The O’Farrell government intends to build the with 15 kilometres of double small-diameter tunnels (around 6m). These will fit only single-deck metro-style rolling stock. Compared to the standard-sized tunnels of the Epping-Chatswood line, which have walkways 850mm wide, the NWRL’s planned narrow tunnel size allows only very narrow and height-constrained escape walkways. They will be too narrow for wheelchairs or stretchers.
It’s also expected that trains will have no driver or guard. It’s also been reported that the power source will be 25,000 volt AC rather than the standard 1500 volt DC used by the rest of the Sydney system. The small tunnel diameter also means that overhead power wires will be very close to the roof of the train, bringing the risk of arcing between the wiring and the carriages.