“Skyrail” blog coming in a day or two, but first another related issue to cover: How many tracks is best?
Single track can work for very infrequent rail services, but in a suburban setting, with frequent services, causes problems.
Witness the Altona Loop — the single track (with passing loops) severely limits the number of trains that move through — a maximum of three trains per hour in each direction. Even during normal operations, trains have to wait for each other at passing loops (the photo above is at Westona).
Any little delay can quickly escalate, so Metro often have trains bypass this section altogether, leaving 44+ minute gaps in the middle of peak hour. The latest Track Record quarterly report says this happened 393 times in the year to September 2015.
Single track really has no place on a modern suburban train network. Puffing Billy? Sure. But not Metro. Yet it persists on the Altona Loop, and lines to Upfield, Hurstbridge, Lilydale, Belgrave and Cranbourne.
Double track is obviously the default, allowing trains in both directions without causing delays. Express running (including for long distance trains) can be tricky to manage — the Dandenong line manages a bit of this, but at peak times the V/Line expresses are little faster than the stopping trains.
Three tracks was fashionable in Melbourne up until the 1980s, with prominent examples on the Ringwood and Frankston lines. Expresses can overtake slower trains in one direction only.
The catch is that since the 1990s, the amount of inner-city stabling has been reduced markedly, so all those trains need somewhere to go between peak hour runs. This is problematic with three tracks — in the morning the single outbound track gets congested; this can result in delays and clogged level crossings, and may be problematic when aiming to connect outer suburban centres like Dandenong and Ringwood with express trains (in both directions) from the inner city.
Four tracks is now what they’re moving to when building for extensive express running. Separate track pairs can isolate different lines and/or keep stopping and express trains apart.
City to Footscray expanded from two tracks to four in the 1970s. With Regional Rail Link, it expanded again to six.
So when you look at lines like the Dandenong line, remember: it’s two tracks now (and the “Skyrail” will initially also be two tracks). But planning and provision for future expansion will be for four tracks, not three.