Passenger rail terminology
[1] Originally, the term rapid transit was used in the 1800s to describe new forms of quick urban public transportation that had a right-of-way separated from street traffic.
Rail systems with specific construction issues operating on a segregated guideway (e.g. monorail, rack railways) are also treated as Metros as long as they are designated as part of the urban public transport network.
Naming practices often select one type of placement in a system where several are used; there are many subways with above-ground components, and on the other hand, the Vancouver SkyTrain and Chicago "L" include underground sections.
Sometimes the term is qualified, such as in Philadelphia, where trolleys operate in an actual subway for part of their route and on city streets for the remainder.
Until March 2019, Seattle had a downtown bus subway in which diesel-electric hybrid buses and light rail trains operated in a shared tunnel.
[citation needed] Subway, outside the US, and especially in Europe, often refers to an underground pedestrian passageway linking large road interconnections that are often too difficult or dangerous to cross at ground level.
[7] However, strictly speaking, it should only refer to those deep lines which run in bored circular tunnels as opposed to those constructed near to the surface by 'cut-and-cover' methods.
In Switzerland, where there is only one underground railway system in Lausanne, the term metro is generally used, due to the influence from the French language.
In North America, the American Public Transportation Association defines a heavy-rail system as an electric railway with the capacity to handle a heavy volume of traffic.
It is characterized by high-speed, passenger rail cars running in separate rights-of-way from which all other vehicular and foot traffic are excluded.
Tram is a British word, cognate with the Low German traam, and the Dutch trame, meaning the "shafts of a wheelbarrow".
Other common North American English meanings of the term tram include aerial cable cars and short-distance, rubber-tired people-movers (such as at certain airports).
[citation needed] Specific terms for some historically important tram technologies include horsecar, heritage streetcar, and cable car.
A few systems such as people movers and personal rapid transit could be considered as even "lighter", at least in terms of how many passengers are moved per vehicle and the speed at which they travel.
Parry People Mover which is grade-separated, low passenger capacity (maximum 35 standing) powered by LPG with no overhead lines, has been described as ultra light rail.
[19][20][21][22] The proposed Coventry Very Light Rail which is at-grade, low passenger capacity (60-70 people), battery powered so no overhead lines also falls into this category.
A few interurbans like Philadelphia and Western Railroad adapted to high speeds with double-track, absolute block signalling and without grade crossings.
Some interurban trains may operate from where suburban lines end, such as Southern Higlands services between Campbelltown and Goulburn, or between Ipswich and Rosewood.
Examples include the former BR's Regional Railways, France's TER (Transport express régional) and Germany's DB Regio services.
The term "people mover" has become generic for the type of system, which may use technologies such as monorail, duorail, automated guideway transit or maglev.
Monorail means a system of guided transit vehicles operating on or suspended from a single rail, beam, or tube.
These services are provided after improvements to the conventional rail infrastructure in order to support trains that can operate safely at higher speeds.
Track radius will often be the ultimate limiting factor in a train's speed, with passenger discomfort often more imminent than the danger of derailment.
Depending on design speed, banking, and the forces deemed acceptable to the passengers, curves often exceed a 5 kilometer radius.
Tilting trains have been developed for achieving greater comfort for passengers, so higher speeds are possible on curvy tracks.
Although a few exceptions exist, zero grade crossings is a policy adopted almost worldwide, with advanced switches utilizing very low entry and frog angles.
It is important to note that the current world record for rail vehicles is held by the TGV V150 set on 15 April 2007 at 574.8 km/h (357.2 mph), and conventional trains may indeed eventually reach into ultra high-speeds.
Regardless of technological parameters, the track for such a train and anything faster would more than likely require turn radii of significantly higher proportions than current dimensions, essentially preventing anything but a direct line between terminals.
Depending on the aerodynamic design of the vehicle and various ambient atmospheric conditions, a train would begin to exhibit transonic airflow in the vicinity of Mach 0.8 (988 km/h) and higher.
This is because the Prandtl-Glauert singularity would cause catastrophic damage to the vehicle as the sound waves reflected off of the ground, potentially blasting the train into the air.
