On 12 October 2024, the entire Line 4 of the Milan metro, known as the Blue Line, was inaugurated. This represents one of the most significant investments for the city, with more than 1.5 billion euros earmarked for its construction. The fully automated, driverless line stretches 15 km, connecting Linate airport with San Cristoforo station, passing through 21 stations through the heart of the city. It is estimated that Line 4 will carry around 86 million passengers each year, removing around 30 million car journeys from the streets of Milan, with a resulting reduction of 20,000 tonnes of CO₂. The transport system operates with high-frequency trains, passing every 90 seconds during peak hours, ensuring a fast and continuous service. In terms of sustainability, Line 4 stations are designed with green criteria: LED lighting, recycled materials and energy recovery technologies, contributing to the reduction of energy consumption. Besides reducing CO₂ emissions, the project will also reduce noise pollution, thanks to quiet trains and the use of sound-absorbing materials. With the completion of the Blue Line, connectivity between strategic areas of Milan, such as Linate airport, the city centre and the San Cristoforo district, has received a significant boost, reducing travel time to around 30 minutes between the two termini. This line is now a key element for sustainable mobility in Milan, also promoting the creation of thousands of new jobs and encouraging a modal shift towards public transport.