Crosstown rail probably should be built closer to the city centre, then further crosstown rail lines progressively further out.
Melbourne's system carries 237 million riders per year, Paris RER 1.1 billion, 4-5 times more riders, but Paris urban area is 3 times bigger too. All of the commuter rail in NYC area is 273 million per year serving 3-4 times bigger population.
237 milllion for suburban rail, 204 million for tram, but only 118 million for bus. I can't help but wonder if the overall ridership would be much better if there wasn't so much focus on suburban rail.
Paris has RER but it also has Metro. NYC has Long Island Rail Road and Metro-North Railroad, but it also has the Subway. Melbourne seems to lack a comprehensive and integrated transit network, with a true metro system for the city centre and a highly-developed suburban bus network to feed into the rail system. A 50km-long suburban subway line doesn't seem like the solution.
Code:
Urban Area Commuter Metro Tram Bus Total Per Capita
Melbourne 237 0 204 118 558 122
New York 273 2858 21 974 4126 225
Toronto 54 303 96 602 1055 194
Vancouver 2 137 0 240 379 167
In 1950, transit in Melbourne had 449 boardings per capita, now it's only 1/4 of that. Maybe so much investment in the suburbs is part of the reason for that in the first place.