The unveiling of Melbourne Metro should be followed immediately by a city loop reconfiguration, according to a major infrastructure advisory body.
Infrastructure Victoria on Wednesday released a draft 30-year strategy in which it said Melbourne's train network is nearing capacity and will not support many more services entering the city loop.
The report said even with completion of the Melbourne Metro tunnel project by 2025 and a proposed Melbourne Metro Two, the Craigieburn and Upfield lines would soon reach capacity.
This, it said, was due to increasing demand driven by the expansion of the northern growth corridor beyond Craigieburn to Donnybrook, Beveridge and Wallan.
In response, Infrastructure Victoria recommended redesigning two of the four city loop tunnels to allow more trains to pass through the city and continue.
A redesigned city loop would create a pair of underground cross-city tracks from Richmond to North Melbourne.
But the project would need to be constructed immediately after the Melbourne Metro tunnel is opened, Infrastructure Victoria said.
"The window of opportunity to deliver the project will close as demand continues to increase," it said.
"And the network may only temporarily have enough spare capacity to change train service patterns during construction to minimise passenger impacts."
Infrastructure Victoria recommended separating the Craigieburn and Upfield lines as they ran through the city before potentially running onto the Frankston or Glen Waverley lines.
This, it said, would mean they did not have to share the same city loop track, allowing for increased capacity and reliability.
Infrastructure Victoria chief Michel Masson also welcomed the state government's announcement earlier this month it would introduce cheaper off-peak fares for public transport users from February as the COVID-19 recovery takes off.
The three-month discount, which will see passengers save 30 per cent on fares between 9.30am and 4pm or after 7pm on weekdays, will cost the state government between $7-15 million.
But Mr Masson recommended these off-peak fares become a permanent fixture in Melbourne, as well as offering cheaper fares for buses and trams at all time.
A Victorian government spokeswoman said the city loop timetable restructure, announced at the same time, would create extra capacity for more than half a million passengers per week.
She said space would be freed up in the city loop as the Cranbourne, Pakenham and Sunbury lines travel through the Metro Tunnel.
"Infrastructure Victoria's draft strategy supports the government's work already underway in delivering vital upgrades to our transport networks and we look forward to seeing the final report," the spokeswoman told AAP.
She added that the Metro Tunnel had to be built before any future projects, such as Metro Two, were conducted.
Among its 95 recommendations to the Victorian government, the draft strategy also suggested changes to improve the energy performance of housing.
This included requiring all new homes to achieve a minimum 7.0 in the Nationwide House Energy Rating Scheme.
It also included a statewide mandatory energy rating scheme, designed to give potential buyers or renters the chance to choose a lower cost, more efficient new home.