Triple tracking

[talltim]

There seems to be a resistance in the UK to triple tracking as a capacity upgrade from double track. Many lines in the US with capacity issues seems to have been triple tracked in the last few years.
Obviously quadruple track has a higher capacity again, but costs more, and often there seems to be a need for more capacity, but not as much as quadruple track gives.
Does anyone know why it isn't more popular here? Is is due to disinclination to use bidirectional signalling?

 

[The Planner]

Bi-directional signalling and the fact it isn't an efficient use of capacity. It is a lot harder to timetable.

 

[Buttsy]

Would it work better if the middle track were bidirectional, or is that what you were thinking originally?

 

[talltim]

It could either be two monodirectional tracks and a central bidirectional, or all three bidirectional.
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Bi-directional signalling and the fact it isn't an efficient use of capacity. It is a lot harder to timetable.

I can understand it being more complicated to plan, but why do you consider three tracks a less efficient use of capacity than two?

 

[Crispy75]

It could either be two monodirectional tracks and a central bidirectional, or all three bidirectional.
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I can understand it being more complicated to plan, but why do you consider three tracks a less efficient use of capacity than two?

2 -> 4 tracks results in a 100% increase in capacity (assuming your stations and junctions are properly integrated)

2 -> 3 tracks does not result in a 50% increase, due to wasted time waiting for oncoming trains to clear before sending one in the other direction.

I suppose it might make sense on commuter lines, alternating the center track for morning and evening peaks, but you'd need extensive stabling at each end (or a through route) and therefore a large number of trains sitting around empty for most of the day. Symmetrical services are much easier to plan.

 

[LNW-GW Joint]

There is a 3rd track going in on 4 miles of the Shields Jn-Paisley line out of Glasgow Central. Was once 4-track, then reduced to 2 and now going to be 3.

Looks pretty complicated and expensive to me for a small capacity uplift.
Was linked with the intended Paisley-Glasgow Airport branch, which has been cancelled, but they decided to go ahead with the upgrade anyway.

Under the WCRM programme there was to have been a reversible 3rd track added to the WCML, also for about 4 miles, between Boar's Head and Balshaw Lane (reinstating the removed down slow). It would have kept freight and Northern's Liverpool-Blackpool trains off most of the main line between Wigan and Preston. This development figured regularly in the SRA strategy a few years ago and should have been built by now, but it seems to have been quietly dropped and doesn't even figure in the latest WCML RUS.

 

[Ploughman]

Can be seen in regular use between Mirfield and Ravensthorpe on the main Leeds - Huddersfield route were it mixes for a mile or 2 with the Calder valley line.
Outer tracks generally one way but centre line is BI DI mixing fast TPE services heading West with slow freight heading East and a couple of stopping services as well.

 

[AlterEgo]

A small portion of the WCML from Rugby to Nuneaton is also triple track.

 

[Bastiaan]

It can be useful on a stretch between a station and a junction a few miles further. Trains can leave the station quickly after each other, because departures can be regulated. Making sure every train arrives after each other is a lot more difficult, so by having a separate track for each direction, trains don't interfere with each other.

 

[asylumxl]

There is a bit of triple track around Wellingborough.

 

[The Planner]

2 -> 3 tracks does not result in a 50% increase, due to wasted time waiting for oncoming trains to clear before sending one in the other direction.

Exactly, you need a large enough margin for the exiting train to be clear then the entering train to be able to see greens (unless its approach controlled, which would be likely) on the approach. It isnt the same as flighting trains on headway.
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A small portion of the WCML from Rugby to Nuneaton is also triple track.

Yes, but it isn't bi-directional in normal use.
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There is a bit of triple track around Wellingborough.

That is a nightmare too, there are so few signals it is basically one train only in either direction.

 

[Bald Rick]

Assuming the additional track is on virgin land, the main reason is that the cost and effort in building a third track is approx 80% of that of building four. All the planning, design, consents and management costs are the same, signalling is arguably more expensive, the only saving is in civils, track and electrification.

In most cases adding two more tracks more than doubles (theoretical) capacity, as it enables trains of differing average speeds to be segregated.

In simple terms it is much better value for money to spend 100x on at least doubling capacity, than 80x on not even an extra 50%.

 

[asylumxl]

That is a nightmare too, there are so few signals it is basically one train only in either direction.

Since it's barely used is it that important?

 

[The Planner]

It is useful for chucking a freight out the way.

 

[DaveNewcastle]

There's a very well used stretch of triple track between Newcastle Station, through Manors Station, the site of the former Heaton station, through to Heaton Depot.
1 track is Down Main, 1 is Up Main and 1 is slow Bi-Di.
The slow line is busy with ECS movements between Newcastle and the Depot and for freight. It relieves the Mains from trafffic which otherwise would conflict and it seems to work well.
The only odd thing about the 3rd 'Slow' line is that it ends (rejoining the Mains) immediately outside Heaton Depot, so while it works well as 2 or 3 miles of a Bi-Di loop for freight, it doesn't keep ECS movements off the Mains entirely as they have to join the Up Main briefly just to get in and out of the Depot.

There's a much shorter length of 3 track between York Stn and Holgate Jn which doesn't help anybody. Its a bottleneck, and will be quadrupled shortly.

 

[Old Timer]

There seems to be a resistance in the UK to triple tracking as a capacity upgrade from double track. Many lines in the US with capacity issues seems to have been triple tracked in the last few years.
Obviously quadruple track has a higher capacity again, but costs more, and often there seems to be a need for more capacity, but not as much as quadruple track gives.
Does anyone know why it isn't more popular here? Is is due to disinclination to use bidirectional signalling?

The length of triple-tracking sections in the US is far longer than would ever be the case in the UK.

In some cases track same direction working on double lines is implemented to allow a faster (expedited) freight to pass a slower freight or indeed to allow an Amtrack service like the South Western Chief to pass slower running freight. Tripling simply allows that to be done without blocking trains running in the opposite direction.

For it to be feasible the section has to be long enough. In the US this can be done with ease outside of the Cities, in the UK it is a far more complex process that would require considerable expenditure on Infrastructure, once the extra land for the trackbed had been bought.

Unlike the US there is no large area of parallel land alongside the UK railway lines that can be used for this purpose.

 

[Crispy75]

Also, because the US network is so heavily biased towards freight, symmetrical services are not so important. It's pointless sending the same number of trains to and from a busy port, when the majority of its traffic is imports distributed around the country. When a ship comes in, the traffic is outbound. When there's no ship in port, the empty wagons can be sent back whenever there's spare paths.

(although this is a stronger argument in favour of single tracking)

 

[island]

There's a useful stretch of triple track for a few miles out of Heuston station in Dublin.

 

[WatcherZero]

Here a passing loop has the same benefit as three tracking but much shorter and cheaper.

 

[spionkop64]

Can be seen in regular use between Mirfield and Ravensthorpe on the main Leeds - Huddersfield route were it mixes for a mile or 2 with the Calder valley line.
Outer tracks generally one way but centre line is BI DI mixing fast TPE services heading West with slow freight heading East and a couple of stopping services as well.

Not entirely correct. The Bi-Di part is only between Mirfield East and LNW Junction and was put in to reduce the number of point ends and increase line speed over the junctions. If it was to be fully Bi-Di it would require a set of points at Heaton Lodge East to get east bound services onto the 'middle road'. TPE have suggested it, but it would have limited value, mainly because fast services overtake stopping trains on the up (west bound) lines. A catch 22 as has been eluded to elsewhere in this thread.

With TPE moving up to 5 per hour in the near future it simply would not work. The savings you make on the down (east bound) would be lost by dealys to up (west bound) services. That said it would be handy during times of disruption. Regularly TPE services are signalled onto the slow line to avoid problems on the fast line and vice versa with Northern services routed onto the fast to avoid issues on the slow (although Northern drivers regularly question being signalled onto the fast line which ruins the time potentially saved).