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Horse tramcar

But reached this point, the desire of improving the traction emerged, being adopted that which was then available: mechanical traction by steam. And as usual, it was England which made the first experiments, but not with small locomotives built on purpose, but with steam engines installed either in small carriages which towed the cars or in the very cars. Despite far from perfect, steam tramcars had a great development, to the point that in 1895 about 5000 cars existed in New York, operating in a railway network of 1360 kilometers in length.

Old American tramcar
One of the first models of American tramcars.
Old American elevated train
A project by James Swett from 1853 for an elevated line. Curiously, the locomotive should not tow the passenger car, but carry it in a hanging position.

There were as well experiments with traction by compressed air; in 1827 British engineer George Medhurst wrote an essay proposing such method for transporting passengers. The system consisted of a small car which would be literally suctioned by a pneumatic pump along a duct. In 1830 another British engineer, Samuel Clegg, solved the various inconvenients derived from the necessity of keeping the duct hermetically closed, by adding a longitudinal valve. This allowed to establish in the outskirts of London a section of which was called the "atmospheric railway".

In France these "atmospheric" lines had success as well, despite the inconveniences: the machines required to move the vehicles had a considerable size and they had to be kept in operation constantly, despite the travels being quite unfrequent, with the consequent high costs in maintenance. However, this locomotion system found an economic utilization for transporting mail, from the offices in the periphery to the central offices, through underground tubes. It seems that the speed achieved with this system induced to establish underground lines for transporting passengers as well; the first attempt of this kind was effectuated in New York in 1872.

New York metropolitan subway, 1872
A metropolitan subway of circular cross-section that was experimented in New York in 1872.

But it was the adoption of electric traction in 1883 what brought true progress in the field of metropolitan public transport; in New York the line "Elevated" was provided with a third rail for supplying the energy to the tramcars. But the definitive system would be that introduced by Frank Julian Sprague in 1885, who suppressed the electrified rail which produced shocks in pedestrians and animals alike, replacing it by overhead lines and trolleys which took the electricity from them. Milan was the first Italian city in which tramcars were installed, in 1893.

Milan metropolitan subway, 1960
The subway transport was inaugurated in Milan in November 1964. In 2015, with a total length of 92 kilometers, this network had more than doubled the length of its counterpart in Rome.

Circa 1975 the metropolitan subways had these lengths (in kilometers) in the following cities: New York (381); London (348); Chicago (258.6); Paris (189); Berlin (94.1); Moscow (77); Hamburg (74.3); Tokyo (59.9); Mexico (42.2); Philadelphia (42); Stockholm (40.4); Madrid (39.5); Boston (37.3); Buenos Aires (30.7); Vienna (26.7); Athens (25.6); Osaka (19.9); Barcelona (17.7); Leningrad (14.5); Rome (11); Glasgow (10.5); Toronto (10.4); Lisbon (7.3); Rotterdam (6); Kiev (5.9); Budapest (3.7).

Circa 2015 the same metropolitan subways had these lengths: London (408); New York (336); Tokyo (338.7); Madrid (324); Moscow (317.5); Mexico (225.9); Paris (219.9); Chicago (170.8); Berlin (151.7); Osaka (129.9); Barcelona (123); Saint Petersburg (113.2); Stockholm (105.7); Hamburg (104); Athens (83.3); Vienna (78.4); Rotterdam (78.3); Toronto (68.3); Kiev (67.6); Philadelphia (63.5); Buenos Aires (58.8); Boston (51); Lisbon (45.5); Rome (40.4); Budapest (31.4); Glasgow (10.4).

The future of railway design

In the largest cities the metropolitan subway intersect many lines at different levels, but the continuous growing of these metropolis would soon render as insufficient this means of transportation as well. Thus, new and audacious solutions had to be investigated. The inventive of engineers brought ideas that not always seemed very practical or realizable; for example, aerial lines of small cabins hanging from funiculars supported by pillars. However, a similar method has been eventually put into practice in recent years, and it is yet to be seen if it will reach a more than symbollic implantation.

To this day the implantation of the monorail has enjoyed a relative success. This system is an updated version of the classic railcar, a small train which has no wheels (at least in a traditional sense) and is coupled to a single rail along which it can move, either at regular speeds, by means of small wheels which traction on the rail, or at very high speeds, when the train is kept afloat on an "air cushion" to reduce friction to the minimum possible. In the first case, the train is impulsed by conventional electric motors (rotatory type), while in the second case the train is impulsed by linear induction motors, a system which is referred as "magnetic levitation".

Vintage monorail design

As linear induction motors do not require physical contact between the vehicle and the track, they were used in the first experiments of high-speed trains, in the 1960s. Experimental projects that were devised in that time include the aerotrain and the tubular train. The first one was a type of air-cushion monorail which was impulsed by a turbo-propeller engine, and which should be capable of reaching speeds of up to 400 kilometers/hour. In the second one, which requires an air cushion as well, the air absorbed by a turbine should be able to impulse the train at speeds above 800 kilometers/hour.