[notverydeep]

It will be interesting to see if Automatic Train Operation (ATO) permitted speeds will higher for parts of this corridor. On other railways, ATO allows the speed profile to be varied as the maximum speed permitted by the track geometry and condition allows, even where this is only for a relatively short distance. This in turn allows worthwhile run time savings, particularly when applied to high demand, high frequency routes. This is further helped by the availability of more speed steps than just those rounded to the nearest 5 mph, as they would tend to be for drivers.

Taking St. Pancras International to Farringdon as an illustration, even an increase to 35 mph after the curves at the St. Pancras end to shortly before the curves approaching Farringdon would be a worthwhile gain. If this stretch is a mile of this 1.36 mile link, the saving would be around 18 seconds per train.

An illustration of this ability to allow more speed variations in current operation is the eastbound Central line (a 30 + trains per hour railway) into Liverpool Street, where trains noticeably accelerate after a speed restriction, even as they enter the platform, before slowing to a stop further on. Both Human factors and defensive driving standards would tend to encourage a driver to keep a constant speed in this case with normal manual driving as the speed limit lifts only a little way before further braking is required.

 

[Bald Rick]

Someone asked this very question only a few weeks ago, but I don’t have time to dig out my answer to it back then.

In short, the linespeed has actually been raised in sections through the Thameslink programme, and here will be a fraction more with ATO. But in principle it is a very twisty railway both horizontally and vertically.

 

[Bald Rick]

If this stretch is a mile of this 1.36 mile link, the saving would be around 18 seconds per train

It isn’t, and it wouldn’t.

From the end of the curve at the south end of KX Thameslink to the start of the curve (horizontal and vertical) at the intersection bridge north of Farringdon is about 500 metres. And it isn’t even straight through that section. The trains are 240m long, and need time to accelerate and brake too.

 

[tasky]

Thanks for the interesting answers

 

[swt_passenger]

Thanks for the interesting answers

Here’s the recent thread Bald Rick mentioned, may give more info:
https://www.railforums.co.uk/threads/why-is-the-thameslink-core-so-slow.177357/

 

[tasky]

Here’s the recent thread Bald Rick mentioned, may give more info:
https://www.railforums.co.uk/threads/why-is-the-thameslink-core-so-slow.177357/

Apologies for not doing a better forum search! And thanks

 

[Bald Rick]

Here’s the recent thread Bald Rick mentioned, may give more info:
https://www.railforums.co.uk/threads/why-is-the-thameslink-core-so-slow.177357/

Thanks for digging this out.

 

[ComUtoR]

According to Open Rail Map the maximum line on Thameslink between Elephant and Castle and St Pancras is 30mph - it certainly feels very slow when you're on the train.

50mph through Elephant. 40mph towards Southwark Bridge Junction then it drops to 30mph

 

[notverydeep]

It isn’t, and it wouldn’t.

From the end of the curve at the south end of KX Thameslink to the start of the curve (horizontal and vertical) at the intersection bridge north of Farringdon is about 500 metres. And it isn’t even straight through that section. The trains are 240m long, and need time to accelerate and brake too.

I accept that longer trains do make a difference, as a part of the train will occupy the constrained section for longer than a shorter train at any given speed. However, the Thameslink core isn't the only rail link between somewhere near St. Pancras to somewhere near Farringdon that should start ATO running this year and on the other one there will be short distances of higher speed running plus better acceleration permitted and these will generate an improvement in run time of 31 seconds in one direction and 33 seconds in the other, despite having broadly similar curvature (apart from the curves between the old and new Thameslink platforms).

Elsewhere on the other network, potential higher ATO speeds over 500 metres or even less are generally being taken up. These add up to savings not just for passengers, but shorten the round trip time and the number of trains that had to be bought for the desired peak frequency. It would be a surprise if no survey and appraisal of speeds that can be permitted in ATO on Thameslink hasn't been undertaken. High frequency benefits from consistent operation of each successive train, but that isn't the same as requiring a constant speed across each link to achieve consistent reoccupation times headways. Shorter run times considerably enhance the economic case for resignalling beyond the mere frequency uplift.

 

[cle]

Someone asked this recently, and there was a bit of a pile-on. There are reasons, but it does feel slow, that is undebatable.

I think it feels slower than the tube, as the units are built for more - so it feels constrained. Like revving on the brakes. I think it could be a bit nippier, and of course dwell times/padding is absurd too - hopefully ATO and higher tph will force this. It should be able to act a as a tube alternative, which needs relief (and this has capacity, even in peaks) - but it needs to be quicker.

 

[Bald Rick]

I accept that longer trains do make a difference, as a part of the train will occupy the constrained section for longer than a shorter train at any given speed. However, the Thameslink core isn't the only rail link between somewhere near St. Pancras to somewhere near Farringdon that should start ATO running this year and on the other one there will be short distances of higher speed running plus better acceleration permitted and these will generate an improvement in run time of 31 seconds in one direction and 33 seconds in the other, despite having broadly similar curvature (apart from the curves between the old and new Thameslink platforms).

Elsewhere on the other network, potential higher ATO speeds over 500 metres or even less are generally being taken up. These add up to savings not just for passengers, but shorten the round trip time and the number of trains that had to be bought for the desired peak frequency. It would be a surprise if no survey and appraisal of speeds that can be permitted in ATO on Thameslink hasn't been undertaken. High frequency benefits from consistent operation of each successive train, but that isn't the same as requiring a constant speed across each link to achieve consistent reoccupation times headways. Shorter run times considerably enhance the economic case for resignalling beyond the mere frequency uplift.

The Met line station at KX is 1/2 a click closer to Farringdon than the TL station at St P, and also doesn’t have to negotiate either the curve through the former KX Thameslink, nor do the winding around and under the original Met at the West end of Farringdon. And half of the trains on the Met are less than half the length of a 12x700. On the (relatively) straight section on the Widened lines of around 500metres there simply isn’t the space for a 700 to accelerate to anything more than about 35mph once clear of KX TL before having to brake again for the Farringdon curves. The saving would be about 3 seconds. Negligible, and moser importantly, not practical to take the saving into the timetable. It would just be lost in dwell time. As an aside, ATO will not improve the acceleration of the 700s - the drivers already know how to do that.

I can see how it will help on the Met, though. Longer straight sections, shorter trains, etc.

Someone asked this recently, and there was a bit of a pile-on. There are reasons, but it does feel slow, that is undebatable.

I think it feels slower than the tube, as the units are built for more - so it feels constrained. Like revving on the brakes. I think it could be a bit nippier, and of course dwell times/padding is absurd too - hopefully ATO and higher tph will force this. It should be able to act a as a tube alternative, which needs relief (and this has capacity, even in peaks) - but it needs to be quicker.

There is no recovery time (‘padding’) in the TL core between Blackfriars and St Pancras and vice versa. The current timetable is the ATO timetable, with services dropped out. Which is why it is 3 minutes quicker on this section in the peak than it was a year ago. It is testament to the professionalism of the driver that most can keep to the time she without delay.

And, it does act as a tube alternative. Witness TL trains leaving London Bridge northbound in any morning peak, and in particular how many people board them there. This service did not exist a year ago, and indeed never really existed in peak times (aside from 1 train in each peak).

 

[Ethano92]

There is no recovery time (‘padding’) in the TL core between Blackfriars and St Panc

Just a few weeks ago my driver had enough time at Farringdon to let the train sit in the platform for a minute or 2 whilst he went to the toilet. Didn't even need to run back to his cab, he leisurely walked back. Although I do doubt this is purposely timetabled padding, from experiences I've had with the core off peak when things are running on time, trains will almost always sit in the platform from St Pancras to City thameslink (in regards to the core section) for anything from 30 seconds to 2 minutes after boarding is complete. Not just at one of the 3 either, all 3 of them consecutively. To me this is the bit that feels slow rather than the actual speed since stops are so close together although I will admit it feels as though not all drivers make use of the 700s impressive acceleration even when a few minutes late

 

[Bald Rick]

Just a few weeks ago my driver had enough time at Farringdon to let the train sit in the platform for a minute or 2 whilst he went to the toilet. Didn't even need to run back to his cab, he leisurely walked back. Although I do doubt this is purposely timetabled padding, from experiences I've had with the core off peak when things are running on time, trains will almost always sit in the platform from St Pancras to City thameslink (in regards to the core section) for anything from 30 seconds to 2 minutes after boarding is complete. Not just at one of the 3 either, all 3 of them consecutively. To me this is the bit that feels slow rather than the actual speed since stops are so close together although I will admit it feels as though not all drivers make use of the 700s impressive acceleration even when a few minutes late

It happens on entering the core because the timetable isn’t full. If a train arriving at St P has a 5 minute gap rather than a 2.5 minute gap in front of it, and is on time at Kentish Town, it will use the recovery time that would usually be spent standing in the tunnel in the platform instead.

I agree that the running times between the core stations are a little generous, but this is simply because they are the same as the 319s, and the 700s are a much better train. When the 24 tph timetable is in, and running well, then Ismail unspectacular the timings will be tightened a little.

 

[DerekC]

When the core section of Thameslink was being assessed for higher capacity there was a push to get the line speed increased from 30mph to 40 mph - not so much because of a reduction in sectional running times but because it would have helped reduce platform reoccupation time. But it ended up on the "too difficult" pile - largely (I think) because there was no real science behind the line speed in the first place, so nobody could show whether an increase would be safe or not. I think in retrospect it should have been pushed harder.

 

[big all]

slower speed equals smaller headways as in when you drive a train over borough market at london bridge you would be perhaps 10 coach lengths behind a kent coaster doing 15-20mph with 1.5 signals in between
in other words more like walking behind someone where your reactions would stop you dead if they stopped
then if you throw in a bit more line speed you have far more flexibility to close up on the train in front
in other word working to reduced speeds gives you far more operational flexabillity and opertunities to bunch up to make up time or hang back as your early or on time

 

[Bald Rick]

When the core section of Thameslink was being assessed for higher capacity there was a push to get the line speed increased from 30mph to 40 mph - not so much because of a reduction in sectional running times but because it would have helped reduce platform reoccupation time. But it ended up on the "too difficult" pile - largely (I think) because there was no real science behind the line speed in the first place, so nobody could show whether an increase would be safe or not. I think in retrospect it should have been pushed harder.

I’m not sure the push was very hard, it was more of an idea. And as stated above, very quickly realised it would only be of benefit for a short section betweeen KX TL and Farringdon, with minimal actual journey time reduction, and it would also have had an effect on capacity.

 

[edwin_m]

There's a tradeoff between speed and headway - at low speed the train takes longer to enter and leave platforms and pass other places. The exact answer depends on train length and acceleration but I think the optimum speed for maximum capacity is somewhere around 40-50mph.

 

[Bald Rick]

There's a tradeoff between speed and headway - at low speed the train takes longer to enter and leave platforms and pass other places. The exact answer depends on train length and acceleration but I think the optimum speed for maximum capacity is somewhere around 40-50mph.

The optimum for 12 coach trains, with 9%g braking, is actually just about 30mph.

 

[cle]

It could run tube-like between Farringdon and Blackfriars/London Bridge - with a sense of urgency rather than a trundle. I know distances are short, but they are on the tube and they don't just coast - they accelerate and decelerate.

Padding, dwell times, recovery - call it what you like, but the whole thing could be tightened. And as to tube-like use, yes some people have cottoned on, but it is not there yet. Each route will have a turn up and go service once at full push, even to West Hampstead (Kentish Town and Finsbury Park frequencies debatable) - I'd like to see this used as a metro as it absolutely has capacity. Crossrail will help this I'm sure.

 

[Bald Rick]

It could run tube-like between Farringdon and Blackfriars/London Bridge - with a sense of urgency rather than a trundle

Yes it could do. But then the tube doesn’t have to accommodate numerous other non-tube services outside the tube sections on a 100mile plus trip.

 

[DerekC]

The optimum for 12 coach trains, with 9%g braking, is actually just about 30mph.

Please explain - this seems counter to logic. The higher the speed the train can accelerate to as it moves off the platform, the sooner it clears the platform block and the sooner the next arriving train can enter. There is of course a plain line headway calculation to go with this, but at present we are talking about platform reoccupation (run in-run out) time.

 

[JN114]

Please explain - this seems counter to logic. The higher the speed the train can accelerate to as it moves off the platform, the sooner it clears the platform block and the sooner the next arriving train can enter. There is of course a plain line headway calculation to go with this, but at present we are talking about platform reoccupation (run in-run out) time.

Higher speeds require longer blocks - you have to factor in deceleration distance as well.

 

[tasky]

When the core section of Thameslink was being assessed for higher capacity there was a push to get the line speed increased from 30mph to 40 mph - not so much because of a reduction in sectional running times but because it would have helped reduce platform reoccupation time. But it ended up on the "too difficult" pile - largely (I think) because there was no real science behind the line speed in the first place, so nobody could show whether an increase would be safe or not. I think in retrospect it should have been pushed harder.

This is interesting, thanks

 

[computerSaysNo]

The ATO system which is going to be used in the core, will it be fixed block or moving block?

 

[cle]

Yes it could do. But then the tube doesn’t have to accommodate numerous other non-tube services outside the tube sections on a 100mile plus trip.

So timetable it to reality and passenger need, rather than reporting obligations and compensation/damage limitation?

 

[AM9]

So timetable it to reality and passenger need, rather than reporting obligations and compensation/damage limitation?

What does that mean?

 

[cle]

I think it's pretty clear - but in case you're genuinely unsure and not a disingenuous apologist (and I apologize if the former): Timetable according to optimized journey times, and honest arrival times and dwells. Less 'recovery' which is BS for padding, framed as operational and reliability driven, but is a mechanism against delay penalties first and foremost.

How about aiming for less delays overall, and tougher standard to aspire to - aka eating less rather than loosening a belt - same as induced demand for motorway lanes. Pad and that space will be comfortably filled by laxer ops.