Commuters from Sydney's waterfront suburbs who frequently use ferries will be among the biggest beneficiaries of the Berejiklian government's promise to lower the weekly cap on fares for public transport to $50.

With cost-of-living pressures a key election issue, the Coalition has vowed to cut the weekly cap on Opal fares by 21 per cent from $63.20 to $50 if it is returned to power.

Ferry users will be among the biggest winners from a cut to the weekly Opal fare cap. Credit:Michele Mossop

They argue up to 55,000 commuters will benefit from the lower cap and thousands will save up to $686 a year.

While long-distance train commuters will be beneficiaries, Sydney University senior transport lecturer Geoffrey Clifton said ferry users would be among the biggest winners.