Cross River Rail will soon be completed.

Just as the 1990s quadruplication of the CBD lines established capacity for a couple of decades to come, so does CRR. However, to fully utilise this new capacity will likely require additional infrastructure. In this document we will try to explore what it would take to do so.

Beyond service increases on existing tracks, there are two new branch lines and two extensions of existing lines which seem both likely and desirable, having appeared in previous official planning documents. These are:

  • The Sunshine Coast line to at least Caloundra along the “CAMCOS” corridor;
  • The Flagstone-Beaudesert line generally following the existing interstate line;
  • Gold Coast line extension to Coolangatta;
  • Springfield line extension to Ripley.

Additionally the North-West Transport Corridor (NWTC) remains unused and potentially available for rail. Recent community survey work undertaken by Brisbane City Council underscores public support for rail in that corridor - though perhaps no longer above ground.

Terminology

Sectorisation

An important aspect of reliability is keeping delays on one line from cascading to other lines. At one extreme, all lines share tracks through the core of the network. At the other, each line has its own dedicated, independent tracks. SEQ lies in between: several branch lines are each grouped to an independent track pair (“sector”) through the Brisbane CBD - which at least keeps delays from cascading between groups.

Sectorisation in SEQ will necessarily be imperfect due to freight, but that can generally be timetabled outside of peak hours.

Through-routing

In contrast with, say, Adelaide, the SEQ network is mostly through-routed: trains which came from one line continue through the city as trains going to another line. This can increase efficiency: there’s no change of direction, and the time it takes to traverse the city is split between both lines.

Junctions

When train lines meet, there are two main ways to connect them. Most common is the flat junction. This is like a regular intersection on a road in the sense that turning right can obstruct oncoming vehicles. This has capacity and reliability issues. Most older junctions on the network are flat.

The flying junction is less common, and more like a freeway ramp: turning right doesn’t block oncoming vehicles. Flying junctions are therefore preferred for new construction.

Starting point: the network in 2026

Once Cross River Rail is complete, there will be three pairs of tracks through the city: the CRR tracks, the “mains” track pair (platforms 5 and 6 at Central) and the “suburbans” track pair (platforms 1/2 and 3/4 at Central).

Each train line will be assigned to one of those three track pairs or “sectors”, a process largely driven by network layout.

  1. The Caboolture-Nambour and Redcliffe lines in the north will pair with the Beenleigh and Gold Coast lines in the south, running via Cross River Rail.
  2. The Shorncliffe, Airport and Doomben lines in the northeast will pair with the Ipswich-Rosewood and Springfield lines in the southwest, running on the “mains”.
  3. The Ferny Grove line in the northwest will pair with the Cleveland line in the southeast, running on the “suburbans”. Some additional trains will run between Bowen Hills and Park Road to maintain a higher level of service to the inner southern stations.

There are several factors that result in this arrangement.

Track layout overview in 2026

Let’s consider the track topology, north to south.

Petrie station features a flying junction as the Redcliffe line splits off from the main northern tracks to Caboolture and beyond.

At Northgate station, the main northern tracks meet the Shorncliffe line in a flat junction. Southwest of Northgate on the combined section, there are four tracks: the Shorncliffe line takes the eastern pair, and the others run express on the western pair.

Just north of Eagle Junction, the Airport and Doomben lines separately branch off (both with flat junctions). These join the Shorncliffe line on the eastern track pair.

At its northern end, Cross River Rail surfaces in the Exhibition loop. Thus the CRR tracks meet with the existing four tracks between Bowen Hills and Albion stations. In a simple arrangement, the two tracks on the western side of the corridor (platforms 3 and 4 at Albion) connect with CRR, and the two tracks on the eastern side of the corridor (platforms 1 and 2 at Albion) continue to Bowen Hills.

The Ferny Grove line branches off just north of Bowen Hills station. It has a flying junction connected to the eastern track pair (the “suburbans”).

Just south of Roma Street station, the Merivale Bridge tracks branch off the “suburbans”. As this is a flat junction, this means that despite four tracks continuing all the way to Darra, it’s a bit tricky to run western-line trains on the suburbans.

At Park Road, the Cleveland line and the Beenleigh / Gold Coast lines meet. Without Cross River Rail, that’s a flat junction - possibly the busiest on the network.

At the southern end of the tunnel, the CRR tracks surface between Park Road and Dutton Park. In 2026, all QR trains in normal passenger service that pass through Dutton Park will go via Cross River Rail. With only three tracks through Dutton Park, running some trains from the south via CRR and some via the Merivale Bridge would not be reliable at scale.

The Tennyson connection between the southern and western lines is also a flat junction at both ends. This and sectorisation issues make it difficult to serve relative to the benefits.

West of Darra, we find another flying junction as the Springfield line splits off from the western tracks to Ipswich and beyond. This junction connects to the more eastern of the two track pairs.

Next steps

Making the most of what we already have: upgrades to existing lines

The Cleveland line past Manly is the most impactful single-track part of the network within metropolitan Brisbane. This limits frequency on the line, has substantial reliability implications, and also restricts timetabling elsewhere. Duplicating the line must be a top priority for investment once CRR is completed.

The entire Doomben line is also single-track. Targeted duplication efforts here will be needed to get peak frequency to a turn-up-and-go standard.

The Airport line can currently maintain 15 minute frequency despite its extensive single track section, but it does impose some timetabling constraints: Airport line trains must presently cross at its junction and at International station.

The Shorncliffe line (as of 2023) is still single track between Sandgate and Shorncliffe. Completing the duplication here will improve reliability and enable future service increases.

Continuing duplication and realignment north of Beerwah will not only benefit passenger rail for the Sunshine Coast Hinterland, but also freight and long-distance passenger services.

Finally, continuing works to make all stations accessible are both a community expectation and a legal requirement.

Gold Coast and Flagstone-Beaudesert

The broader corridor around the Mt Lindesay Highway is one of SEQ’s major growth areas with the Greater Flagstone priority development area set to accommodate over 100,000 new residents. The existing interstate rail corridor is immediately adjacent to this development and to established suburbs further north. Addition of stations and electrified narrow-gauge track for QR passenger trains will not be entirely straightforward, but will clearly be a major improvement to public transport in the area.

It is assumed that Flagstone line will be constructed as 9-car capable and run express from Salisbury into Cross River Rail. It’s unclear how far past Flagstone passenger service should run.

Some deviations from the interstate line may be worthwhile: for example, the interstate rail corridor passes 6.5km west of Beaudesert proper but any passenger service should serve the town properly.

The Gold Coast line extensions to the airport are relatively straightforward with a corridor long since planned for.

With an increased number of trains, it is critical that the existing junction just south of Salisbury be converted to a flying junction so that outbound Flagstone trains do not conflict with inbound Beenleigh and Gold Coast trains.

It also seems very, very likely that a fourth (express) track between Salisbury and Dutton Park will be required. It may yet make sense to deliver a tunnelled extension of CRR to south of Yeerongpilly (the original proposed portal), which would have the added benefit of leaving the existing third surface track clear for freight and the occasional interstate service.

The Sunshine Coast lines

The existing North Coast line, through the Sunshine Coast Hinterland, serves perhaps a quarter of the projected population of the broader Sunshine Coast in 2041. Serving Caloundra will raise that fraction to be closer to one-half, and Maroochydore closer to three-quarters.

It seems likely that maximising sector capacity and providing a reasonable frequency would result in the Hinterland line receiving a shuttle service with transfer at Beerwah. Cross-platform interchange in either morning or evening should be possible, or even both with the right layout (platforms on both sides of the Hinterland train).

Nine-car trains

A future-proofing feature of Cross River Rail is that its platforms are long enough for nine-car trains.

This is quite helpful, because trains from the Gold Coast line extension, the Caloundra branch, and the Flagstone-Beaudesert branch will all presumably use Cross River Rail. That’s three out of the four major expansions listed at the start of this document!

Of course, some other existing stations will need to be retrofitted for nine-car trains too.

Sectoral imbalance

The 2026 sector allocations quickly reveal that the suburban track pair through the city will be under-utilised; the Ferny Grove / Cleveland lines on their own will only initially need about one-third of the maximum capacity, perhaps up to one-half later. But with growth largely focused on other areas in SEQ, it may be necessary to shift other lines - or parts of them - back onto the Suburbans.

Specifically, in the south it may make sense for trains from the inner part of the Beenleigh line (e.g. from Kuraby north) to once again run via the Merivale Bridge (using the Suburbans through the city). This scenario would be triggered if even nine-car trains weren’t enough for the extended Gold Coast line and the Flagstone-Beaudesert line, and also if converting all of the Beenleigh line to nine-car length was too difficult. This would also require four tracks south from Park Road to at least the terminus of the inner line (two for the all-stops service via the bridge, two for the express services via the tunnel). Putting the flat junction at Park Road back into use is not ideal, but that should be no worse than pre-CRR and it may even be possible to grade-separate it.

In the north, if demand on the Sunshine Coast, Caboolture and Redcliffe lines exceeds what even nine-car trains can serve (or if it’s too difficult to convert Virginia-Lawnton to nine-car stations) then it may be necessary for the trains running all-stops from (say) Petrie to once again run via Bowen Hills rather than CRR. (This would presumably require a fourth track from Petrie to Northgate, to keep sectors separate.)

However, this runs into another major capacity issue: since there are only four tracks from Northgate to Bowen Hills, only two sectors can be present there. One is taken by the CRR lines, which we’re trying to offload capacity from. But the other pair is surely full too, by this point: it already has the Shorncliffe, Airport and Doomben lines, and besides, those are all flat junctions which reduce reliable capacity. We’ll really need another track pair, somewhere…

The North-West Transport Corridor, and alternatives

The NWTC reserve runs along the Trouts Rd alignment from Stafford Rd to the Gympie Arterial Rd. Some of this is quite difficult terrain, and neither end is all that close to an existing train line. Nonetheless, it has potential, both because it could bring rail service to a new part of town, and because it could be part of a more direct route from Strathpine to the city.

The most expansive vision of rail on the NWTC features a connection back to the northern tracks between Strathpine and Bald Hills, tunnelled connection to Cross River Rail in the south, and enough tracks to provide both express and local service on the corridor.

Local service would either go into CRR with the expresses, or into the Ferny Grove line. Running via the Ferny Grove line is relatively indirect, and it seems likely a 2.5km tunnel will be needed to make the connection. This also means the NWTC would need to be fully four-tracked, to accommodate the two separate sectors.

The NWTC does a number of exciting things in terms of a future northern-lines capacity crunch! If all CRR services run via the NWTC, a track pair is freed up between Northgate and Bowen Hills. However, Exhibition station is quite far east, so we’re faced with a tricky choice between (a) leaving it unserved again and (b) having a much longer tunnel back to the NWTC, almost as indirect as going via the Ferny Grove line.

That’s if we use the NWTC for express service at all.

Suppose we started tunnelling north-east of Exhibition station. If we ignored the NWTC and went due north instead, we could go via Chermside to Carseldine. It would be a long (10km) tunnel and duplicates the Northern Busway corridor, but in turn the busway provides for local service. Only Chermside would be needed as a station - after all, underground stations are very expensive.

But then again, if we’re not even going via the NWTC, we could plausibly start tunnelling at Albion station instead, with a relatively short 3km tunnel to where the Airport line branches off at Kedron Brook - in other words, sextuplicating the existing corridor.

The primary question for local service on the NWTC per se is whether the connection to the Ferny Grove line is prohibitively expensive/difficult. If it is, then local services can only go via CRR - tricky if we’re already close to filling CRR from north of Petrie.

The Western question

The fourth major expansion listed at the start of this document is the Ripley Valley extension. It’s also plausible that further development along the Rosewood line will require service increases there too, as well as demand increases around the existing parts of the Ipswich and Springfield lines. Put together, this is likely to be too much for the existing Mains track pair.

This capacity crunch has been identified at least as long ago as the late-2000s Inner City Rail Capacity Study, which recommended a new tunnel from somewhere between Indooroopilly and Milton, possibly via West End and South Brisbane in the Indooroopilly case, through the CBD, up to Newstead/Fortitude Valley and then connecting back to the existing line north of Bowen Hills. Later work, such as the Minerva Plan, suggests a “Cleve-wich line” where the tunnel continues to Cannon Hill rather than Bowen Hills, and connects with the mid-outer Cleveland line.

Some other ambitious new alignment may also be desirable, for example starting further southwest to go via UQ, going further southeast to Capalaba, or even extending north to Eagle Junction, the NWTC or other alternatives! However, demand growth is unbalanced: the Southern and Western lines will need a track pair each compared to before CRR, whereas the North only adds one. This indicates an eventual “east-west” tunnel.

If the Western lines reach capacity relatively early compared to the Southern lines, then several temporary solutions may be available. The Mains pair is particularly limited because it only has one platform per direction at Central and Roma Street, compared to two for the about-to-be-lightly-used Suburbans. With crowded platforms, trains often need to wait longer, which limits frequency.

At the expense of breaking the through-routing with the Shorncliffe, Airport and Doomben lines, those northern lines can be sent via the Suburbans (as they do pre-CRR). This would remove their passengers from the relatively-crowded Mains platforms, and in turn that may permit shorter dwell times and increased frequency. Some or all of the northern lines could then be sent over the Merivale Bridge to Park Road station, replacing the infill service (though this would only be a relatively minor clawback).

Due to the flat junction near Roma Street station, it is difficult to run western-line trains on the Suburbans through the city. But until the entirety of the Suburbans are needed for the southern lines again, it may be possible to run an all-stops service from Darra on the Suburbans while all trains from further out run express on the Mains. This would require additional works to shift the Springfield line tracks to connect with platforms 3 and 4 (shared with the Ipswich-Rosewood trains) rather than 1 and 2 at Darra.

It might also be possible to reconstruct the tunnels on either side of Central Station to swap platforms 3/4 over to the Mains from the Suburbans (also swapping 6/7 over at Roma St). This would both alleviate crowding and allow for an increased dwell time for the same frequency, or vice versa.

Central Station Shuffle: 4 tracks, 6 platforms

An alternative (and novel!) way of improving Central Station platform capacity allocation in the medium term has been described to me by Paul Kennedy. This involves (temporarily) widening platforms 3/4 and 1/2, each to the west over the tracks currently serving platforms 2 and 4. This provides “Spanish Solution” style dual access to trains on the (current) platform 3 and 5 tracks. However, for platform capacity reasons, passengers would generally be encouraged to board from the (widened) platforms 2 and 4 rather than 3 and 5. Cross-platform-interchange opportunities also arise.

Platform reallocation at Roma St is possible with a minimum of work. Future development over Roma St Station should avoid compromising the flexibility here.

Ultimately, once track amplification puts more lines back on the Suburbans, it may make sense to return Central to its current configuration. But while the bulk of the patronage is on the Mains, it makes sense that most of the platform space is too.

Conclusions

Cross River Rail will provide substantial new “core” capacity for train lines serving northern and southern SEQ.

However, not all problems are solved. There’s a need to for further upgrades on part of the existing network, a need for extensions and branches, a looming bottleneck immediately to the south of CRR, an awkward sectoral utilisation imbalance of the tracks through Central station, an eventual need for a second track pair for the western lines, and an eventual bottleneck to the north of CRR too.