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Case Study:

Metro Line M4 in Milan

The design of the M4 metro line facilitates seamless integration with various collective mobility systems, effectively intertwining relationships between surface and underground infrastructures. The multidisciplinary approach led to an innovative, safe, and inclusive result that engages in a constructive dialogue with the legacy of designers Albini and Norda. Their pioneering work laid the initial groundwork for Milan’s MM1.

Linea metropolitana M4 Milano - Fermate

The line

The M4 extends from the San Cristoforo station to Linate Aeroporto for a total of 21 stations. (Fig. 1) As it traverses from the western to the eastern outskirts, nearing the city center in the central section, the route is intricately divided into functional lots with distinct construction priorities. Policreo has played a pivotal role, developing functional and architectural designs for 7 stations, including San Babila, Tricolore, Susa, Argonne, Forlanini FS, Repetti, and Linate Aeroporto. Our expertise extends to related shunting rods, the Idroscalo ventilation building at the line’s eastern end, and surface and road systems for Forlanini FS and Linate Aeroporto stations. We’ve crafted designs for finishes, integrated furnishings, and user orientation signage across all 21 stations. The structural design of Forlanini FS and Linate Aeroporto stations, both underground and above-ground, along with two interlocking structures, is also part of the project.

Dimensions :

  • 15 kilometres long from Linate Airport to San Cristoforo FS
  • Light and fully automated metro (driverless)
  • 24,000 passengers per hour per direction
  • Commercial speed 30 Km/h
  • Maximum speed 80 Km/h
  • Capacity of 600 passengers per convoy
  • 40 vehicles in operation during rush hour (plus 7 escort vehicles)


The stations are divided into 10 surface stations, 6 deep stations and 5 with atypical characteristics. The typical surface stations are underground, on three levels (atrium/ mezzanine level, platform level and technical/under platform level), below the existing road system, with a minimum of 2 accesses from the urban level.

Relation with the territory

Our integrated design solutions blend surface and underground environments, ensuring a consistent identity for the entire infrastructure. This fosters recognition for both occasional and frequent users while maintaining appropriate connectivity with the city. We interpret and preserve the unique characteristics of diverse urban contexts, establishing an evocative and relational dialogue

Ceramic tiles

We’ve used advanced ceramic materials, specifically Cotto d’Este’s large porcelain stoneware tiles, for durable and easily sanitized surfaces. The large tile format enhances aesthetics and simplifies maintenance by minimizing gaps. The color palette, inspired by chalk and clay, complements the underground surroundings. Lighter tones create a sense of space in passages and stairs, while darker hues define more expansive areas like atriums. This color rhythm enhances both outer and inner urban surfaces, improving spatial perception. The tile patterns dynamically guide through the station, with dark surfaces marking city contact points and light ones signifying underground spaces.

Special elements

The station design is based on positive behavioral models from Environmental Psychology.
The expressive language in architecture enhances user experience and safety, positively interacting on aesthetic and emotional levels.
User areas feature durable, easy-to-maintain, and eco-friendly finishes, ensuring flexibility and reproducibility over time

Linea metropolitana M4 Milano - San Babila


To ensure a positive experience in our mobility spaces, we’ve curated physical elements with soothing tones and dynamic designs for effective orientation in underground environments. Contrastingly, emotionally charged claddings featuring ideograms evoke urban elements, establishing a psychological connection with surface reality and enhancing the waiting experience. Even functional spaces, like access tunnels and platforms, are designed to transform movement into an architectural journey, redefining it as a key element of local identity.

Streamlined Signage

Our signage project builds upon Noorda and Vignelli’s concepts with adjustments for optimal legibility. Adhering to the ‘Manual of Signposting for the Stations of the Milan Underground,’ we’ve crafted an organic organizational framework, incorporating the latest in information graphics for public transport infrastructures. We’ve established a hierarchical criterion based on the relationship between each piece of information and its specific transmission point, considering user flows and perceptions. Signage organization reflects passenger needs, guiding them seamlessly from surface roads to underground platforms. In line with adaptability, information is tailored to three user categories: general users, disabled users, and cyclists.

Enhanced Accessibility

The focus on accessibility revolves around eliminating architectural barriers. Embracing a global interpretation of mobility, the projects aima to create a universally accessible and usable physical environment. Specifically, we’ve developed ‘autonomous mobility’ solutions for various disabilities, with a dedicated study on the movement of individuals with visual impairments. Orientation, a complex cognitive-perceptual process, is addressed through thoughtful design. Routes are meticulously planned, featuring signage, landscaping, and a tactile-planar “LOGES” (Guide Orientation And Safety Line) system. This system complies with current regulations, ensuring seamless movement for all individuals, from urban environments to metro service areas.

Transformative Impact:
The M4 will revolutionize the mobility in Milan with:

  • 118 km of line
  • 136 stations
  • A 34% network increase in a decade.

By 2023, Milan’s metro network ranked sixth in Europe, aligning with major European capitals. The full M4 launch is projected to cut daily urban traffic by 180 thousand vehicles, reducing annual CO2 emissions by up to 75 thousand tonnes. A game-changer for sustainable urban living.


Recognition at “La Ceramica e il Progetto 2022”
Our project earned acclaim in the Institutional category at the 11th edition of the international competition. The choice of Cotto d’Este porcelain stoneware tiles seamlessly aligned with the original design, fostering an expressive language that engages users aesthetically and communicatively
Sito del concorso: https://laceramicaeilprogetto.it/menzione-istituzionale-2022/