Marginal seats ensure the Frankston railway line attracts a lot of government spending. Credit:Paul Jeffers It's an about-face from the government's approach to the Cranbourne-Pakenham line, where the decision to build elevated rail to remove nine level crossings was made without meaningful consultation. But it's no surprise given the Frankston line passes through a string of marginal seats Labor will need to hold in 2018 if it is to be re-elected. So at all but three of the 13 level crossing sites, the government will bury the rail line under the road, no matter the likely greater expense. Trenches will be dug in Edithvale and Bonbeach, where the line is on a former swamp and just 100 metres or so from the shoreline, and in Mentone and Cheltenham, where the compulsory acquisition of 32 properties will add millions to the project cost. A rail bridge would have involved just eight property acquisitions. At Carrum this week, Public Transport Minister Jacinta Allan declined to say if the government had already blown its $2 billion budget for the Frankston line works, but its decision to dig a trench wherever possible surely increases its prospects of doing so. Which is better, rail under or rail over is up for debate, but bayside residents' determination to fight for the outcome they want, whatever the cost, is easy to understand.

A protester at a rally against a sky rail on the Frankston train line. Credit:Jason South Melbourne's growing pains as it stretches beyond 4 million are felt by everyone. But population growth hasn't altered the city's essential character, which is less heaving metropolis than a series of fiercely parochial villages, each stubbornly protective of its patch and disinclined to take one for the team when issues of wider city planning are concerned. This is a wicked problem for government, which must take a holistic view about investing in a rail system experiencing growth in demand of almost 3 per cent a year, without riding roughshod over local interests. But it's increasingly apparent that the Andrews government has not got the balance right with the Frankston line, such is its anxiety about keeping its grip on four marginal seats it holds by margins as thin as 0.5 per cent. Consider for example that Melbourne hasn't had a major update to the metropolitan train timetable since Labor was elected almost 2½ years ago. The government has never publicly explained its reasons for deferring the update, although a leaked copy of what was planned revealed it involved removing several peak-hour Frankston services from the City Loop, which would have inconvenienced some commuters. The decision also meant the addition of badly needed peak-hour services for some of Melbourne's most overcrowded lines, including Werribee, Craigieburn and Sunbury, has been deferred.

The timetable update is an increasingly (and literally) pressing matter for commuters on those lines, which, as it happens, run through safe Labor seats. This is galling given the capacity to add extra services has been there ever since the $3.65 billion Regional Rail Link opened in mid-2015, freeing up dozens of train slots that V/Line used to need. At least the Andrews government can argue it's not the first to squander cash on the Frankston line. The former Baillieu/Napthine Coalition government, also anxious to sandbag four newly Liberal Frankston line seats, spent $115 million on the so-called Bayside Rail Project, whose chief benefit was introducing X'Trapolis trains, the system's "newest, biggest and fastest" trains, to the line. It wasn't enough to stop voters in those seats swinging back to Labor in 2014, and any reference to the project has already been scrubbed from PTV's website, even though it was only completed late last year. The need for bigger trains to Frankston was questionable, given the line does not have a serious overcrowding problem, while the trains' superior speed was moot given the Coalition had also padded out the timetable so it could get the trains to run on time. So while commuters on the Frankston line have cause to reflect on the perks of living in a marginal seat, commuters on some other lines can only dream of ever getting a seat at all.

Adam Carey is The Age's transport writer.