HEAVY RAIL

The term 'heavy rail' is often used for regular railways, to distinguish from systems such as trams, light rail, medium capacity system, and metro.
Heavy rail typically refers to the standard inter-city rail network, which is built to be robust enough for heavy and high-speed trains, including freight trains, and long distance and high speed passenger trains. For these reasons, curves and slopes are gentle. Heavy rail is almost always built on its own dedicated right-of-way and is separate from road traffic.
This distinguishes it from light rail which is built to lightweight construction including a steeper ruling gradient, suitable to lightweight trains or trams, and usually, but not always, intended for passenger traffic only, usually in urban and suburban areas.
In the United States, the term is used as the general term for metro systems (underground systems and systems that are not running below the ground but are similar to underground systems in other respects); when the term is used in this way, it should be distinguished from commuter rail and inter-city rail services, which cover longer distances and may share tracks with freight trains. This usage is seldom found outside the United States; in Britain, the term is instead used to differentiate the standard railway network, particularly the urban and suburban services offered by various National Rail companies, from local rail transit systems such as the London Underground and its counterparts.