Public transport fares in Victoria will be capped at $30 a week if the Labor government is re-elected next month – but commuters will need to dust off their Myki cards to benefit.

The premier, Ben Carroll, on Monday said the fare cap would begin on 1 January, the day after half-price fares end. The discounted fares were introduced after a period of free public transport in response to the fuel crisis sparked by the US-Iran war.

A $15 cap would also be introduced for concession-card holders, while exisiting benefits – including free public transport for children and free weekend travel for seniors – would continue.

Carroll told reporters the new cap would save regular commuters up to $1,400 a year.

“[This is] real important cost-of-living relief, in a time of rising interest rates and increased petrol prices,” he said.

But the state’s public transport minister, Vicki Ward, said commuters must use Myki cards to access the capped fares.

This is despite the government completing the rollout of tap and go payment across the public transport system last week, when concession card holders were able to pay using a bank card, smartphone or smartwatch.

“We’ve never advised people to throw out their Myki card. So I’d suggest they have a look in the back of the couch and find their Myki card if they need to,” Ward said.

She said the government would to make the $30 cap accessible via tap and go “as quickly as possible”, but would not provide a date.

Carroll said the cap would cost the government $206m and would run for two years until December 2028.

The government said the cap was not sustainable in the long-term and would be funded through “commonsense decisions to reduce spending” in other areas.

The announcement was welcomed by the Swinburne university transport expert Prof Hussein Dia, who said it would provide households with certainty during the cost-of-living crisis. But he said the benefits would not be equitable.

“The greatest benefits will naturally go to people who already have good access to trains, trams, buses, and travel frequently,” Dia said.

“People in outer suburban areas with poorer public transport may receive much less benefit, even though they may face equally strong cost-of-living pressures.”

Juanita Pope from the Victorian Council of Social Service said the organisation had long called for cheaper public transport.

“A fare cap is good policy on many fronts: good for household budgets, road congestion, and the climate,” Pope said.

The Greens leader, Ellen Sandell, urged the government to go further and make public transport free.

“After 12 years in government, Labor is only offering Victorians a temporary discount with an expiry date after the election,” she said.

“People are sick of paying more and getting less. We need more frequent, reliable and accessible trains, trams and buses that people can actually depend on.”

The commitment follows Labor’s pledge on Sunday to cap road tolls at $30 per week for a year, saving drivers who regularly use them as much as $5,000. The Coalition had previously committed to a $50-a-week toll cap if elected in November.

“Imitation is the best form of flattery,” the opposition leader, Jess Wilson, told reporters on Sunday.

She said Labor could not be trusted to lower tolls, given they had consistently increased them in their 12 years in government.

“Victorians are paying higher tolls today as a direct consequence of the decision making of this Labor government, and you simply cannot trust them now, five minutes to midnight, that they’re going to reduce tolls,” Wilson said.