On Monday Marcus Wong found a media release from the Melbourne Metro Rail Authority (MMRA) that announced the construction of a third platform at West Footscray Station on the Sunbury line as part of the Metro Rail Tunnel project.

The Metro Rail Tunnel is the proposed construction of a cross-city rail line connecting the Sunbury line to the Pakenham/Cranbourne line via a tunnel through the centre of Melbourne. It is needed to address capacity constraints that are forecast to cripple the City Loop.

On the face of it such a side project looks odd. Why terminate trains so close the city, surely there is not the passenger demand for a whole train just from West Footscray to Melbourne? But looking deeper it appears the MMRA is looking for a way to terminate the many trains from the Pakenham/Cranbourne line, not all of which are needed yet on the Sunbury line. West Footscray is the first location heading west from the city with enough room to terminate these extra trains without delaying the mainline or acquiring property.

The frequency for the Metro Tunnel would still be in planning, but we do know that the line will be fitted with high capacity, in-cab signalling which elsewhere in the world allows 30 trains per hour, or one train every two minutes. As seen from Public Transport Victoria’s Network Development Plan, it is intended to run lines though the tunnel that are yet to be constructed as well as the existing Sunbury, Pakenham and Cranbourne lines. From the west, lines that would use the tunnel are Melton, Sunbury and the Airport. From the east; Rowville, Pakenham and Cranbourne. This effectively creates three end-to-end lines.

So, 30 trains per hour divided by three lines is 10 trains per hour per line. 60 minutes divided by 10 trains gives a frequency of one train every six minutes per line. It is unlikely that there will need to be trains every six minutes to the end of all these lines so it would also be expected for some of these trains to terminate short at Watergardens and Westall.

Before these new lines are running, however, there will be more trains coming from the Pakenham/Cranbourne line than would be needed on the Sunbury line and this brings us back to the third platform at West Footscray and the problem it solves for the MMRA.