Metro, commuter rail, light rail or tram: how to tell city trains apart

What separates a metro from commuter rail, light rail, a tram or an airport link, explained with the Yamanote Line, BART, Roslagsbanan and GONOM's subway maps.

Why the names get confusing

Metro, subway, underground, commuter rail, S-Bahn, light rail, tram: the words are used loosely, and they mean slightly different things from one country to the next. Behind them, though, sit a few practical questions that any passenger can ask. Does the train have a track of its own, or does it share the street or the main line? Does it come every few minutes, or does it run to a timetable? How far apart are the stations, and how far out of the city does the line go?

Answering those questions tells you more about a line than its name does, and it explains why several of GONOM's urban cab rides are hard to put in a single box. This guide works through the main categories one at a time, using those videos and the city maps as examples. It does not explain how the maps themselves are drawn; that is covered in GONOM's guide to why subway maps look the way they do.

Metro: a track of its own and trains every few minutes

UITP, the international association of public transport, defines a metro as an urban guided electric transport system with high capacity and frequency of service. The key feature is an exclusive right of way. A metro never meets road traffic or freight trains, so it can run frequent trains on short headways, and passengers simply turn up instead of checking a timetable. Stations are close together and mostly inside the built-up city, usually in tunnels or on viaducts.

The networks on GONOM's subway maps, from the Paris Métro to the Seoul subway, are built this way. Copenhagen shows the idea in its purest modern form: four lines with their own tracks, meeting at Kongens Nytorv, and at Nørreport connecting with the S-trains, the city's commuter rail. On any of the maps, a dense web of short, closely spaced stops inside the city is the visual sign of a metro; long lines reaching far into the suburbs usually mean something else.

Commuter rail, and why the Yamanote Line breaks the rule

Commuter rail links a city centre with its suburbs and outlying towns. It usually runs on main-line track with main-line trains, often shares that track with intercity and freight services, runs to a published timetable and has stations further apart. Names vary: S-Bahn in German-speaking cities, RER in Paris, S-tog in Copenhagen. The line between commuter rail and metro is not sharp. In central Paris the RER runs through frequent underground corridors, and Japanese commuter lines often work much like a metro.

The Yamanote Line is the clearest case. It is a JR East railway, not part of Tokyo Metro or Toei, which is why it does not appear on GONOM's Tokyo subway map. Its eastern half borrows the corridor of the Tōhoku and Tōkaidō Main Lines. Yet it behaves like a metro: 30 stations on a 34.5 km loop, with trains as often as every two minutes at peak. In the cab video, watch the eastern side, where the Keihin-Tōhoku Line runs on parallel tracks and the Shinkansen viaducts stand close by, and notice how short the gaps between stations are.

BART and Roslagsbanan: lines that sit in between

BART is classed as rapid transit, the American term for metro, and under Market Street in San Francisco it looks like one. But the Yellow Line runs about 100 km from the airport to Antioch, and east of the Berkeley Hills the stations are far apart and the track often sits in the middle of a freeway. BART uses an unusual 1,676 mm broad gauge, so its trains could never share track with main-line railways. At Pittsburg/Bay Point the video shows a change to eBART, a standard-gauge extension with different trains, so one ride covers a metro, something close to a suburban railway, and a third kind of train at the end.

Roslagsbanan in Stockholm is harder still to label. It is a 65 km narrow-gauge network on 891 mm track with three branches, owned by the county rather than the national rail network. Encyclopedic sources call it a suburban or commuter railway, while SL, Stockholm's transport authority, shows it as light rail on its maps. Passengers change to the metro at Tekniska högskolan. In the video, watch the double track as far as Vallentuna give way to single track, passing loops and small country halts.

Light rail and trams: where the track runs

UITP describes light rail as a rail-borne form of transport that can be developed in stages from a modern tramway to a rapid transit system, and it may run underground, at street level or on viaducts, usually on its own right of way. A tram, or streetcar, is the version that shares road space with cars and buses. The vehicles can be almost identical; the difference lies in the track. A useful rule is that light rail which leaves the street becomes more like a metro, and light rail that stays in the street is a tram.

The Busan–Gimhae line on GONOM's Busan map shows how little the word light can mean. It is called a light rail transit, yet it is driverless and fully separated from traffic, and Railway Gazette described it on opening as a driverless metro. It opened in September 2011 and runs 23.5 km with 21 stations, from Sasang in Busan to Kaya University in Gimhae. Light, here, refers to shorter trains and smaller capacity, not to the way the line is built.

Airport links, and a ride that is not transport at all

An airport link is not a separate technology. It is any of the types above, aimed at a terminal. BART reached San Francisco International Airport in 2003, and the Yellow Line video starts in the airport station, so arriving passengers ride a metro straight under downtown. Oakland's airport is served by a different system: since 2014 a short automated guideway, built with cable-car technology from Doppelmayr, has linked it with the BART network; GONOM's San Francisco map draws it as the Grey Line. In Busan, the light rail line itself passes through Gimhae International Airport.

Haeundae Blue Line Park is a useful last example because it is not public transport. It reuses 4.8 km of the old Donghae Nambu Line, which main-line trains left in 2013. The Beach Train runs on the original track, and the Sky Capsules in the GONOM video glide above it at about 4 km/h. In the film, look down at the old main-line track below the capsule: the commuter trains that replaced it now run inland on the rebuilt Donghae Line, which meets Busan Metro Line 1 at Bujeon.

Watch these journeys on GONOM

Subway maps mentioned

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