Don't let the name fool you, these are in fact
street cars, with a modern touch. Light rail vehicles are called such, to differentiate them from
heavy rail trains, also known in many cities as
subways, or
metro. This can get confusing, as many lightrail lines run into tunnels, and are thus also subway lines.
Some cities, such as Pittsburgh, PA, never got rid off their streetcars, and simply modernized their existing system. Others, like Baltimore, converted underutilized railroad tracks into a rapid transit system.