Operation

Rapid transit is used in cities, agglomerations, and metropolitan areas to transport large numbers of people often short distances at high frequency. The extent of the rapid transit system varies greatly between cities, with several transport strategies.

Some systems may extend only to the limits of the inner city, or to its inner ring of suburbs with trains making frequent station stops. The outer suburbs may then be reached by a separate commuter rail network where more widely spaced stations allow higher speeds. In some cases the differences between urban rapid transit and suburban systems are not clear.

Rapid transit systems may be supplemented by other systems such as trolleybuses, regular buses, trams, or commuter rail. This combination of transit modes serves to offset certain limitations of rapid transit such as limited stops and long walking distances between outside access points. Bus or tram feeder systems transport people to rapid transit stops.

Linesedit

Each rapid transit system consists of one or more lines, or circuits. Each line is serviced by at least one specific route with trains stopping at all or some of the line's stations. Most systems operate several routes, and distinguish them by colors, names, numbering, or a combination thereof. Some lines may share track with each other for a portion of their route or operate solely on their own right-of-way. Often a line running through the city center forks into two or more branches in the suburbs, allowing a higher service frequency in the center. This arrangement is used by many systems, such as the Copenhagen Metro, the Milan Metro, the Oslo Metro and the New York City Subway.

Alternatively, there may be a single central terminal (often shared with the central railway station), or multiple interchange stations between lines in the city center, for instance in the Prague Metro. The London Underground and Paris Métro are densely built systems with a matrix of crisscrossing lines throughout the cities. The Chicago 'L' has most of its lines converging on The Loop, the main business, financial, and cultural area. Some systems have a circular line around the city center connecting to radially arranged outward lines, such as the Moscow Metro's Koltsevaya Line and Beijing Subway's Line 10.

The capacity of a line is obtained by multiplying the car capacity, the train length, and the service frequency. Heavy rapid transit trains might have six to twelve cars, while lighter systems may use four or fewer. Cars have a capacity of 100 to 150 passengers, varying with the seated to standing ratio—more standing gives higher capacity. The minimum time interval between trains is shorter for rapid transit than for mainline railways owing to the use of Communications based train control: the minimum headway can reach 90 seconds, but many systems typically use 120 seconds to allow for recovery from delays. Typical capacity lines allow 1,200 people per train, giving 36,000 people per hour. The highest attained capacity is 80,000 people per hour by the MTR Corporation in Hong Kong.

Network topologiesedit

Rapid transit topologies are determined by a large number of factors, including geographical barriers, existing or expected travel patterns, construction costs, politics, and historical constraints. A transit system is expected to serve an area of land with a set of lines, which consist of shapes summarized as "I", "U", "S", and "O" shapes or loops. Geographical barriers may cause chokepoints where transit lines must converge (for example, to cross a body of water), which are potential congestion sites but also offer an opportunity for transfers between lines. Ring lines provide good coverage, connect between the radial lines and serve tangential trips that would otherwise need to cross the typically congested core of the network. A rough grid pattern can offer a wide variety of routes while still maintaining reasonable speed and frequency of service. A study of the 15 world largest subway systems suggested a universal shape composed of a dense core with branches radiating from it.

Passenger informationedit

Rapid transit operators have often built up strong brands, often focused on easy recognition—to allow quick identification even in the vast array of signage found in large cities—combined with the desire to communicate speed, safety, and authority. In many cities, there is a single corporate image for the entire transit authority, but the rapid transit uses its own logo that fits into the profile.

A transit map is a topological map or schematic diagram used to show the routes and stations in a public transport system. The main components are color-coded lines to indicate each line or service, with named icons to indicate stations. Maps may show only rapid transit or also include other modes of public transport. Transit maps can be found in transit vehicles, on platforms, elsewhere in stations, and in printed timetables. Maps help users understand the interconnections between different parts of the system; for example, they show the interchange stations where passengers can transfer between lines. Unlike conventional maps, transit maps are usually not geographically accurate, but emphasize the topological connections among the different stations. The graphic presentation may use straight lines and fixed angles, and often a fixed minimum distance between stations, to simplify the display of the transit network. Often this has the effect of compressing the distance between stations in the outer area of the system, and expanding distances between those close to the center.

Some systems assign unique alphanumeric codes to each of their stations to help commuters identify them, which briefly encodes information about the line it is on, and its position on the line. For example, on the Singapore MRT, Changi Airport MRT station has the alphanumeric code CG2, indicating its position as the 2nd station on the Changi Airport branch of the East West Line. Interchange stations would have at least two codes, for example, Raffles Place MRT station has two codes, NS26 and EW14, the 26th station on the North South Line and the 14th station on the East West Line. Seoul Metro is another example that utilizes a code for its stations. But unlike that of Singapore's MRT, it's mostly numbers. Based on the line number, for example Sinyongsan station, coded as station 429. As it is on Line 4, the first number of the station code is 4. The last 2 numbers will be the station number on that line. Interchange stations can have multiple codes. Like City Hall station in Seoul which is served by Line 1 and Line 2. It has a code of 132 and 201 respectively. The Line 2 is a circle line and the first stop is City Hall, therefore, City Hall has the station code of 201. For lines without a number like Bundang line it will have an alphanumeric code. Lines without a number that are operated by KORAIL will start with the letter 'K'.

With widespread use of the Internet and cell phones globally, transit operators now use these technologies to present information to their users. In addition to online maps and timetables, some transit operators now offer real-time information which allows passengers to know when the next vehicle will arrive, and expected travel times. The standardized GTFS data format for transit information allows many third-party software developers to produce web and smartphone app programs which give passengers customized updates regarding specific transit lines and stations of interest.

Safety and securityedit

Compared to other modes of transport, rapid transit has a good safety record, with few accidents. Rail transport is subject to strict safety regulations, with requirements for procedure and maintenance to minimize risk. Head-on collisions are rare due to use of double track, and low operating speeds reduce the occurrence and severity of rear-end collisions and derailments. Fire is more of a danger underground, such as the King's Cross fire in London in November 1987, which killed 31 people. Systems are generally built to allow evacuation of trains at many places throughout the system.

High platforms (usually over 1 meter / 3 feet) are a safety risk, as people falling onto the tracks have trouble climbing back. Platform screen doors are used on some systems to eliminate this danger.

Rapid transit facilities are public spaces and may suffer from security problems: petty crimes, such as pickpocketing and baggage theft, and more serious violent crimes, as well as sexual assaults on tightly packed trains and platforms. Security measures include video surveillance, security guards, and conductors. In some countries a specialized transit police may be established. These security measures are normally integrated with measures to protect revenue by checking that passengers are not travelling without paying. Some subway systems, such as the Beijing Subway, which is ranked by Worldwide Rapid Transit Data as the "World's Safest Rapid Transit Network" in 2015, incorporate airport-style security checkpoints at every station. Rapid transit systems have been subject to terrorism with many casualties, such as the 1995 Tokyo subway sarin gas attack and the 2005 "7/7" terrorist bombings on the London Underground.

Added featuresedit

Some rapid transport trains have extra features such as wall sockets and internet connectivity. For example, the Hong Kong Mass Transit Railway (MTR) provides mobile data connection in the tunnels for selected service providers.