Apologies for any misunderstanding, I wasn't sure if you were suggesting two tracks on each level, but your figures do indicate that 15 metres would fit four tracks comfortably. The remaining question is if it would actually fit. I seem to recall that the reservation is quite narrow around Carnegie and Murrumbeena, and on the Up side of the road overpass at Oakleigh, but am happy to be corrected on that. Come to think of it, what would happen at Oakleigh, and at any similar road overpasses? And how would you envisage the interface at Caulfield?
I currently have 42 outside and 27 inside. No doubt we will hear of speed restrictions and/or buckled rails, and of course these will all be the operators' fault.
No problems, you correctly asked for a clarification.
The rail reserve between the route 17 level crossing and Murrembeena appears to be 20 metres wide, its VERY likely the reserve is 1 chain (66ft or near 20 metres) wide, likely still enough room for a 4 elevated tracks (Note 1). Interestingly the track reserve out to Clifton Hill is only 14-15 metres wide, mind you Collingwood (In 1880 the whole area was known by that name) was all there prior to the railway, so they had to basicly "buldoze" there way through the suburb to create the formation so they probably took as little land as they could.
For the existing overpass's the obvious answer would be to keep the track as is, all suburban rolling stock an easily handle a 1 in 30 grade so the ramps to any elevated track need only to be around 240 metres long.
Note 1: This is what engineering counsulatances are for (to answer difficult design issues).
PS: time 1710 still 42c, and the change has only just entered western Victoria, will not reach here (NE Vic) till WELL after midnight, what a pain..............sigh!