An artist's impression of the sky rail, commissioned by Murrumbeena resident Edward Meysztowicz. But some time beyond 2018, a future Victorian government will face a painful choice of either building a new rail viaduct down the middle of the two raised viaducts the government is to begin building this year, or potentially acquiring dozens of properties between Carnegie and Hughesdale. The Level Crossing Removal Authority, which is in charge of the project, insists the sky rail design unveiled last month includes provision for the future construction of a third and fourth track. But it has refused to reveal basic details of where those tracks will go. "The third and fourth track is not part of the level crossing removal project," authority chief executive Kevin Devlin said.

"The alignment of these tracks will be determined in the future, as part of a separate project." However, The Age has learned of planning details for the extra tracks. Public Transport Victoria estimates the extra tracks will be needed from 2030, based on forecast passenger demand for Melbourne's busiest and most overcrowded rail line. About 37,000 passengers are expected to travel on the Cranbourne-Pakenham line in the two-hour morning peak by 2030, more than double current levels and thousands more than on any other line in Melbourne. In planning for this huge growth, PTV and the Level Crossing Removal Authority struck a confidential agreement last year on what can be built now on land where the third and fourth tracks will eventually go.

Under this agreement, sky rail infrastructure that could be demolished or built over for the extra track pair includes shared walking and cycling paths, station platforms, station car parks, lifts, ramps, buildings and minor utility services. The Level Crossing Removal Authority agreed to this, on the condition that it did not add to the $1.6 billion cost of the current project. The rail corridor is just 20 metres wide at its narrowest point between Grange Road in Carnegie and Poath Road in Murrumbeena, making it difficult to build four tracks without acquiring residential property along the line. Edward Meysztowicz​ and his family own a house in Murrumbeena that backs onto the northern side of the line. In meetings with the Level Crossing Removal Authority, Mr Meysztowicz obtained the dimensions of the planned sky rail structure, and its proximity to his home.

The authority confirmed the viaduct will be 10.6 metres above ground level and 4.3 metres away from his back fence where it runs behind his property. He used those dimensions to commission an illustration of the sky rail from his own backyard. Mr Meysztowicz runs a business in industrial Dandenong South and insists he supports new infrastructure, even on the rail line behind his home. But he argues the government is thrusting a cheaper, inferior option on the public, and should spend what it takes to build all four tracks below ground level now. "Do it once but do it properly," he said.

Only when the third and fourth tracks are built will the true scale of sky rail be revealed, he argued - a rail viaduct that will dominate and transform the suburban environment far beyond what is depicted in the authority's promotional material. Mr Meysztowicz also commissioned speculative images of his neighbourhood with a third and fourth track. "The sheer bulk of sky rail in the landscape demands cloaking with multi-storey development," Mr Meysztowicz said. "This is inter-generational infrastructure our children will be grappling with." Jeremy Reynolds, an urban planner who played important roles in Melbourne's development from the 1970s until his retirement in 2014, agrees that the Andrews government has failed to be up-front with the community about the fact that sky rail is "just part one" of long-term plans for the Cranbourne-Pakenham rail line.

"Given the scale of patronage growth, surely the government should be openly planning for four tracks between Caulfield and Dandenong now," Mr Reynolds said. "The Level Crossing Removal Authority does say that the current two track proposal makes allowance for additional tracks to be added in the future and that the future project will be subject to a separate planning, design and consultation process. "But this has not been made clear to local residents as they gawp at slick videos, paw over designs for linear parks and worry about noise and light consequences of just two elevated railway tracks."