After a year when Sydney’s existing double-decker rail network was crippled by an industrial dispute between the state government and rail unions, it is crunch time for the $18.5 billion City and Southwest project as the opening date for the main section from Chatswood to Sydenham next year fast approaches.

Buffeted by the pandemic and the industrial dispute, the City and Southwest project is $6 billion over budget, while a section of the line from Sydenham to Bankstown will open in 2025 – at least a year late.

City and Southwest project director Hugh Lawson says it is a “complex mega project”, underscored by the fact that building just one of the six new stations is an enormous task in itself.

“We’re trying to do that across a whole line and bring it all together in a really co-ordinated way,” he says. “Then put on top of that COVID, construction pauses, industrial action, weather and everything else and our challenge is to constantly be adapting ... and making sure we keep the project moving.”

The next critical phase involves completing rail systems to enable power to be switched on, clearing the way for testing of the entire train line. All of that is running in parallel with work to finish fitting out of stations. “It all has to come together at the end – ready for day one of opening,” Lawson says. As well as six new stations, the project involves building new underground platforms or upgrading those at 12 existing stations.

Chiselled out of sandstone, it is the largest rail line to be constructed under central Sydney since the City Circle underground railway was completed in the 1950s. Built in stages over three decades, the City Circle was devised by chief engineer John Bradfield, modelled on New York’s subway.

More than half a century later, the genesis for a fully automated metro rail line under the harbour and CBD lies in a 2012 blueprint for Sydney’s railways, developed in the year after the Coalition swept to power in the state election. The report, Sydney’s Rail Future, was a long-term plan to boost the rail network’s capacity, making clear the need for a rail spine under the CBD to ease pressure on the City Circle. Despite the need for extra capacity, it was a challenging period to launch the blueprint because of deep public scepticism that a rail line under the central city would ever be built.

The state’s then transport chief, Les Wielinga, was pivotal in getting it off the ground, realising years earlier the need for a second rail crossing of the harbour when he was head of the NSW roads authority. “I knew we couldn’t solve all of Sydney’s problems with just roads,” he recalls.

However, Wielinga admits it was “a very close thing” that the City and Southwest project became a reality due to opposition within parts of the new Coalition government at the time, and after the Keneally Labor government abandoned plans in 2010 for a seven-kilometre underground rail line between Central Station and Rozelle in the inner west. “[The heads of Infrastructure NSW] Nick Greiner and Paul Broad were against it because they wanted to build large road projects. We had to fight Treasury, and we had to fight a number of government ministers who weren’t keen to spend that much money on a public transport system,” he says.

A decade on, the former top public servant is adamant that the City and Southwest rail line – when linked with the 23-kilometre Northwest Metro which opened in 2019 – will be the most transformative piece of transport infrastructure since the Harbour Bridge opened 90 years ago. “It will provide the backbone that Sydney has needed for a long time,” he says. “It is going to advantage particularly south-western Sydney. The public transport system should help people from the south-west get to employment in the CBD.”