Thousands of people will be worse off when the Sydenham-to-Bankstown heavy rail line line is converted to a Metro service, a NSW parliamentary inquiry has been told.

Key points: Nine stations west of Bankstown will lose all direct rail connections to the city

Nine stations west of Bankstown will lose all direct rail connections to the city Almost 20,000 commuters will be forced to change trains twice to reach stops including Town Hall and Redfern

Almost 20,000 commuters will be forced to change trains twice to reach stops including Town Hall and Redfern Sydney University says its students and staff will be disadvantaged by the plan

The inquiry into Sydney Metro Southwest yesterday probed how the multi-billion dollar project will blow-out some travel times after direct services are cut.

Around 20,000 commuters will lose their express trains to the CBD in the next three years when work on the new Metro line commences.

The stations facing cuts as part of the multi-billion-dollar blueprint to overhaul Sydney's rail network are Berala, Regents Park, Carramar, Villawood, Leightonfield, Chester Hill, Sefton, Birrong and Yagoona.

The new Metro line is expected to open in 2024.

Roydon Ng, from community group "Restore Inner-West Line" said the impacts would be "devastating" to young people who work and study in the city.

"They will be isolated from the rest of the Sydney Trains network, having to change for the first time ever since the rail network was built," he said.

Kaashif Ahmed says it will take him an hour to get to work. ( ABC Image: Greg Miskelly )

IT professional Kaashif Ahmed relies on a 38-minute express train from Birrong to Town Hall to get to work.

His said his new trip would take over an hour, with two line changes required — the first at Bankstown onto the Metro, and then another at Sydenham back on to the heavy rail line.

"If that change comes in, I have to take three trains to reach Town Hall, which is such a pain for me," he said.

Helen Huynh, a health sciences student at Sydney University, said she was also losing her direct connection from Yagoona to Redfern.

She said the NSW Government's plans would "inconvenience" people in her area.

"The communications have not been effective for this multicultural community," she said.

"There is a lot of Vietnamese people in this area.

"And they haven't been shown any Vietnamese language communication as to what's happening."

A NSW Government submission to the inquiry said the changes would help deliver a 60 per cent increase in rail services.

"Sydney Metro, together with signalling upgrades across the existing Sydney rail network, will increase the capacity of train services entering the Sydney Central Business District — from about 120 an hour today to up to 200 services beyond 2024," it said.

Helen Huynh's direct service from Yagoona to Redfern is going to be cut. ( ABC Image: Ross Byrne )

Sydney University submitted data to the inquiry showing more than 3,500 students and staff who "live within 2km of stations" would be disrupted.

Greg Robinson, the university's Director of Campus Infrastructure, told the ABC "continuing with Redfern Station" as the sole rail option for the university was "not a sustainable strategy".

"Students and staff living west of Sydenham will face about 15 per cent extra travel times, while those using the T3 limited stops service will face up to 26 per cent longer travel times each way," he said.

He said a proposed Metro stop at Camperdown, which was rejected by the NSW Government, was sorely needed.

Sydney Trains CEO Howard Collins said converting the line to a Metro service would "disentangle" the city's congested heavy rail network.

"Removing this branch line from the existing railway makes the system operate more efficiently, delivers benefits far and wide and removes a bottleneck," he said.

The inquiry also probed whether some railway stations may close after the Metro opens — something that remains unclear.

A spokesperson for Sydney Trains said there was no plan to close any of the nine stations in 2024.

"Customers not served by Metro will continue to receive suburban train services once Sydney Metro City and Southwest commence operation" the spokesperson said.

Sydney Trains was also approached to confirm what new blueprints are being developed for the lines.