Reality aside, what are the options for a Brisbane inner-city metro? Taking into account Brisbane's population, the most appropriate type of metro system would be a driverless mini-metro systems such as Copenhagen's Metro (Andsaldo-Breda). Mini-metros use short trains (and thus platforms) at approx. 30-80m in length with a small to medium profile train width of between 2 to 2.8m (which can reduce tunnel diameter) to considerably reduce construction costs. Trains can run at very high frequency to make up for the short train length, with capacities in the approx. 10,000 to 30,000 passengers per hour range. It should be noted that manufacturers often quote theoretical maximum capacities rather than actual operating capacity, however mini-metros typically operate trains between 90 second and 3 minute headways. Driverless trains allow for lower operating costs, and higher operating flexibility. Driverless technology is now mature and has an excellent safety record.
There are many different track and propulsion technologies that can be used by mini-metro systems. BrizCommuter runs through the different technologies:
Rubber-tyre - rubber-tyred trains are commonly found on French influenced metros (Paris, Mexico City, Santiago, Montreal, Lausanne), and many Automated People Mover (APM) / Automated Guided Transit (AGT) systems, such as Siemens VAL (Lille, Turin Metros), Bombardier Innovia APM (Heathrow T5), and Mitsubishi Crystal Mover (Singapore Airport). Whilst for heavy metro systems new rubber-tyred lines are dying out, the technology is useful for mini-metro systems. The extra grip allows for steep gradients (up to 12%), and sharp corners (30-50m) which can help reduce construction costs due to more alignment possibilities. Multiple manufacturers offer rubber-tyred systems, however some APM/AGT designs can potentially lock the buyer into using a single manufacturer.
Linear Induction Motor - linear induction motors are commonly found on the many Bombardier ART systems (such as Vancouver's SkyTrain), and many Japanese Metro systems (such as Tokyo's Oedo Line) from multiple manufacturers. The linear motors allow for less space under the train floor, allowing for a smaller profile train which can decrease station and tunnel construction costs. Linear induction motors also can allow for steep gradients (up to 8%), and sharp corners (50-100m) which again can help reduce construction costs. Choosing a linear induction motor system could potentially lock the buyer into using a single manufacturer. Interestingly, Bombardier now offer a rotary motor version of their ART system where the train floor is only marginally higher than the linear motor version.
Conventional - steel wheel on steel rail, and rotary motors are the most common metro system track and propulsion technology. Virtually all manufacturers offer metro systems using this technology, which allows for simpler technology (i.e. cheaper), more competition, and less likelihood of relying on a single manufacturer for system upgrades. The downside of that the alignments of the metro system will be restricted to shallow gradients (3-4%), and less sharp curves (100-400m) which could result in more expensive constructions costs for more demanding alignments.
One interesting thing to note for Brisbane's mythical inner-city metro system is where the depot would be located. The current route only really has space for a depot on current semi-abandoned railway land near the Hamilton Northshore development. If this land is not safeguarded from development, then the result could be having to extend the line further to access and suitable for a depot (more $$$), or build and underground depot (more $$$). Likewise other future developments along the route could make for more difficult and expensive construction. London's CrossRail Line 1 and 2 routes have been safeguarded for decades under various guises, lets hope that same happens for Brisbane's inner-city metro, otherwise we could be waiting even longer!
Copenhagen's Driverless Metro