4 track railway: line pairings discussion

[sharpener]

Moderator note: split from

Report of collision Bedford (Elstow) - 19/06/26

Hearing reports of a collision between two trains at Bedford with one train now derailed

www.railforums.co.uk

As a general HF observation, from the cab ride video linked up thread the oncoming traffic on 4 lines paired by speed looks much more confusing than on 4 lines paired by direction as with the GN or SW main lines.

I assume this is historical, as in many places the pairs are quite a long way apart so I assume they were built at different times or even by different companies.

 

[AlterEgo]

As a general HF observation, from the cab ride video linked upthread the oncoming traffic on 4 lines paired by speed looks much more confusing than on 4 lines paired by direction as with the GN or SW main lines. I assume this is historical, as in many places the pairs are quite a long way apart so I assume they were built at different times or even by different companies.

Paired by speed so they go

Up
Down
Up
Down

Is generally better for signal sighting as there is less risk of reading across.

 

[John Webb]

....As a general HF observation, from the cab ride video linked upthread the oncoming traffic on 4 lines paired by speed looks much more confusing than on 4 lines paired by direction as with the GN or SW main lines. I assume this is historical, as in many places the pairs are quite a long way apart so I assume they were built at different times or even by different companies.

The Midland's 'London Extension' was built in two phases.

For the 1868 opening only the two current fast lines were built - I understand this was due to the cheapness of land, but the expense of steel rail!

An Up Goods line was added in stages to bring the East Midlands coal to London, as that was where their profit lay.

By the late 1880s they could afford to bring the line up to the planned four tracks, and did so around 1895, although the present slow lines remained goods lines from Bedford to south of St Albans City until 1906, when the goods lines became slow lines to north of Harpenden.

The goods lines only became the slow passenger lines from Harpenden to Bedford with the introduction of DMUs in 1959.

At a number of locations separate bridges were built in the 1890s for the newer tracks.

 

[edwin_m]

The Midland's 'London Extension' was built in two phases.

For the 1868 opening only the two current fast lines were built - I understand this was due to the cheapness of land, but the expense of steel rail!

An Up Goods line was added in stages to bring the East Midlands coal to London, as that was where their profit lay.

By the late 1880s they could afford to bring the line up to the planned four tracks, and did so around 1895, although the present slow lines remained goods lines from Bedford to south of St Albans City until 1906, when the goods lines became slow lines to north of Harpenden.

The goods lines only became the slow passenger lines from Harpenden to Bedford with the introduction of DMUs in 1959.

At a number of locations separate bridges were built in the 1890s for the newer tracks.

However, at Bedford they re-used their existing station which was built for their older route via Hitchin, which is why the Slow and Fast lines are separate south of the station and indirectly why the crossovers are so far away. In that area the original lines towards London must have been roughly where the Slows now are.

 

[Farnborough]

As a general HF observation, from the cab ride video linked up thread the oncoming traffic on 4 lines paired by speed looks much more confusing than on 4 lines paired by direction as with the GN or SW main lines.

The SWML is an interesting mix...

• South of Wimbledon it is, indeed, paired by direction (US UF DF DS)
• Just north of Wimbledon, they switch to pairing by speed (UF DF US DS)

I've often wondered why this is...

 

[MarkyT]

The SWML is an interesting mix...

• South of Wimbledon it is, indeed, paired by direction (US UF DF DS)
• Just north of Wimbledon, they switch to pairing by speed (UF DF US DS)

I've often wondered why this is...

Paired by speed/function is good for terminus approaches, as it splits the throat up and avoids trains having to cross the whole layout. Kings Cross is configured similarly, with a flyover near Holloway.

Historically, the main line side of Waterloo was paired by direction until the Wimbledon flyover was introduced in 1936, and routing trains across the throat was handled by the long multitrack crossovers known as West Crossings, which partially remain in the modern layout.

Kings Cross was also paired by direction right up to the station throat until the 1970s remodelling. There was a Holloway flyover before, but it was exclusively for up freights crossing to the goods yard and North London line connection. The 70s scheme rebuilt the flyover for slow line passenger services to cross to the suburban platforms without fast line conflicts.

Edit: 2nd para rewritten for clarity and accuracy.

 

[sharpener]

The SWML is an interesting mix...

• South of Wimbledon it is, indeed, paired by direction (US UF DF DS)
• Just north of Wimbledon, they switch to pairing by speed (UF DF US DS)

I've often wondered why this is...

Flyover was built in 1936, I am guessing from the style of the concrete construction the nearby signal box is about the same date.

Paired by speed/function is good for terminus approaches, as it splits the throat up and avoids trains having to cross the whole layout. Kings Cross is configured similarly, with a flyover near Holloway.

Conversely having the fasts in the middle makes it easier to build stations which serve only the slow lines, like Raynes Park or Berrylands. Cf Welham Green etc on the GN.

New Malden where I grew up actually does have centre platforms to serve the fast lines, but even 60 years ago only very occasional trains stopped there and AFAIK they have been disused for many years. The spacing of the tracks means that the bridge over the main road there is in fact two separate bridges which were renewed about a month apart.

ETA it also makes the burrowing junction for the Kingston branch (cf Stevenage) much easier than if one of the slows had to come up in the middle of the layout. But I also remember a discussion on here somewhere which says the original arrangement was not the same as it is now, which explains why there is an unused bore at the Elm Road underbridge.

 

[norbitonflyer]

Conversely having the fasts in the middle makes it easier to build stations which serve only the slow lines, like Raynes Park or Berrylands. Cf Welham Green etc on the GN.

New Malden where I grew up actually does have centre platforms to serve the fast lines, but even 60 years ago only very occasional trains stopped there and AFAIK they have been disused for many years. The spacing of the tracks means that the bridge over the main road there is in fact two separate bridges which were renewed about a month apart.

ETA it also makes the burrowing junction for the Kingston branch (cf Stevenage) much easier than if one of the slows had to come up in the middle of the layout. But I also remember a discussion on here somewhere which says the original arrangement was not the same as it is now, which explains why there is an unused bore at the Elm Road underbridge.

Indeed. paired by direction also makes it easier for trains to switch between fast and slow, as happens for example with trains which are first stop Surbiton, then all stations.

There are several burrowing and flying junctions - for the Epsom, Kingston, Hampton Court, Cobham New Line, Addlestone (west facing) Alton and Salisbury lines.

Indeed the only flat junction - with a regular passenger service on the branch - on the four track section between Waterloo and Worting Junction is at Woking. (Wimbledon and Weybridge have flat junctions, but no regular passenger services use them)

The curious arrangement at New Malden is because when the line was extended to New Malden from the original terminus at Kingston in 1869, both tracks passed under the main line and ran on the south side of the main line (ie paired by use) to Wimbledon, continuing to Tooting and ultimately Holborn Viaduct, as a joint operation with the LOndon Chatham & Dover Railway. The main line was quadrupled in 1884, and the present configuration of the junction dates from then.

A similar arrangment of redundant underpasses can be seen west of Turnham Green (best seen from trains to and from Richmond) where the former LSWR tracks from Richmond burrowed under the original District Railway's line to Ealing. This arrangment was built in 1911, when the line between there and Hammersmith was quadrupled, and again reconfigured when the Ealing line was quadrupled in the 1930s and the layout betweeen Turnham Green and Hammersmith converted from paired by use to paired by direction. (This also explains why Stamford Brook has only three platforms, with the eastbound District much newer than the other two)

 

[ClivePage]

I used to live in Woking and observed how convenient it was to have the fast lines in the centre and the slow lines on the outside. It was obviously faster (and safer) for trains to switch from fast to slow or vice-versa in either direction without having to wait for trains going the other way on some other track. But it was also more convenient for passengers waiting at stations with a pair of island platforms such as at Woking. Then if the fast train is delayed a bit one can simply walk over to the adjacent platform and get on the slow train instead, or vice-versa.

So I have long wondered why other 4-track routes, like London to Bedford, can't be reconfigured to do the same as it seems to give advantages to the railway system and to passengers. I realise that historically the Bedford route was built in two stages, but that was an awfully long time ago.

 

[sharpener]

The curious arrangement at New Malden is because when the line was extended to New Malden from the original terminus at Kingston in 1869, both tracks passed under the main line and ran on the south side of the main line (ie paired by use) to Wimbledon, continuing to Tooting and ultimately Holborn Viaduct, as a joint operation with the LOndon Chatham & Dover Railway. The main line was quadrupled in 1884, and the prTesent configuration of the junction dates from then.

They were fortunate that there was room on the N side of the embankement to bring the branch from Kingston up there instead. Maybe under the footpath there is a continuation of the MWB pipe track which certainly follows that alignment on the London side of the station?

I don't know what the actual gradient is but it was always surprising the way the trains from Kingston pop up seemingly "out of nowhere" at the up platform at NM station.

 

[zwk500]

There's an old thread that's relevant here:

Paired by use or paired by direction

On the West Coast route, between London* and where the Northampton route diverges at Roade, there are 4 tracks. These are paired by use so from East to West you have up slow, down slow, up fast and down fast. North of Rugby it is paired by direction, so from east to west you have down slow...

www.railforums.co.uk

== Doublepost prevention - post automatically merged: Today at 10:25 ==

I used to live in Woking and observed how convenient it was to have the fast lines in the centre and the slow lines on the outside. It was obviously faster (and safer) for trains to switch from fast to slow or vice-versa in either direction without having to wait for trains going the other way on some other track. But it was also more convenient for passengers waiting at stations with a pair of island platforms such as at Woking. Then if the fast train is delayed a bit one can simply walk over to the adjacent platform and get on the slow train instead, or vice-versa.

At Woking it is quite inconvenient that the terminating train must cross to the middle of the through tracks, and a similar problem occurs at Basingstoke. If both had been paired by use then terminating trains would be able to leave one set of lines alone, and you'd also have less conflicts from Up Portsmouth trains at Woking and Down Reading trains at Basingstoke.

So I have long wondered why other 4-track routes, like London to Bedford, can't be reconfigured to do the same as it seems to give advantages to the railway system and to passengers. I realise that historically the Bedford route was built in two stages, but that was an awfully long time ago.

For many lines, the advantage of alternate running (paired by use) is that terminating stations and junctions can be configured to have no interaction with the fast/main lines. This is especially important where you have high speeds, because the signalling may require additional protection (e.g. double reds) and the impact of being checked down to a red from 125mph is far worse than being checked down from 60mph. Compare Tring on the WCML with Welwyn Garden City on the East Coast Main Line.

Where switching between fast and slow lines is more common, some lines transition between the two configurations - e.g. the WCML is paired by use south of Rugby, but paired by direction through the station and up to Colwich Jn. Interestingly at 2 places on the WCML the Down fast is outside the Down Slow, for deconfliction reasons - Rugby to Brinklow and Hartford Jn to Acton Bridge.

The primary reason why lines generally haven't been reconfigured since is the cost of rebuilding the lines where the Up Slow now needs to become the Down Fast, or similar.

 

[norbitonflyer]

For many lines, the advantage of alternate running (paired by use) is that terminating stations and junctions can be configured to have no interaction with the fast/main lines. This is especially important where you have high speeds, because the signalling may require additional protection (e.g. double reds) and the impact of being checked down to a red from 125mph is far worse than being checked down from 60mph. Compare Tring on the WCML with Welwyn Garden City on the East Coast Main Line.

Which is why there is a flyover at Welwyn, for example

I used to live in Woking and observed how convenient it was to have the fast lines in the centre and the slow lines on the outside. It was obviously faster (and safer) for trains to switch from fast to slow or vice-versa in either direction without having to wait for trains going the other way on some other track. But it was also more convenient for passengers waiting at stations with a pair of island platforms such as at Woking. Then if the fast train is delayed a bit one can simply walk over to the adjacent platform and get on the slow train instead, or vice-versa.

It doesn't work at Woking, I'm afraid, because the layout is not two islands, but one island serving both fast lines, and two side platforms serving the slow lines (and a bay in the island for the stoppers). So if you need to change from fast to slow or vice versa you have to cross the bridge, unless you are changing to/from the all-shacks.
Putting the bay in the middle at least means a train using it doesn't have to find a gap in both fast lines at the same time.

 

[sharpener]

So I have long wondered why other 4-track routes, like London to Bedford, can't be reconfigured to do the same as it seems to give advantages to the railway system and to passengers. I realise that historically the Bedford route was built in two stages, but that was an awfully long time ago.

The primary reason why lines generally haven't been reconfigured since is the cost of rebuilding the lines where the Up Slow now needs to become the Down Fast, or similar.

In addition to all the S&C work required you would need to resignal everything. But the main objection is surely the length of time you would have the entire railway out of action. You can't simply do it over a weekend with an army of navvies, as the conversion from broad to standard gauge was reputedly done in some places. If you did it piecewise the temporary works at the end of the sections would be horrendous.

 

[Western Sunset]

Between Soton Cent and Millbrook, the fast lines are on the outside with the slows (serving the island platform at Millbrook) in the centre.

 

[zwk500]

Between Soton Cent and Millbrook, the fast lines are on the outside with the slows (serving the island platform at Millbrook) in the centre.

And delightfully, freight on both sides 'outside' the fast lines!

 

[MarlowDonkey]

The SWML is an interesting mix...

• South of Wimbledon it is, indeed, paired by direction (US UF DF DS)

The London Underground 4 track sections use US UF DF DS between Barons Court and Acton Town (Picadilly fast, District slow). Between Finchley Road and Neasden it's the other way round (UF US DS DF) with the fasts being the Metropolitan and the slows the Jubilee. In both cases though it's the big trains on the outside and the small ones in the middle.

When what was then the Bakerloo was extended from Baker Street to Stanmore in the 1930s, they rebuilt some of the stations to have an island platform in the middle which accounts for the art deco styling of some of them despite the original line and stations dating back to Victorian or Edwardian times.

 

[edwin_m]

I used to live in Woking and observed how convenient it was to have the fast lines in the centre and the slow lines on the outside. It was obviously faster (and safer) for trains to switch from fast to slow or vice-versa in either direction without having to wait for trains going the other way on some other track. But it was also more convenient for passengers waiting at stations with a pair of island platforms such as at Woking. Then if the fast train is delayed a bit one can simply walk over to the adjacent platform and get on the slow train instead, or vice-versa.

So I have long wondered why other 4-track routes, like London to Bedford, can't be reconfigured to do the same as it seems to give advantages to the railway system and to passengers. I realise that historically the Bedford route was built in two stages, but that was an awfully long time ago.

London to Bedford would need flyovers somewhere in North London, south of Luton and south of Bedford. It would also need multiple rebuilds of stations and the tracks either end of them (where there are often bridges too) because the current Fasts are straight and the Slows dogleg out with a speed restriction.

It doesn't work at Woking, I'm afraid, because the layout is not two islands, but one island serving both fast lines, and two side platforms serving the slow lines (and a bay in the island for the stoppers). So if you need to change from fast to slow or vice versa you have to cross the bridge, unless you are changing to/from the all-shacks.
Putting the bay in the middle at least means a train using it doesn't have to find a gap in both fast lines at the same time.

In the absence of any grade separation, a bay in a centre island is less disruptive operationally than one off to one side, as it only needs a gap in the Down Fast service when a terminator arrives and in the Up Fast when it departs. A side bay needs a gap in both Fasts at the same time either on arrival or on departure. If you have to have a side bay then it's better to have it so the crossing move takes place on arrival, because if the arriving train is delayed it will probably have enough turnback time to recover, whereas a delay on departure causes lateness down the line. This arrangement also means that originating and through trains in the same direction go from the same side of the station, which also reduces the crossing-the-bridge problem.

If they ever build the Woking flyover they could put a turnback somewhere around Worplesdon so trains could terminate there and return to the Up Slow without touching the Fasts.

The London Underground 4 track sections use US UF DF DS between Barons Court and Acton Town (Picadilly fast, District slow). Between Finchley Road and Neasden it's the other way round (UF US DS DF) with the fasts being the Metropolitan and the slows the Jubilee. In both cases though it's the big trains on the outside and the small ones in the middle.

When what was then the Bakerloo was extended from Baker Street to Stanmore in the 1930s, they rebuilt some of the stations to have an island platform in the middle which accounts for the art deco styling of some of them despite the original line and stations dating back to Victorian or Edwardian times.

Having the Slows in the middle allows their trains to turn back without touching the Fasts or needing grade separation, although it's a bit moot in this case because if the Slows were outside then Wembley Park terminators could turn back on the Stanmore line as I suggested above for future Woking. It does create another alignment problem though, as the Fasts have to dogleg out to make space for each station - not so much of an issue on the Met as line speeds are modest.

 

[Magdalia]

So I have long wondered why other 4-track routes, like London to Bedford, can't be reconfigured to do the same as it seems to give advantages to the railway system and to passengers.

In the case of London-Bedford, there would be major disadvantages.

Most important is the requirement to terminate and start slow line trains part way along the route at St Albans City and Luton. The former has a turnback siding, between the down and up slow lines. The latter has an additional platform, with platform 3 the down slow, platform 1 the up slow, and terminating trains using platform 2 in between. With a paired by direction layout both would require flyovers to allow terminating or starting trains to cross the fast lines.

Another factor is location of carriage sidings. Paired by direction would have major implications for movements onto the carriage sidings at both Cricklewood and Bedford.

 

[MarkyT]

London to Bedford would need flyovers somewhere in North London, south of Luton and south of Bedford. It would also need multiple rebuilds of stations and the tracks either end of them (where there are often bridges too) because the current Fasts are straight and the Slows dogleg out with a speed restriction.

In the absence of any grade separation, a bay in a centre island is less disruptive operationally than one off to one side, as it only needs a gap in the Down Fast service when a terminator arrives and in the Up Fast when it departs. A side bay needs a gap in both Fasts at the same time either on arrival or on departure. If you have to have a side bay then it's better to have it so the crossing move takes place on arrival, because if the arriving train is delayed it will probably have enough turnback time to recover, whereas a delay on departure causes lateness down the line. This arrangement also means that originating and through trains in the same direction go from the same side of the station, which also reduces the crossing-the-bridge problem.

A side bay on the opposite side may be blocked by an opposing direction out of course movement which might then delay other trains following the terminator. On a 4 track layout a way to address that is to place additional fast crossovers a section further back on approach so the slow terminator can turn right early and wait on the same direction fast, like a middle turn lane, while other fast traffic in the same direction can weave around it using the parallel slow; some small loss of speed and time perhaps for those trains, but much better than stopping and waiting for the terminator to move.

A bay on the same side can't be blocked by other traffic on arrival, which may be useful for making tight onward connections, but departures need a clear margin between trains in both directions.

If they ever build the Woking flyover they could put a turnback somewhere around Worplesdon so trains could terminate there and return to the Up Slow without touching the Fasts.

Having the Slows in the middle allows their trains to turn back without touching the Fasts or needing grade separation, although it's a bit moot in this case because if the Slows were outside then Wembley Park terminators could turn back on the Stanmore line as I suggested above for future Woking. It does create another alignment problem though, as the Fasts have to dogleg out to make space for each station - not so much of an issue on the Met as line speeds are modest.

They can turn elsewhere, even if that's not a regular or frequent occurrence. Carto Metro shows middle sidings at West Hampstead and Willesden Green. Trains can terminate at Neasden too but I assume that means going empty into the yard and crossing the London bound Met.

With slows on the outside, Wembley terminators might use the existing depot flyunder to swap sides instead.

An advantage of slows in the middle is a single island platform can contain all facilities and staffing. Likely a lower overall construction, operation and maintenance cost than two individual side platforms.

 

[Dr Hoo]

Still on the MML, the freight terminals south of Kettering are all on the ‘slow’ side - Wellingborough, Elstow, Limbury Road, Crescent Road and Radlett. This makes serving them much easier.

Meanwhile, Mountsorrel is on the ‘fast’ side and a right pain for long-distance passenger services.

 

[yorkie]

So I have long wondered why other 4-track routes, like London to Bedford, can't be reconfigured to do the same as it seems to give advantages to the railway system and to passengers. I realise that historically the Bedford route was built in two stages, but that was an awfully long time ago.

Huge cost, which wouldn't be recovered from benefits for many decades. However if anyone would like to discuss whether it may be possible or theoretical benefits, please create a new thread in the Speculative Discussion section.

 

[Henffordd]

In addition to all the S&C work required you would need to resignal everything. But the main objection is surely the length of time you would have the entire railway out of action. You can't simply do it over a weekend with an army of navvies, as the conversion from broad to standard gauge was reputedly done in some places. If you did it piecewise the temporary works at the end of the sections would be horrendous.

This raises a question for me: how did SR create the Wimbledon flyover in 1936, and with what level of disruption? Perhaps for the history section?

And a follow-on: given the concrete flyover is now 90 years old, for how long will it continue to be safe?

 

[Magdalia]

Kings Cross was also paired by direction right up to the station throat until the 1970s remodelling. There was a Holloway flyover before, but it was exclusively for up freights crossing to the goods yard and North London line connection. The 70s scheme rebuilt the flyover for slow line passenger services to cross to the suburban platforms without fast line conflicts.

Which is why there is a flyover at Welwyn, for example

Until electrification in the 1970s Kings Cross operated with traditional arrivals and departures sides. Furthermore, the tracks to and from the Widened Lines were on the outside. The station throat was also paired by direction!

The flyover at Welwyn also dates from the 1970s remodelling.

Paired by direction suits the ECML because of the 2 track sections at Digswell and Holme. Both would operate at much lower capacity if the 4 tracks either side were paired by use. Historically, the ECML had many more 2 track sections at New Barnet-Potters Bar, Arlesey, Sandy and Huntingdon. The first of these was 4 tracked in the late 1950s, the others also in the 1970s.

 

[renegademaster]

Other than the Met Line/Chiltern line section through Northwest London is there any other cases of Slows on the inside and fasts going around it?

 

[zwk500]

Other than the Met Line/Chiltern line section through Northwest London is there any other cases of Slows on the inside and fasts going around it?

As mentioned above, Southampton to Milbrook. Half-cases on the WCML from Rugby to Brinklow and Hartford Jn to Acton Bridge, both with the Down Slow inside the Down Fast but the Up Slow outside the Up Fast so tracks are DF-DS-UF-US.

 

[swt_passenger]

This raises a question for me: how did SR create the Wimbledon flyover in 1936, and with what level of disruption? Perhaps for the history section?

And a follow-on: given the concrete flyover is now 90 years old, for how long will it continue to be safe?

A 1949 OS map shows a fairly detailed track layout with only a slight, albeit significant difference to today’s layout. There was still an empty space wide enough for at least a temporary up slow, all the way past the relatively new flyover including the ramps, it would have been on the west side. My thinking is that they would have slewed the up slow over to the west, then put the two fast lines into their future alignment, as they are today. That would have provided space to build the flyover and its ramps with no impact on the down slow at all.

 

[Dr Hoo]

This raises a question for me: how did SR create the Wimbledon flyover in 1936, and with what level of disruption? Perhaps for the history section?

And a follow-on: given the concrete flyover is now 90 years old, for how long will it continue to be safe?

Amazingly the switch was done over a weekend when Waterloo-Wimbledon was re-signalled! Obviously with a lot of preparation. New signals sitting ‘bagged up’, switch on, ‘bags off’ and away you go.

 

[Belperpete]

Surprised nobody has mentioned Gloucester Road Junctions, with it's flying junctions to interface the lines from London Bridge, Victoria and East Croydon/Brighton which were all 4 track (or more), but all paired differently!

Extra flying junctions were added in the 1980s, when the lines to East Croydon were reconfigured.

 

[Falcon1200]

Other than the Met Line/Chiltern line section through Northwest London is there any other cases of Slows on the inside and fasts going around it?

IIRC part of the Lancashire & Yorkshire Railway's route between Manchester and Wigan was arranged like this, however no longer 4 tracked of course!

 

[Vexed]

I don't think anyone's mentioned maintenance yet, which can be less disruptive on paired by use (US DS UF DF) as one the fast or slow lines can be taken for a possession overnight/early morning/late evening and everything can run on the other pair that's still open.

Particularly important on the south MML with 24/7 passenger services, though the WCML and GWML are still pretty active with freight overnight too and generally have platforms on both pairs.

However this does mean you can't save cost by only building platforms on the slow lines.