Cranbourne and Pakenham line commuters travelling to South Yarra would save up to 10 minutes' travel time if the Melbourne Metro rail project included the station in the multibillion-dollar project, documents show.
The Andrews government has already ruled out creating an interchange at South Yarra for the Cranbourne and Pakenham lines.
The two lines will instead bypass the station – the 11th busiest in the network – and travel direct through a tunnel to a new station near St Kilda Rd and on to new CBD stations, Parkville and North Melbourne.
The cost of adding an interchange station is almost $1 billion and has a poor cost-benefit ratio.
Modelling completed for Public Transport Victoria shows that if there were an interchange, 14,000 people travelling direct to South Yarra would save up to 10 minutes on their commute.
If South Yarra was included in the Melbourne Metro project it would add an extra minute to 100,000 people's daily journey into the city.
"Over 100,000 customers per day would be a minute worse off if the South Yarra Interchange Station is included, compared to less than 14,000 customers who would be between one and 10 minutes better off," the PTV document says.
"In aggregate (i.e. taking into account all journey time savings and all slower journey times), the addition of a new station at South Yarra would add an additional 1500 hours of travel time per day for public transport users in 2031."
The PTV document, released under Freedom of Information, shows that around a third of travellers alighting at South Yarra come from the Dandenong line.
The document says that "overall, the proposed new South Yarra interchange station delivers a poor outcome, with an estimated incremental Benefit Cost Ratio of 0.2."
The government announced earlier this year that it would not build an interchange for South Yarra, which the Greens and Coalition have lobbied for, because it would cost up to $970 million, require more than 100 properties to be acquired and be of little benefit.
Greens Prahran MP Sam Hibbins said commuters would be worse off without a Melbourne Metro interchange at South Yarra station. He said the longer travel times were "unacceptable".
"Whether you're travelling to or from South Yarra, or using the station to interchange between lines, commuters will be worse off," Mr Hibbins said.
"A South Yarra interchange will assist the thousands of fans travelling to the MCG and sports precinct who would all otherwise have to interchange at Caulfield."
Minster for Public Transport Jacinta Allan said an additional connection at South Yarra would cost close to $1 billion, destroy more than a 100 extra properties and be of little use to South Yarra locals.
"Melbourne Metro will deliver huge benefits to South Yarra, relieving congestion at the busy station and enabling more frequent and reliable trains from Sandringham and Frankston into Flinders St and the City Loop," Ms Allan said.
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