History of Trams - Technical Developments

Technical Developments

Modern trams generally use overhead electric cables, from which they draw current through a pantograph, a bow collector (less commonly) or the now-rare trolley pole (the pantograph is most common and used on new tram designs). There are other methods of powering electric trams, sometimes preferred for aesthetic reasons since poles and overhead wires are not required. The old tram systems in London, Manhattan (New York City), and Washington, D.C., used live rails, like those on third-rail electrified railways, but in a conduit underneath the road, from which they drew power through a plough. It was called Conduit current collection. Washington's was the last of these to close, in 1962. Today, no commercial tramway uses this system. More recently, a modern equivalent to the old stud systems has been developed which allows for the safe installation of a third rail on city streets, which is known as surface current collection or ground-level power supply; the main example of this is the new tramway in Bordeaux.

In narrow situations double-track tram lines sometimes reduce to single track, or, to avoid switches, have the tracks interlaced, e.g. in the Leidsestraat in Amsterdam on three short stretches (see map detail); this is known as interlaced or gauntlet track. There is a UK example of interlaced track on the Tramlink, just west of Mitcham Station, where the formation is narrowed by an old landslip causing an obstruction. (See photo in Tramlink entry).

Traditionally trams had high floors, requiring passengers to climb several steps in order to board, but since the 1990s this design has been largely replaced by low-floor trams, or occasionally by high-floor trams with level boarding platforms, as in Manchester's Metrolink and some parts of Cologne's network, which allow passengers in wheelchairs or with perambulators to access vehicles more easily. In some jurisdictions this has even been made mandatory since the 1990s, for example by the HMRI in Britain and the Disability discrimination act in the United Kingdom and other Commonwealth countries.

Historically, the rail gauge has had considerable variations, with narrow gauge common in many early systems. However, most light rail systems are now standard gauge. An important advantage of standard gauge is that standard railway maintenance equipment can be used on it, rather than custom-built machinery. Using standard gauge also allows light rail vehicles to be delivered and relocated conveniently using freight railways and locomotives. Another factor favoring standard gauge is that low-floor vehicles are becoming popular, and there is generally insufficient space for wheelchairs to move between the wheels in a narrow gauge layout.