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What exactly is a tram? What is the difference between trams and light rail? What distinguishes trams and light rail from conventional railways?

Trams and light rail are forms of urban public transport; with a handful of exceptions, tramways and light rail systems across the world are almost exclusively passenger-carrying operations. There is no hard and fast definition of what constitutes 'Light Rail' or what the difference is between light rail and trams, and there are different opinions on what exactly the terms mean, but this page should give you an idea.

Trams

photo of Blackpool tram on the Promenade

A tram, usually known in North America as a 'streetcar', 'trolleycar' or 'trolley', is a vehicle which runs on fixed rails and is designed to travel on streets, sharing roadspace with other traffic and pedestrians. Most tram systems also include at least some off-street running, either along the central reservation of roads (what would be called the 'median strip' in the US) or on fully segregated alignments. Such section of route can be called 'reserved rights of way'. Some tram systems run mostly on reserved tracks, with only short stretchs of on-street running. Many of the tram systems in the UK utilise former railway alignments, or share what were previously railway-only alignments with heavy rail services.

The tracks that a tram runs on are called a tramway; the system itself can be called a tramway system.

First generation tramways

Horse-drawn tramways were first introduced at the beginning of the 19th Century. The first electric tramway began operation in Germany in 1881, and existing horse-drawn tramways were progressively converted to electric operation. With the emergence of motorbuses and trolleybuses (also known as trackless trolleys) which run on rubber tyres without needing rails, tramways started to fall out of favour. In many countries (the UK and the US for example), many tram systems were abandonded in favour of these alternative forms of mass transit; the rising popularity of private cars also had a detrimental effect on the viability of tramways. In Britain, by the end of 1962 all but one tramway system (Blackpool) had closed. In North America, all but a tiny handful of tramways had closed by the mid 1960s. Many systems remained open in continental Europe, and have been progressively modernised.

Light rail

photo of a Metrolink tram on reserved track

The term 'light rail' is used to describe railway operations using smaller vehicles which have a lower capacity and lower speed than conventional railways; light rail infrastructure is designed to be cheaper to build and maintain. Light rail is an intermediate transport mode, catering for short intra- and inter-urban journeys—stops are generally closer together than commuter railways but further apart than local bus routes.

Because of the nature of the technology used, light rail systems are often subject to less stringent operational regulation than conventional railways, which leads to greater opearational flexibility. For instance, 'heavy rail' systems will normally be required to operate block signalling systems which create an absolute limit on track capacity—maximum headway. By contrast many light rail systems, by virtue of their slower speeds, lighter vehicle construction and shorter braking distances, are able to operate on line-of-sight, allowing vehicles to pull up right behind one another, meaning there is virtually no limit to track capacity.

Light rail systems typically feature high-frequency services, removing the need for anything more than the most basic public timetables. Stops are often less substantial than conventional railway stations, and are generally unstaffed; they can range from converted former railway stations to little more than a bus stop.

A common feature of many light rail systems, particularly those which feature street running, is that they are more integrated into the urban environment than conventional railways. In particular, stops can be designed to be a part of the communities they serve rather than being physically seperated from them. This design approach impacts on public awareness and passenger perception and can make people more likely to consider travelling on them.

Light rail systems almost universally feature electric power, although there are a very small number of diesel light rail vehicles. Tram-train, a modern concept which has been trialled in Germany, features hybrid vehicles which travel into a city on main line railway tracks, under diesel power if necessary, before switching to tram tracks and electric power for the journey through the city centre.

Difference between trams and light rail

photo of a Nottingham Express Transit tram running on-street

Light rail is a relatively modern term, and can be applied to quite a broad spectrum of systems. Virtually every tram systems can be considered as light rail, but only those light rail systems which feature street running can be called trams. It could be said that as light rail is a modern term, only modern systems could be called light rail; however, older tramways still incorporate many of the features of modern light rail systems, and many have also been progressively modernised so that they are vey similar to more recently constructed systems.

Metro

Some light rail systems are referred to as 'Metros'. 'Metro' is a term which can be used to describe a high-frequency inter- or intra-urban railway system, which is entirely or largely seperate from other main line railway operations. Metro systems often, but not always, feature sections of underground railway and underground stations.

Metros can use either conventional heavy rail technology (heavy metro) or modern light rail technology (light metro). An example in Britain of heavy metro would be the London Underground; examples in Britain of light metro are the Tyne and Wear Metro and the Docklands Light Railway.

diagram illustrating the tram to light rail to metro spectrum
 

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