Light rail transit (LRT) is a form of passenger urban rail transit characterized by a combination of tram and metro features. While its rolling stock is more similar to a traditional tram, it operates at a higher capacity and speed, and often on an exclusive right-of-way. In many cities, light rail transit systems more closely resemble, and are therefore indistinguishable from, traditional underground or at-grade subways and heavy-rail metros.
There is no standard definition, but in the United States (where the terminology was devised in the 1970s from the engineering term light railway), light rail operates primarily along exclusive rights-of-way and uses either individual tramcars or multiple units coupled to form a train that is lower capacity and lower speed than a long heavy-rail passenger train or metro system.
A few light rail networks tend to have characteristics closer to rapid transit or even commuter rail; some of these heavier rapid transit-like systems are referred to as light metros. Other light rail networks are tram-like in nature and partially operate on streets. Light rail systems are found throughout the world, on all inhabited continents. They have been especially popular in recent years due to their lower capital costs and increased reliability compared with heavy rail systems.