Some people will tell you that rail lines down freeways are a great idea, because “the train overtaking cars is a great advertisement for public transport.”
Perth has done this, primarily because it’s been the easiest way of extending the train network. So the Clarkson/Joondalup and Mandurah lines both run down the middle of freeways.
And it’s long been proposed to build Melbourne’s Doncaster line this way, which I think makes a lot of sense.
But having seen the Perth examples up close recently just re-inforces my view that it’s only a good idea if there is no viable alternative — for a number of reasons…
Stations on freeways are very pedestrian un-friendly
As I’ve noted in the past, you are pretty much killing off any pedestrian use into the stations… and this is actually how the bulk of people reach railway stations in Melbourne at present.
You either end up having to put in lots of car-parking (which on level ground can cost tens of thousands of dollars per space, let alone the astronomical cost of multi-storey — and severely limits your patronage, as well as denying access to those who don’t/can’t drive) or you have to bring in people by feeder bus — which needs a lot of effort/cost to make it work well.
Perth has actually made the effort to put in reasonable connecting buses at some of its stations, and (from what I saw waiting around at Murdoch in the evening peak) these are pretty well used, though the adjacent car parks were busy too.
Stations in freeway reservations are also unlikely to be destinations, because shops, universities, businesses and so on — all the things that have grown around most of Melbourne’s suburban railway stations — won’t develop. These are important to make stations and trains well-used at times other than peak, and make the whole thing more viable, by catering for more than just CBD 9-5 commuters.
It’s worth noting that the Mandurah line diverges away from the Kwinana Freeway at both ends — the CBD (at a cost as it included tunnels and two underground stations) to ensure people hopping off could walk to work, and the Mandurah end, presumably because (some) land was available and cheap, so they didn’t feel constrained to just the freeway. (That said, the Mandurah line doesn’t actually reach central Mandurah; you have to catch a bus the last little bit of the way.)
Trains only overtake cars in peak hour
Let me tell you, it was great being in a train overtaking all the peak hour traffic on the Mandurah line. The trains were fast, frequent, and very popular.
Frankly, it was equally great being in a car in peak hour traffic being overtaken by trains.
But this only happens when the traffic is heavy. At all other times, including the peak-shoulder, trains don’t overtake cars because the traffic is moving faster.
Trains are at a particular disadvantage in off-peak hours, when the cars zoom along, and trains are less frequent. The result is — especially if you’re sitting at a station — the disheartening sight of waiting for 10, 20, 30 minutes while the traffic whizzes past you. That’s not a great advertisement for public transport; it’s a great advertisement for driving.
And if you’re driving and the average speed of the train is about the same (eg car at 100 kmh versus train at 130 kmh but with regular stops) you might not see any trains in the direction you’re travelling (only in the opposite direction). Again, that’s not a great advertisement for public transport.
Don’t get me wrong — a railway line down a freeway is better than no railway line. For instance in the case of Melbourne’s Doncaster line, a very obvious easy affordable project would be a “phase 1″ from Victoria Park to Bulleen, with a bus interchange at Bulleen. That would get thousands of passengers on scores of at-capacity buses out of inner-city traffic on the freeway and Hoddle Street, and encourage thousands more to get out of their cars.
But overall, down freeways is not the first choice for where you should build railways.