A streetcar named light rail

Light rail systems, which are descended from streetcars and interurban electric railroads, are coming into favor in North America. They differ from their progenitors in three main areas: the degree of separation between their tracks and other traffic, vehicle technology, and operating practices. Whereas streetcars intermingled with other street traffic throughout most of their routes, light rail vehicles (LRVs) typically run along exclusive or semiexclusive rights-of-way, and they can make use of several different right-of-way types. Modern light rail transit (LRT) systems use articulated vehicles, which are much more cost-effective than shorter rigid cars because they can carry more passengers and are operated by just one person. Consisting of two sections joined at a single truck, or bogie, articulated cars can be much longer yet still negotiate sharp curves. The vehicles in modern LRT systems are operated in much the same way as were their streetcar ancestors; an operator, in line-of-sight operation, manually controls the vehicles. In some systems, to increase efficiency, traffic signals are preempted by the LRV; when an LRV approaches a grade crossing, sensors in the track detect it and give it a green light, forcing the intersecting automotive traffic to stop. Existing and planned systems are noted.<>