More than 42 m below the Melbourne CBD, a new metro tunnel is set to transform the city’s rail network.
By Joe Ennis, Joseph Harding and Lachlan Haycock
With twin nine-kilometre tunnels, five deep-level stations, advanced signalling and a high-capacity communications-based train control (CBTC) system, this $15 billion piece of infrastructure is set to reshape how commuters move through the heart of the city.
Tunnelling and station construction
Four tunnel boring machines excavated simultaneously from both western (Arden) and eastern (Anzac) portals. The machines operated at pressures up to three bar to maintain face stability through complex Coode Island Silt and Melbourne mudstone strata.
Each tunnel lining ring consists of six precast concrete segments plus a key, manufactured locally.
A box cut solution was possible at three of the stations, namely Arden, Parkville and Anzac. Located outside the CBD and therefore less likely to disrupt or be disrupted by surrounding architecture, space for these stations was created by digging directly down into the ground: in essence creating a box-shaped rectangle in the ground.
The two CBD stations, State Library and Town Hall, required a different strategy.
“There was a shallow tunnel option along Swanston Street, but that would have closed the street for at least five years,” Deputy Director of Delivery Jim Heron previously told create. “We would have had to dig up Swanston Street, disrupting traffic and tram flow.
“There would be other issues such as undermining existing structures and moving utilities off the street. Utilities are seen as a risk to a project because of the cost of and time for removal.”
Owing to the difficulties associated with an open cut and to keep Swanston Street relatively intact across the project’s lifetime, the decision was made to change tactics on the two CBD stations.
This led to its own technical challenges.
“Logistically feeding the two CBD stations is challenging because everything goes in and comes out through the same shafts,” Heron said. “At the box stations we could layer in columns and slabs from above, but in the CBD we had to do a lot more work overhead to support the ground above.”
Signalling innovation
The Metro Tunnel introduces Australia’s first network‑wide deployment of a CBTC system on a broad‑gauge railway. The Siemens HCS system uses continuous bidirectional radio communication between trains and control centres, replacing fixed‑block signalling with moving‑block operations.
Key features of the signalling infrastructure include:
Real‑time train positioning allows for safe separation at distances as short as 90 seconds under design conditions.
Automatic train protection (ATP) and automatic train operation (ATO) enable smoother speed regulation and precision stopping.
Integrated control from the new Sunshine Signal Control Centre oversees traffic management, energy consumption and system diagnostics.
Fail‑safe redundancy is achieved through dual radio channels and a resilient fibre‑optic backbone.
This system allows a higher line capacity of up to 60 per cent, optimising dwell times and throughput without expanding track infrastructure. HCS also allows dynamic scheduling and adaptive speed profiles, reducing energy use and mechanical wear.
Take a look inside the stations during construction using the image carousels below.
Platform screen doors
The Metro Tunnel introduces platform screen doors across all underground stations, marking their first use in Melbourne. Each platform incorporates full‑height glass barriers with synchronised automatic doors.
These offer a variety of benefits:
The doors prevent track intrusions, accidental falls and unauthorised access, significantly reducing service disruptions.
Environmental control creates a sealed platform environment, enabling efficient air‑conditioning and smoke extraction systems in deep tunnels.
Pressure mitigation reduces air pressure fluctuations caused by piston effects from approaching trains, improving passenger comfort and tunnel ventilation efficiency.
Operational precision requires exact stopping accuracy, achieved via ATO and CBTC integration, enabling high throughput and consistent dwell times.
The project also includes new power substations, tunnel ventilation plants, emergency egress cross‑passages every 230 m, and a CBTC fibre network interconnecting trains, platform screen doors (PSDs) and control systems.
The high capacity metro trains (HCMTs) – built by Evolution Rail (Downer/CRRC/Plenary) – feature open gangways, wider doors, regenerative braking and full CBTC compatibility. The trains’ braking curves and door synchronisation systems are tuned for precise interaction with PSDs and ATO functions.
Capacity and performance outcomes
Headway: Target design ≤ 120 seconds
Train capacity: Approximately 1380 passengers per seven‑car set; scalable to 10‑car (~2,000 passengers)
Line capacity: Up to 24 trains per hour in peak operation
Energy efficiency: Regenerative braking and smart ventilation expected to cut traction power consumption by 10-15 per cent
Get an inside look at the Melbourne Central Station upgrade with a site visit organised by Engineers Australia on 28 November.
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