It’s important to have a long-term plan. PTV has one for rail which is published here:

PTV Network Development Plan – Metropolitan Rail

— I’ve blogged about this plan when it was released.

Upgrades such as the Melbourne Metro Rail Tunnel and the new fleet of trains tie into this plan, and complement each other: the tunnel and its stations will be designed for the longer trains that the new fleet will deliver.

Here’s one snippet of information I had been asked about, and was wondering about, but was able to confirm with the project team recently: The metro rail tunnel will NOT be built to cater for double deck trains.

Obviously long tunnels are expensive. A decision has to be made about their size, and the smaller the better. In this case, they are not willing to invest the extra cost for provision for possible future double deck trains.

We’ve tried double deck trains before

The City Loop does cater for them. In the 70s when it was built, there were no definite plans for double deck trains (Hitachi trains were coming into service at the time), but they were considering it for the future.

A trial of a double deck train (the Federally funded “4D” — Double Deck Development and Demonstration Train) was done in the 1990s. Here it is in operation at Parliament:

It was modelled and based on Sydney’s double deck trains, but seemed to have continual reliability problems. It mainly ran on the Belgrave and Lilydale lines, but some other lines had the requisite bridge clearances. No doubt if a further rollout was planned, more bridges would have been modified.

Reliability aside, the authorities decided that such trains were not the way of the future. No more were built. The train was eventually sold to RailCorp NSW for spare parts, and scrapped in 2006.

The policy of staying single-deck is, when you look around, reasonably obvious: the recently rebuilt Springvale station doesn’t have a lot of space to spare above our current single deck trains.

(By the way, as I understand it, double stacked containers are not compatible with overhead wiring, so we won’t see them on our suburban tracks.)

There have been other Melbourne trials of new public transport vehicles. Marcus Wong has a great blog post about various tram types tested and rejected here. At least one test was successful: the initial B-class trams (2001 and 2002) in 1984-5 was followed by over 100 more brought into service in the late 80s and early 90s.

Is single deck or double deck better?

Arguments about this will rage forever I suspect, but there are pros and cons to each.

For a higher carrying capacity, single deck trains need to be longer, providing more doors, and theoretically faster loading and unloading. Faster loading means you can push more trains down the line, and helps counter some or all the capacity benefits of double deck.

Longer trains have an obvious cost: longer platforms and it may have other impacts such as on signalling and stabling. This is where Melbourne is going — the new fleet will start at 7 cars and extend to 9 or 10.

Double deck trains have higher capacity for the length — about 50% more. But they are obviously higher, meaning some existing tunnels and bridges need modification (which may or may not be practical) and extra cost when building new track, especially tunnels.

The power-to-weight ratio of the train could be an issue. Double deck trains obviously concentrate a lot more weight per carriage, while single deck trains that spread the load out over more carriages and wheel sets may assist good acceleration.

Some people will cite security issues, as the decks mean it’s not possible to look along the length of the train. Some also cite risks with level crossings, as the lower deck is vulnerable to a motor vehicle impact, though I’m not sure if that risk has been quantified.

Most cities have stuck with single deck for their high-capacity, short trip urban and metro networks, though the Paris RER is a prominent example of double deck high-capacity suburban operation, and they’ve designed double deck carriages with a third doorway, presumably at the cost of capacity. But I’m not sure any new lines or networks are being designed for double deck operation.

A number of European countries including Belgium, the Netherlands and Switzerland use them, but primarily for longer distances, where dwell times are less important.

NSW is moving to single deck for their new metro line. Meanwhile the UK is considering double deck for its commuter lines (eg NOT the Tube, which has tunnels that are very space-constrained).

No double deck for you!

The metro tunnel decision means for better or worse, Melbourne is sticking with single deck.

I don’t have a major problem with this.

It’d be nice to see the findings from the 90s trial out in public, but as long as the reasons for the decision have been thought through, carefully considered, and are understood, the focus can be on optimising the network for single deck operation.

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