The booming outer-northern suburb of Mernda will be connected to the rail network, regardless of which party wins the state election.

On Tuesday morning the Coalition matched Labor's promise to extend the railway from South Morang out to Mernda, pledging to build it for $700

million by 2020-21.



The planned 7.5 kilometre double track extension will see extra stations built in South Morang and Mernda. Trains will begin running every 10 minutes from next year on the line.



The stations will provide another public transport option for one of Melbourne's fastest-growing areas, where rapid population growth has choked roads in Mernda and neighbouring suburb Doreen. Whittlesea Council says 9500 people move to the area each year.



The announcement marks a victory for locals who have campaigned strongly for a railway extension past South Morang. A Mernda rail Facebook page has more than 6000 likes.



Premier Denis Napthine said the promise hadn't been made because of the seat of Yan Yean's 0.1 per cent margin but because of the population growth in the area.



"When this is completed, we will be delivering train services to Mernda every 10 minutes off peak," he said.



Labor made its promise in September and said the extension would cost between $400 million and $600 million. They committed to having the service up and running in their first term.



Transport Minister Terry Mulder said the two stations would be premium stations and staffed from first to last train. He said Labor's plan was underfunded and hadn't been properly planned.



"We're not going to promise what we can't deliver," he said.



Darren Peters from the South Morang and Mernda Rail Alliance said locals had been waiting for the announcement for a decade.



He said he didn't mind ultimately which party's plan was successful as long as the railway extension was delivered.



"We had the community behind us but it was definitely the marginal seat status that tipped us over the line," he said.



Mr Peters did raise concerns over the 200-capacity car parks at each station and said they might need to be expanded down the track.



Mr Mulder said the plan was to build what was needed and that more people were expected to travel to the station by bus.



The pledge forms part of a suite of $815 million in Coalition transport promises for the marginal seat, including $95 million to duplicate a 3.9 kilometre stretch of Yan Yean Road.



The single-lane road carries 20,000 vehicles a day and has become increasingly bottlenecked at peak times.



Whittlesea mayor Mary Lalios described it as a "fantastic day" for the local community and said it was important that all parties had committed to the project.



"It means that people will be able to access jobs, they will be able to access schools, everything they need to run their daily lives," Cr Lalios said.



Yan Yean is the most marginal seat in Victoria. Currently held by Labor MP Danielle Green, a recent redistribution left the seat notionally Liberal at 0.1 per cent.



Ms Green said the promise was a "last-minute stunt" which "smacked of desperation".



"Denis Napthine and the Liberals have done nothing for four years in the northern suburbs," she said.