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In the United States, "light railway" generally refers to an urban or interurban rail system, which historically would correspond to a streetcar network. The distinct term light rail was introduced in the 1970s to describe a form of urban rail public transportation that has a lower capacity and lower speed than a heavy rail or metro system, but which generally operates in exclusive rights-of-way, in contrast with streetcar systems which operate in shared road traffic with automobiles. Urban sprawl combined with higher fuel prices has caused an increase in popularity of these light rail systems in recent decades.