About 25 metres below ground, just beyond the Woolworths national headquarters at Norwest, Elizabeth is boring away.

As of Tuesday afternoon, she had travelled just over a kilometre, grinding her way forward in bursts of 1.7 metres.

For traditional reasons, tunnelling machines tend to be named after women. And Elizabeth, the first machine to start digging on the north-west rail link project, is very much the apple of the Baird government's eye: evidence, it will claim, of rare progress in the delivery of major transport projects.

"If you think that we are basically targeting opening in mid-2019, we have come a long way," says project director Rodd Staples on a site tour of the north-west rail link tunnels, the largest rail tunnels in the country's history.

"More than one kilometre has been done," says Staples. "It is a big achievement."

The tunnel carved by Elizabeth is one of two that will run from Bella Vista to Cherrybrook. Another two will run from Cherrybrook to Epping, where they will emerge near the adjacent Epping to Chatswood line.

Each machine – as well as Elizabeth, Florence and Isabelle are also underground, and a fourth is to come – hosts a crew of about 15 working at any one time, over three shifts at all hours of day and night.

The work is close and cramped. But for Tim Burns, the project manager for contractor Thiess John Holland Dragados, the processes used are a welcome change after having worked on the Epping to Chatswood tunnels.

"There's a massive improvement on the north-west rail link," says Burns.

"This is a segmentally lined tunnel," he says. He is referring to method by which the tunnel machine carves its way forward at the same time as it locks 1.7 metre wide concrete segments to the walls of the tunnel.

In contrast, when the Epping to Chatswood tunnels were built, the concrete walls were installed after the tunnel was dug.

"This way we get better quality in only one go," he says.

When the six segments are bolted in place, they form one "ring". After a ring is formed, the machine uses grippers that extend to the tunnel wall, which drive the machine forward by the length of the ring. The machines average about 30-35 metres a day.

In a project of this scope, the cost will be somewhere around $8.5 billion. There are plenty of grandiose statistics to quote.

Back at Bella Vista, a concrete batching plant will produce about 100,000 concrete segments to form the rings and the walls of the rail tunnels. The plant has already amassed a stockpile of about 20,000 segments.

And when the four machines are tunnelling, they will each send about 3300 tonnes of spoil a day out of tunnels on conveyor belts.

You might see evidence of spoil on the roads in the next few years, as 100 trucks a day per tunnel cart it to other parts of Sydney.