Pressure is mounting on the Morrison government to commit money to help pay for the expected $20 billion-plus cost of a new metro train line from central Sydney to Parramatta.

While federal Labor had promised $3 billion for Sydney Metro West prior to the election, the Coalition has not said whether it will commit any funding to the ambitious rail project.

But Sydney Business Chamber's western Sydney director, David Borger, said the federal government needed to stump up for Metro West because the project was crucial to relieving congestion on roads and existing rail lines such as the T1 Western.

Passengers on a Metro Northwest driverless train this week.CREDITETER RAE

"It is the sort of project that we can't afford to kick the can down the road on. The strongest housing growth in Sydney is along the western corridor," he said.

"It is fine for Commonwealth leaders to talk about congestion [relief] in terms of roundabouts, but if we really want to bust congestion we need metro rail."

Mr Borger said the Berejiklian government's $6.4 billion commitment over four years to the Metro West line was a solid first step but Commonwealth support was needed to close the funding gap.

The latest funding push comes as figures show Sydney's first metro line is proving popular among commuters. More than 72,000 people travelled on the line's driverless trains on each weekday on average last week, making it almost as busy as the Eastern Suburbs rail line.

The Berejiklian government has promised to start construction on Metro West next year, and complete the line by 2028.

Transport Minster Andrew Constance declined to comment on whether he believed the federal government should commit funding to Metro West.

However, he has previously compared the rail project to the Harbour Bridge in the impact it could have on the city, stressing its importance as the T1 Western Line approaches capacity.

A commuter snaps a selfie outside Hills Showground station on the new Metro Northwest line. CREDITETER RAE

Federal Cities and Urban Infrastructure Minister Alan Tudge would not say whether federal funding would be forthcoming, instead citing money set aside for other projects in western Sydney.