Twenty-three road bridges and underpasses in Sydney's west will need to be upgraded or rebuilt to enable the Bankstown rail line to be converted to carry metro trains, posing significant disruption to already congested streets during construction.

The overhaul of the bridges will add to the upheaval on local roads from extra buses required to transport thousands of commuters while a 13.5-kilometre stretch of track between Sydenham and Bankstown is closed for construction.

Residents along the rail corridor have also been warned they will be affected by noise and vibration, some of which will occur at night during the four-year construction period. Marrickville, Dulwich Hill and Bankstown will be among the suburbs worst affected by noise because of the closeness of homes to the line.

Under the latest plans for the project, 18 bridges, five underbridges and three footbridges along the line will require work to bring them up to scratch, much of which will happen at night and during weekends when traffic tends to be lighter.