The M6 will be Milan’s first metro line that does not pass through the centre

A sort of Circle Line like Berlin’s Ringbahn, capable of connecting suburban neighbourhoods without passing through the centre, but also an extension of the M2 towards Gratosoglio, Rozzano or Buccinasco. Or a metro-rail system integrating the Passante, suburban lines and existing infrastructure.

Today, more than twenty years after the first hypotheses, the M6 — Milan’s future pink line — finally seems to be getting closer to reality. But its definitive route is still entirely to be decided. And this time, alongside Palazzo Marino, citizens, associations and committees will also discuss it as part of the new participatory process launched by the Municipality.

With the completion of the M4 in autumn 2024, the M6 has become the new big topic in Milanese public transport. Building a new heavy metro entirely from scratch would require huge investments and very long timeframes. For this reason, three different hypotheses are currently being compared, each with its own advantages and limitations.

The most ambitious proposal is that of the orbital line: a sort of metro Circle Line inspired by the Berlin Ringbahn, an underground ring or semi-ring capable of connecting peripheral neighbourhoods without crossing the centre. The idea is to finally create transversal connections between areas such as Certosa, Bovisa, Città Studi, Lambrate, Romolo or Famagosta, relieving pressure on existing lines and reducing dependence on central hubs.

The main advantage would be imagining a more polycentric city that is less focused on the historic centre. The limitation, however, is the very high cost of a completely new, entirely underground infrastructure.

More pragmatic is the hypothesis of turning the southern branch of the M2 into a new M6, extending it beyond Piazza Abbiategrasso towards Gratosoglio, Rozzano or Buccinasco. In this case, part of the existing network would be reused, quickly serving highly populated areas that currently have poor rail connections. This is a faster and cheaper solution, but also less transformative for the overall structure of urban mobility.

The third option is the so-called “metro-railway”: a hybrid system that would integrate suburban lines, the Passante railway and existing infrastructure into a model closer to the German S-Bahn than a traditional metro. In this scenario, the M6 would not necessarily be a new line dug entirely underground, but an integrated network capable of exploiting tracks that are already present, limiting new construction sites and costs. It is probably the cheapest and fastest solution, but also the most difficult for users to read and to transform into a truly recognisable line.

For now, there is no definitive route or official decision. The Municipality of Milan, MM and the Ministry of Infrastructure are working on preliminary studies and cost-benefit analyses to understand which scenario is the most sustainable.

The novelty of recent months is that Palazzo Marino has launched a public participatory process dedicated precisely to the future M6, presented in the municipal Mobility and Participation commissions. The Municipality has published a notice to select the operators responsible for organising public meetings, listening activities and consultations with citizens, associations and stakeholders. The process, which is expected to last about eight months, will accompany the development of the line’s possible design scenarios.

According to the Municipality, the public debate will also serve to guide the final choice of the route. The process will distinguish between “fixed nodes” — such as interchanges with existing metro and rail lines — and “mobile nodes”, on which discussion can be opened with the local areas involved. Palazzo Marino has also hinted that the future M6 could be built in successive phases, first identifying a definitive route and then a first priority section to be constructed.

The first hypotheses for a sixth metro line in Milan date back to the late 2000s and imagined a new “classic” line: an entirely underground northwest-southeast axis, with interchanges with all other lines and crossing through the historic centre. Behind the project, however, a structural problem of Milanese mobility was already emerging: the metro network had been built as a radial system, in which almost all lines converged towards the centre. It was a model that was already starting to show its limits back then, and which today appears increasingly unsuited to an ever more polycentric city.

Mind, Santa Giulia, Scalo Romana, Bovisa, Rozzano, Buccinasco: these are just some of the areas that still remain poorly served by the metro network today. Moving between semi-central or peripheral neighbourhoods — for example between the west and south or between the north and east — still very often means having to pass through the centre, change lines and go back. In 2022, with the launch of feasibility studies funded by the Ministry of Infrastructure, the debate shifted direction: the issue is no longer just building a new line, but understanding what type of infrastructure can be useful for a Milan that has changed in the meantime.

Today, the debate is therefore not only about the route of the pink line, but about the model of mobility and the city that Milan wants to build over the coming decades: whether to continue expanding a traditional radial network or to focus on a more orbital, metropolitan and European system, designed for a city where citizens pass through the centre less and less.

Opening image: render of the M6 metro in Milan. Via r/milan reddit