One of the things people have been wondering is whether the Suburban Rail Loop will be an integral part of the existing suburban Metro network, or a standalone line.

Melbourne’s existing rail network has its origins in the 1854 line from Port Melbourne to Flinders Street (since converted to trams), but also particularly in the electrification of the 1910s and 1920s, to the standards of the time, including 1500 volt DC power.

While the SRL will have many interchanges with the existing network, there’s no particular reason it has to use the same technology.

The State Government announced on Sunday that SRL will indeed be different.

Similar to the NSW decision to make their new Metro line independent of the double-deck suburban lines, the SRL will be completely separate from the suburban network.

From the press release:

It will be built as a separate rail line, meaning it can use state-of-the-art systems from around the world without having to retrofit technology into the existing network – saving time and money. Passengers will be able to easily transfer across both networks, with the same ticketing system servicing both and up to 12 new stations connecting the existing rail system with the new standalone line.

SRL as a completely separate rail line brings a number of advantages.

Smaller, shorter trains running to higher frequencies can be used – better meeting the non-tidal capacity requirements of a line that doesn’t serve the CBD, while providing real Turn Up And Go services that make interchange from other lines and modes quick and easy.

The key would be to provide infrastructure that makes it possible to easily scale-up capacity as demand grows.

Nobody wants a repeat of the tram 96 situation, where the conversion from high capacity heavy rail to medium capacity light rail, combined with population growth, has seen heavy crowding, with demand swamping the trams.

A segregated fleet means platform screen doors can be used at every station, improving safety.

(Platform screen doors are flagged for the metro tunnel as well, though theoretically could also be retro-fitted at most stations between Sunbury and Cranbourne/Pakenham – with the possible exception of platforms shared with V/Line. And full platform shelter might be required to make it work.)

Smaller trains may mean a smaller loading gauge, helping to reduce tunnelling costs… or indeed the potential to use standard gauge tracks.

Modern AC power can reduce costs as well – as I understand it, fewer substations are needed compared to the 1500 volt DC power used by suburban trains.

If the line is completely grade separated and independent, it also means driverless trains are possible. Again, the new Sydney Metro line uses these, as do an increasing number of urban train services around the world, including parts of the Singapore MTR, Vancouver’s Skytrain, and London’s DLR.

At this stage the Government seems reluctant to commit to full automation.

Of course there are some disadvantages from using different technology.

Fleets could not be exchanged with other existing Melbourne lines, limiting flexibility. The deployment of new vehicles, and the cascading of others around the network is common on some networks, including Melbourne’s trams.

These types of factors become less important as the network gets bigger. Overall it seems to make sense the way they’re going. The pros outweigh the cons.

I’m more concerned about them adding some intermediate stations (or at least future provision for them) to the longer stretches of the route, to help ensure plenty of people have access to the line.

Given the apparent wish to seek private investment, it would make sense to have stations at some locations which are not already developed to a high density.

There is also a strong argument for including Doncaster in the first section (currently flagged as Cheltenham to Box Hill) given Doncaster is one of Melbourne’s biggest centres with no rail connection.

Provision for a future connection from Cheltenham to the Sandringham line would also make sense.

And there are still questions about the Airport section of the line, connecting through to Sunshine. I suspect Sunday’s announcement means SRL trains will share the alignment with City to Airport trains, but use separate tracks – but given that’s SRL stage 2 or 3, that decision is a long way off.

It’s good to see the Suburban Rail Loop progressing. It looks like we can expect to see construction begin by 2022 – just in time for the next state election.

As it comes into service, it will revolutionise cross-suburban travel by providing fast frequent connections around the middle-distance suburbs – opening up opportunities in jobs and education.

It does mean it becomes even more important to reform and upgrade bus routes and service frequencies to help more people easily reach the rail network.

And building the SRL is not an excuse for not providing 7-day all-day frequent services on the suburban trains – as well as progressing other major rail infrastructure such as Metro 2.

Our growing city needs it all to help more people get around without adding to the traffic.

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