Bi-directional signalling and critisism of single track sections

 
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
I have read before that single track sections have been seen as major bottlenecks, limiting the frequency of trains that can be run and amplifiying the effects of delays. But I realise that most of our single track sections have stations without passing loops, demanding trains to stop on a single track section. For example, the Altona loop has Seaholme, Altona and Westona stations, but a passing loop only at the latter.

Is it possible that single track sections might not be such a bottleneck if there were passing loops at all stations? I guess that single track, with passing loops at most or all stations is used in some other countries, such as Japan, without leading the the disruptions that we have here.

On a related note, are there any double track sections with bi-directional signalling. This enable single line working, if say something goes wrong on one track, it could occasionally allow trains to leapfrog.

Sponsored advertisement

  awsgc24 Minister for Railways

Location: Sydney
Extra crossing loops enables:
* More trains, OR
* Reduced delays at loops waiting for opposing trains to clear single line.
* But you cannot get 100% of both,

* The single line sections should be reasonably equal time-wise.
* Ideally the loops should be at stations, but can be between stations. Think old Lilydale line before full duplication.
* Island platforms are generally better than side platforms, since you can switch island platforms easily, passenger-wise.

* While crossing loops can be as short as a train, there is something to be said in having longer loops with high speed turnouts, so that an arriving train clears the single line at maximum speed with minimum delay to the waiting departing train.
* Simultaneous arrival into the loop, may require catchpoints, or intermediate timed trains stops; or a more advanced ATP system.

If the remaining single line section shrink in size, double line may be installed, like "Passing Lanes", which saves turnouts and signals.

A mixture of single and double lines may avoid expensive infrastructure like tunnels and viaducts, like on Hurstbridge line.

If long freight trains run, longer than the short loops, freighters must arrive second, and leave first, which causes delays to short passengers which must be held in the loop.
* Two long trains cannot cross at a short loop. Think of Nowra line.
  712M Chief Commissioner

If you were going to go to the expense of rebuilding stations to add a passing loop, you might as well spend a little bit more and duplicate the whole line. The Belgrave line beyond Ferntree Gully has a similar setup to what you describe; Tecoma being the only station with a single platform. Whilst it allows a 10 minute frequency to be run, it leaves no room for delays. A 5 minute delay to one train at the start of peak hour can cause everything to run behind schedule until the end of the peak. This results in some runs being truncated at Upper Ferntree Gully.

The Werribee line is signalled for two-way running from Newport South all the way to Geelong which is occasionally utilised during disruptions but for normal day-to-day operations only left-hand running is used within the suburban area. The City Loop is of course bi-directionally signalled as well as the up line between Camberwell and Riversdale and the double track sections of the RFR corridors Sunbury-Bendigo, Pakenham-Moe and Rockbank-Ballarat.

The centre lines from Caulfield to Moorabbin and Burnley to Box Hill are also signalled for two-way running.
  railblogger Chief Commissioner

Location: At the back of the train, quitely doing exactly what you'd expect.
On a related note, are there any double track sections with bi-directional signalling. This enable single line working, if say something goes wrong on one track, it could occasionally allow trains to leapfrog.
Myrtone
The RFR lines have bi-directional signalling. Not sure if there are any in the suburban area.
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Extra crossing loops enables:
* More trains, OR
* Reduced delays at loops waiting for opposing trains to clear single line.
* But you cannot get 100% of both,

* The single line sections should be reasonably equal time-wise.
* Ideally the loops should be at stations, but can be between stations. Think old Lilydale line before full duplication.
* Island platforms are generally better than side platforms, since you can switch island platforms easily, passenger-wise.

* While crossing loops can be as short as a train, there is something to be said in having longer loops with high speed turnouts, so that an arriving train clears the single line at maximum speed with minimum delay to the waiting departing train.
* Simultaneous arrival into the loop, may require catchpoints, or intermediate timed trains stops; or a more advanced ATP system.
awsgc24


I've heard of two single track sections on the Sydney suburban, since you live there, can you describe them in relation to what you say they should be? Are they any more reliable than the ones in Melbourne? `

It does seem like a good idea for the loop to be at least a little longer than the train

A mixture of single and double lines may avoid expensive infrastructure like tunnels and viaducts, like on Hurstbridge line.
awsgc24


But remember that the cost of the infrastructure is not ongoing. I'm guessing that those sections of the Hurstbridge line were built long ago are single track to this day just to save the cost of building all those decades ago.

If long freight trains run, longer than the short loops, freighters must arrive second, and leave first, which causes delays to short passengers which must be held in the loop.
* Two long trains cannot cross at a short loop. Think of Nowra line.
awsgc24


This suggests that twinned-single track,* double track, triple track (centre track for freight trains except when passing other freight trains) or two or more tracks per direction is better suited to mixed passenger and freight traffic.

*Twinned single track is where trains travel in both directions on both tracks, with passing loops on both sides. In case of mixed passenger and freight traffic, it might be one track for passenger trains and the other for freight. I've heard of cases of it, but only where each track is a different gauge.
  woodford Chief Commissioner

The Albury line North of Seymour is signaled for bidirectional running and this is regularly used.
  awsgc24 Minister for Railways

Location: Sydney
I've heard of two single track sections on the Sydney suburban, since you live there, can you describe them in relation to what you say they should be? Are they any more reliable than the ones in Melbourne? `
Myrtone
SINGLE LINES IN SYDNEY

In Sydney, the Clyde-Carlingford branch is double from Clyde to Rosehill (exclusive). But the double line is all at one end, and not in the middle of the line. An extra loop was proposed, but never built under the Clearways project. Also the round trip running time is a bit more than 30 minutes, so that it is not possible to connect with 30 minute interval trains on the main line. Also, Clyde is a low patronage station with poor connecting, unlike say Granville and Lidcombe. Much better to convert it to light rail, with extra duplication, as part of a Parramatta-Carlingford-Eastwood- Macquarie Uni line.

In Sydney, the Sutherland-Cronulla branch was opened in 1938 as single line, with left hand running loops and island platforms at Gymea and Caringbah. The loops could operate automatically without CTC, though this could lead to "snookers" if two up trains tried to cross two down trains at any loop. Around 1980, Gymea-Caringbah was duplicated with CTC installed. This reduced but did not eliminate delays waiting for 4 per hour trains to clear the single. Generally counter-peak trains were made to wait. Off peak trains at 2 per hour, crossed in the middle of the double line at Miranda. Gymea and Caringbah loops had simultaneous arrivals with intermediate timed train stops, later converted on part duplication to catchpoints.

In Sydney, the Blacktown-Richmond line was single line with loops at
* Quakers Hill (side platforms converted to island with electrification; simultaneous arrivals with timed intermediate trainstops)
* Riverstone (single platform with 2nd side platform later)
* Mulgrave (island platform)
* Windsor (side platform with no platform on loop; short siding used at "loop" ; no longer a crossing place)
* Clarendon (side platform with siding used as "loop"; converted to side platforms after electrification)

When the Blacktown-Riverstone section was electrified, a dock platform was provided for the connecting 2 or 4 car diesel train.

After full electrification, Riverstone, Mulgrave and Clarendon converted to simultaneous arrival with left hand running and catchpoints. NSWR likes catchpoints on running lines.

Duplication occurred first to Marayong (exclusive), extended to Quakers Hill, and further extended to Schofields relocated say 1000m closer to Sydney.

The single line sections on thus line are about the same 7-8 minutes, which allows a 15-minute 4 train per hour in the peak.

In the off peak, a 30-minute service uses every other loop. If a down train is late, it can use the empty loops and run 15 minutes late all the way to the end of the line at Richmond. Before the Clarendon loop was rebuilt, late running down trains had to be terminated in the middle of nowhere at Mulgrave. A letterwriter to the local paper could not see the value of the new loop at Clarendon, which is also in the middle of nowhere, and thought that the $6m cost was a complete waste of money. Such is the public's understanding of railway timetables. The loops at Clarendon and Mulgrave are timetabled once a day to clean the rails; they are mainly there for special extra trains and for late running.

On Richmond Air Base show days, (near Clarendon), the single line between Clarendon and Richmond is used to stable trains. Replacement buses are provided Clarendon to Richmond.
  mm42 Chief Train Controller

Los Angeles almost never has bustitution on its subway or light rail lines, because it is designed with bidirectional signalling and crossing points so a service can be delivered every 20 minutes if one track is out of action.  Surely this is better for passengers than bustitution, and much easier to organise.  Why can't we learn from this aspect of LA ?  

Even  pedestrian deaths in LA they close only one of the 2 tracks, with 20-minute train services moving past slowly on the other track. Somehow in Melbourne if there are 4 tracks the emergency services need all of them, and will quickly close the quad track between South Yarra and Caulfield to all services, even though their investigation only relates to one of the tracks.
  awsgc24 Minister for Railways

Location: Sydney
Los Angeles almost never has bustitution on its subway or light rail lines, because it is designed with bidirectional signalling and crossing points so a service can be delivered every 20 minutes if one track is out of action.  Surely this is better for passengers than bustitution, and much easier to organise.  Why can't we learn from this aspect of LA ?  
mm42
BIDIRECTIONAL IN NSW
* Waterfall to Unanderra - signalling in reverse direction is sparser than signalliing in normal direction. Track centres are mostly 3.66m (12 feet) so work on one track requires at least partial closure of other track.

* Epping to Chatswood - spare signals in reverse direction ; sparse crossovers; tracks in separate tunnels hence very wide centres.

* Blacktown to Schofields - parallel signals on both tracks; some wide centres, but not all wide, seem to be wider than 4m (the new standard)

SAVES CROSSOVERS
Down trains from Harden to Cowra branch run wrong line from Harden to Demondrille junction.

REFUGES ON DOUBLE LINE
A number of places use BiDi for about 2km to allow 1500m trains to refuge on one of the main lines. Cheaper than providing 3rd track, but assumes that traffic on main lines is sparse.
* Goulburn (900m)
* Wyong
* Cootamundra North
* Harden
* Glenlee to Menangle.
* Farley to Singleton/Muswellbrook (IIRC) ; new 3rd track is unidirectional.
* Passing lanes between Junee and Melbourne
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Do subway trains in LA have doors on the ends of each multiple unit train, like those on trains in Sydney?
  awsgc24 Minister for Railways

Location: Sydney
The capacity of a single line railway is increased if you "flight" the trains; say two Ups, two Downs, then two Ups again. However this makes the service intervals uneven, say 3 then 12 then 3 then 12 minutes again. Several intermediate block signal are also required to provide 3 minute following headway. However, passengers would generally prefer service intervals to be even, say 7, 8, 7, 8. With flighting, the crossing loops need to long enough to hold two trains, something like a "Passing Lane" with intermediate home signals. Most PL in NSW do not have such intermediate home signals, Yerong Creek being an exception in one direction. Cannot speak for the PL in Victoria.

By the time you build longer loops at existing sites, you may as well have new crossing loops half way between existing loops. Such loops do not have to be at stations, assuming that you have CTC to control the points and signals. In NZ, on the single track on the Johnstonville line, the first loop from Wellington is at a non-passenger location. Similarly at at least one loop on the Adelaide to Belair line.
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
The capacity of a single line railway is increased if you "flight" the trains; say two Ups, two Downs, then two Ups again. However this makes the service intervals uneven, say 3 then 12 then 3 then 12 minutes again. Several intermediate block signal are also required to provide 3 minute following headway. However, passengers would generally prefer service intervals to be even, say 7, 8, 7, 8. With flighting, the crossing loops need to long enough to hold two trains, something like a "Passing Lane" with intermediate home signals. Most PL in NSW do not have such intermediate home signals, Yerong Creek being an exception in one direction. Cannot speak for the PL in Victoria.
awsgc24

Trains on the City loop are in fact flighted during weekdays (except on the Clifton Hill loop), but all trains run in one direction in each tunnel for one half the day and in the other direction on the other half of the day, thus being in keeping with asymmetry in demand.

Somehow in Melbourne if there are 4 tracks the emergency services need all of them, and will quickly close the quad track between South Yarra and Caulfield to all services, even though their investigation only relates to one of the tracks.
mm42

And somehow we also need four tracks wherever (limited) express trains may pass all stations trains (such as East Richmond). But if express trains aren't scheduled to pass each other in those places, than one track run in each direction and a third track shared between both directions might be sufficient. For example, if all platforms are outside the tracks, then either the track on the left or that on the right would be allocated to all stations trains, and the centre track to express trains. On the occasion that two express trains need to pass one another, either they might both also have the nearside track allocated to them, or the train due to overtake another will have the centre track allocated to it.
  Nightfire Minister for Railways

Location: Gippsland
And somehow we also need four tracks wherever (limited) express trains may pass all stations trains (such as East Richmond). But if express trains aren't scheduled to pass each other in those places, than one track run in each direction and a third track shared between both directions might be sufficient. For example, if all platforms are outside the tracks, then either the track on the left or that on the right would be allocated to all stations trains, and the centre track to express trains. On the occasion that two express trains need to pass one another, either they might both also have the nearside track allocated to them, or the train due to overtake another will have the centre track allocated to it.
Myrtone
Express train negotiating turnouts to access a bypass or overtaking track will kill their express time saving.

The planets would also nearly need to align for a express train to overtake a slow train on a set track to give a set timetable outcome !  

Though I can be done, but factors such as

Traffic density.
Timetable expectations.
Track layout (crossovers, turnouts, platforms etc)
Traffic control, signalling systems.  
Safety requirements.

Will determine what can and what can not be done.
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Turnouts can be designed to be negotiated at full speed as is common on high speed railways. If say, a limited express service shares some section of track with another all stations service, and not the rest, and (limited) express trains only tend to pass each other on the track not shared with the other route, than three tracks may be sufficient where they do. They may still be sufficient if, should two express trains need to pass each other, only one of them is to overtake an all stations train.
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
I've found a page about bi-directional signalling on the Metrorail, and it mentions a triple track railway in NYC (the Flushing line) which does in fact have a centre track for use by express trains one way in the morning, and the other way in the afternoon.
  Heihachi_73 Chief Commissioner

Location: Terminating at Ringwood
Why can't we learn from this aspect of LA ?
mm42
Because our government learned the other aspect of LA instead: Freeways, toll roads and accompanying peak hour gridlock.

Sponsored advertisement

Subscribers: awsgc24, Myrtone, Nightfire

Display from:   

Quick Reply

We've disabled Quick Reply for this thread as it was last updated more than six months ago.