Rome has an extensive transit system operated by ATAC that includes buses, subways, and tram lines. Combined across all these modes, ATAC serves 4 million passengers each day. The bus network consists of 490 lines and more than 2,700 buses. A single trolleybus line has been in operation since 2005, but Rome previously had trolleybuses from 1937 until 1972. The subway system consists of three lines with a fourth in the design phase (as of 2015), the first line opened in 1955. Today, the Metro has about 37 miles of track and 73 stations. The tram system consists of six lines, however, this is merely a small remnant of what was once the largest tram system in all of Italy. Some of the active fleet has been in service since the late 1940s.
As is the case in many European cities, all fares are paid via the honor system and are valid for unlimited transfers within a set period of time.
Although Line A opened after Line B, it is called Line A because it was originally the longer of Rome's two subway lines. Line A first opened in 1980, operating from Anagnina to Ottaviano. The line was extended to Viale Aurelia on May 29, 1999, and to Battistini on January 1, 2000. The line is now 11.8 miles (19 kilometers) long, all of which is underground aside from when the line crosses the Tiber River between Flamino and Lepanto, has 27 stations. The line is served by CAF MA300 Stock. These Spanish built trainsets have articulated cars that allow easy movement from one railcar to the next, automated announcements, LED displays that show the name of the next station, TV screens in each car, and CCTV.
Rome Metro Line B was the first of Rome's two subway lines to open. The initial section, from Termini to Laurentina, opened in 1955. In 1990, the line was extended to the northeast, to Rebibbia. As of 2015, Line B has 26 stations along 14.7 miles of track, including the recently opened branch to Jonio. Line B is served by Breda built MB100 Stock; the stock was starting to undergo a rebuilding program as of 2008. In 2010, new stock, similar to the stock used on Line A, was delivered.
The "historic" Stanga trams were manufactured in 1949-1950, and still run on lines 3, 5, 14, and 19 each day. These cars are single ended, so they are unable to operate on the newer Line 8 that does not have loops at each end to turn the trams around. The Viberti built trams look very similar to the Stangas, but they are numbered in the 7100 series and are slightly longer than the Stangas.
Socimi built 35 double ended trams before going out of business in the early 1990s. In addition to being Rome's first double ended trains, they were also the first low floor trams to operate in the city. However, they were not fully low floor trams. As a result of the Socimi company going out of business, the Fiat trams were ordered at the end of the 1990s.
The Fiat-I and Fiat-II trams were ordered at the end of the 1990s after the Socimi company went bankrupt before finishing the manufacture of Rome's first low floor trams. Like the Socimi trams, the Fiat-Is are partial low floor trams, and began to arrive in 1999. Currently, there are 28 Fiat-I trams in operation. An order for 50 fully low-floor trams was placed shortly after the Fiat-Is began to arrive. Known as Fiat-IIs, these trams entered service in 2000. Both the Fiat-I and Fiat-II trams are double ended with doors on both sides of the vehicles, and can operate on any of the city's tram lines.
ATAC has a fleet of 53 electric powered TecnoBus Gulliver buses. These buses are assigned to circulators in Central Rome that operate on streets that are too narrow for standard sized buses. Additionally, because these buses' electric engines are so quiet, they do not create noise pollution that might be harmful to old structures in the ancient city center. These buses were pulled from service in 2014 due to fires breaking out on the vehicles. Rome announced in 2018 that the municipality had reached an agreement with TecnoBus to "revamp" the buses that were idling in the depots upon being removed from service.
Rome had trolleybuses from 1937 until 1972, and again since 2005. The current fleet of 30 Solaris trolleybuses operates on Route 90 between Stazione Termini and Largo F. Labia. Because it was thought that overhead electric wires would negatively impact the streetscape within the city center, from Termini to Porta Pia, the buses are powered by on board batteries that recharge as the bus runs on the section of the route with overhead wires.