The first section of the Albion Park Rail bypass is now open to traffic - but only for a short while.
From Sunday, traffic was moved off the existing Yallah Road to the new section of that road just to the south, built as part of the bypass.
The shift is to allow for utility relocation work to take place on the existing Yallah Road - and will be in place for eight weeks.
After that time, traffic will be moved off the new stretch to allow for construction of the bridge over the road to continue.
NSW Premier Gladys Berejiklian stopped in at this stretch of road on Tuesday during a visit to the Illawarra and South Coast.
The Premier said more than 500,000 hours of work have gone into the bypass so far, with 25 per cent of the job completed ahead of the planned 2022 completion date.
"I'm really pleased to see that we are on budget and on time," Ms Berejiklian said.
"I always say to my team as the Premier, if we can do things ahead of schedule and under budget that's even better. The progress I've witnessed today has exceeded my expectations."
The Premier said the weather had helped with the pace of construction but wouldn't be drawn on whether it is ahead of schedule.
"We've started six out of the 13 bridges, so the project's really coming to life - and I'm always optimistic about time frames. It's certainly within the time frames we announced. And if we can do things even more quickly we will."
Kiama MP Gareth Ward said the bypass was a "region-changing project".
"It's something that people talked about for 40-50 years and so many people said 'I'll never be alive to see it'," Mr Ward said.
Mr Ward added that two of the 13 bridges, two would be constructed over Yallah Road.
"These twin 28-metre long bridges, which pass over what will be the new Yallah Road, are on track for delivery in early 2020," Mr Ward said.
"With these bridges, Yallah Road becomes an underpass which will facilitate important local connectivity between Yallah and Haywards Bay as populations in those areas grow."
The road surface along the entire length of the bypass has been raised above ground level - by more than five metres in the area around Yallah Road.
The clean fill used to do that has come from excavation elsewhere on the work site, but around one million cubic metres has to be imported.
Some of that is from the tunneling in Sydney for various road projects, which is then trucked down to the Albion Park Rail site during the night.