Rapid transit

• 1. Introduction

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  Rapid transit moves more people through a city than almost any other machine on earth, and yet most riders never see how strange its engineering really is. In Hong Kong, MTR Corporation's urban lines carry between 75,000 and 85,000 people per hour. A single typical line, by contrast, manages around 36,000 passengers per hour per direction. The world's first such system, the partially underground Metropolitan Railway, opened in London in 1863 using steam locomotives. It now forms part of the London Underground. Why does one city call it the subway, another the tube, another the metro, and still another simply the T? Why was the deepest system on the planet built in marshland, with stations more than a hundred metres down? And how did trains learn to run with no driver at all? The answers run underground, overhead, and through a century and a half of choices about how a city should move.

• 2. A World Of Names

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  In most of Britain, a subway is not a railway at all but a pedestrian underpass. The same word, in North America, names the rail systems of New York City and Toronto, the only two on the continent primarily called subways. Names follow the medium passengers travel through. Tunnels inspire subway, underground, the German Untergrundbahn or U-Bahn, and the Swedish Tunnelbana or T-bana. Viaducts inspire elevated, skytrain, overground, and the German Hochbahn. The term Metro is the most common word for underground systems among non-native English speakers, drawn from the idea of the metropolitan area itself. France's large cities use metro, from Paris and Lyon to Marseille and Toulouse, while smaller Lille and Rennes run a light metro. In Eastern Europe the word bends to local tongues, becoming mietrapaliten in Minsk and metropoliten in Kyiv and Moscow. Boston's system is known locally as The T, while Atlanta's goes by the acronym MARTA and the San Francisco Bay Area's by BART. The New York City Subway keeps its name despite 40 percent of the system running above ground.

• 3. From Steam To Spark

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  The unpleasantness came first. Early experiences with steam engines on the Metropolitan Railway, despite ventilation, were grim, and experiments with pneumatic railways failed to win lasting adoption. In 1890, the City and South London Railway became the first electric-traction rapid transit railway, fully underground. Before it opened, the line was to be called the City and South London Subway, which is how the word subway entered railway terminology. The 1893 Liverpool Overhead Railway was designed for electric traction from the very start. The technology spread quickly to Europe, the United States, Argentina, and Canada. Budapest, Chicago, Glasgow, Boston, Buenos Aires, and New York City all converted older lines or purpose-built electric services. In Buenos Aires the first stretch of underground urban railway opened in 1913 as part of Line A, with Vice President Victorino de la Plaza attending the inauguration. Since the 1960s, new systems have arrived across Europe, Asia, and Latin America. In the 21st century, most expansion has moved to Asia, where China alone has almost 60 cities operating, building, or planning a system.

• 4. Digging Down

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  Cut-and-cover is the brute method: city streets are excavated, a tunnel strong enough to carry the road is built in the trench, and the roadway is rebuilt on top. It demands careful relocation of buried power lines, water mains, gas mains, and sewers. According to documentaries from the National Geographic Society, a mislocated water pipeline was one of the causes of the April 1992 explosions in Guadalajara. Bored tunneling instead starts from a vertical shaft, digging horizontally with a tunneling shield and barely disturbing the streets above. London was the first city to use deep tunneling extensively, helped by a thick sedimentary layer of clay that eased both groundwater and excavation. Early machines could not bore tunnels wide enough for ordinary railway equipment, forcing the low, round trains still used on much of the London Underground. That cramped fit is why most of those lines cannot install air conditioning. The deepest system in the world sits in St. Petersburg, Russia, where stable soil begins more than 50 metres down. Only three of its nearly 60 stations are built near ground level, and some tunnels lie as deep as 100 to 120 metres. The very deepest station, Hongyancun in the Chongqing Metro, opened in 2022 at 116 metres.

• 5. Lines And Loads

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  A line's capacity is a simple multiplication: car capacity times train length times service frequency. Heavy systems run six to twelve cars; lighter ones use four or fewer, each car holding 100 to 150 passengers depending on how many stand. Communications-based train control lets the gap between trains, the headway, shrink to as little as 90 seconds, though many systems hold to 120 to recover from delays. Topology decides how those lines cover a city, summarized as I, L, U, S, and O shapes or loops. A study of the 15 largest subway systems found a universal form: a dense core with branches radiating outward. Ring lines, such as the Moscow Metro's Koltsevaya Line and the Beijing Subway's Line 10, connect the radial routes and serve trips that would otherwise cross the congested center. The Chicago L sends most of its lines converging on The Loop, the city's business, financial, and cultural heart. The Shanghai Metro is the world's longest single-operator system by route length, while the New York City Subway leads with 472 stations. By annual ridership, the busiest are the Shanghai Metro, the Tokyo subway system, the Seoul Metro, and the Moscow Metro.

• 6. Reading The System

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  On the Singapore MRT, Changi Airport station carries the code CG2, marking it the second stop on the Changi Airport branch of the East West Line. Interchange stations carry more than one code, so Raffles Place is both NS26 and EW14, the 26th station on the North South Line and the 14th on the East West Line. The Seoul Metro uses mostly numbers, so Sinyongsan on Line 4 is station 429, while City Hall, served by Line 1 and Line 2, holds both 132 and 201. Because Line 2 is a circle line that begins at City Hall, that stop earns the code 201. The Mexico City Metro took a different path entirely, giving each station a unique pictogram. The symbols were meant to make the network map readable by people who could not read, and they have since become an emblem of the system itself. Transit maps follow their own logic, bending geography to clarity. They are usually not geographically accurate, using straight lines, fixed angles, and even spacing to show the topological connections among stations. The standardized GTFS data format now lets outside developers build apps that give riders real-time arrivals and custom updates for the lines they care about.

• 7. Safety Underground

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  Fire is the underground's particular danger. The King's Cross fire in London in November 1987 killed 31 people, and systems are generally built so trains can be evacuated at many points. High platforms, usually over a metre, pose their own risk, since a person who falls onto the tracks struggles to climb back. Platform screen doors are used on some systems to remove that hazard, and they also cut ventilation costs. The first network to fit screen doors onto an already operating system was Hong Kong's MTR, followed by the Singapore MRT. Even so, rapid transit holds a good safety record overall, helped by double track that makes head-on collisions rare and by low speeds that soften rear-end collisions and derailments. The crowds invite other troubles: pickpocketing, baggage theft, and sexual assaults on packed trains, answered with video surveillance, security guards, conductors, and in some countries a specialized transit police. The Beijing Subway, ranked by Worldwide Rapid Transit Data as the world's safest network in 2015, runs airport-style security checkpoints at every station. The systems have also been targets of terrorism, including the 1995 Tokyo subway sarin gas attack and the 2005 bombings on the London Underground.

• 8. The Driverless Turn

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  In the earliest underground railways, a single train needed at least two staff: an attendant to work the doors or gates and a driver at the controls. Powered doors arrived around 1920 and let crews shrink to one. The replacement of the human driver began in the 1960s, with automatic train control and then automatic train operation, which could start a train, bring it to speed, and stop it precisely at the next platform. London's Victoria line, opened in 1968, was the first to use the technology in full. Levels of automation followed in steps. Semi-automatic operation, where a crew member only closes the doors and presses two start buttons, spread to lines like the Bay Area's BART. Driverless operation put a passenger service agent among the riders rather than at the front, as on London's Docklands Light Railway, opened in 1987. Fully unstaffed trains came to newer systems and light metros first. One of the earliest was the VAL, the vehicule automatique leger, used from 1983 on the Lille Metro and later in Toulouse and Turin. The Nuremberg U-Bahn pulled off something no one had: in early 2010 it converted its U2 line to full automation without a single day of service disruption, after running it alongside the driverless U3 from 2008. Singapore's North East MRT line, opened in 2003, was the world's first fully automated underground urban heavy-rail line, a milestone that would soon be matched by the conversion of the Paris Metro's Line 1, completed by 2012.