The Milan Metro subway system is managed by a single ATM control centre, built in 2013 by Alstom.
Lines 1 and 2.
Line 2 uses a speed signaling system. Trains are directed using light signals with five aspects:
Before 2011, Line 1 used this same system, but now uses a new signaling apparatus. The signaling apparatus permits a 90-second frequency on the line, allowing for additional capacity, especially at rush hour, similar to the one used on the M3 line. The speed of the train is decided by an ATC system and a two-color semaphore system. 
The two-color semaphore system has three possible states:
Line 3.
Line 3 has an ATO/ATP system, so the driver must only check the doors and give consent to the electronic system to start the train.
Lines 4 and 5.
Lines 4 and 5 use AnsaldoBreda Driverless Metro, consequently the lines do not have classical light signaling. Automatic signaling permits a frequency of a train every 75 seconds, but on Line 5 only a 150-second frequency is used, owing to the lack of big enough depot for the number of trains that would be needed; this may get fixed as the line gets its own depot, along with its planned extension into Monza.