The agency building the WestConnex motorway wants to move the key rail line linking Sydney's west to Port Botany under plans to build separate motorway connections to Sydney Airport's domestic and international terminals.
The Sydney Motorway Corporation is yet to finalise a plan to link WestConnex to the airport, one of the original justifications for constructing what has become Australia's largest motorway project.
But under the latest plans for the "Sydney gateway", a motorway of two lanes each way would split much closer to St Peters in Sydney's inner west than had been previously envisaged. One arm of the new roadway would connect to the international terminal and the other to the domestic terminals known as T2 and T3.
The tentative plans would require moving a rail freight line near the northern boundary of the airport about 500 metres north. The single rail line connects Port Botany to Sydney's west.
Sydney Motorway Corporation chief executive Dennis Cliche said possible corridors for the roadway from St Peters to the airport would involve navigating around a significant number of properties.
The new motorway connection could result in significant changes to Qantas Drive, which is at the northern edge of Sydney Airport and connects to Airport Drive and Joyce Drive.
Shifting the rail link would also require commercial negotiations with organisations such as Sydney Airport, transport companies Asciano and Qube, and NSW Ports.
"The rail link is right in the middle of this zone," he said of the plans to build the motorway links to the airport terminals from the interchange at St Peters. "By moving the rail, we have got more opportunity.
"It is part of the airport's future plans as well. We have done the concept and taken it to the point of costing. There is still a large amount of work to go."
The latest designs highlight the way in which the WestConnex project continues to expand. The motorway has morphed from a $10 billion roadway in 2010 into a near $16.8 billion project.
But that cost does not include some major future elements envisaged for the project. These include another road crossing of Sydney Harbour and a motorway to the Sutherland Shire.
Around Botany, the state government has said it wants a duplicated rail freight line from the port to Sydney's west where major logistics terminals are to be built.
Mr Cliche said the cost of the "Sydney gateway" had risen because of the plan to split the roadway closer to St Peters, and provide roadways to both terminals.
Infrastructure NSW is working on the details of the "enhanced version" of the Sydney gateway.
A spokeswoman declined to provide details but said it was working to ensure there was an "appropriate connection" from WestConnex to the airport and port.
Under the plans for WestConnex, the major interchange at St Peters will link the Sydney gateway to the new M5 East, and tunnels connecting the M4 to the M5 motorways.
The original design for stage three of WestConnex, including a motorway link to the airport and Port Botany, was done before the government's plans to sell state electricity assets, Mr Cliche said.
While officially part of stage two, the Sydney gateway is not expected to be opened to traffic until 2023 – the same timeframe for stage three.
The state government also plans to upgrade roads around Sydney Airport to ease congestion, including General Holmes Drive and Botany Road.
Mr Cliche described as a "vote of confidence" in WestConnex the raising of $1.5 billion of private sector debt late last month from Commonwealth Bank, Westpac, National Australia Bank and a French bank.
"That was an acid test for our project. If we couldn't convert that high-level interest into hard loans we would have been in trouble. But we did and that is why it is quite significant," he said.
"We have the ability to raise debt, sell equity or hold [in the longer term]. There are many options."
