Urban rail transit is an all-encompassing term for various types of local rail systems providing passenger service within and around urban or suburban areas. The set of urban rail systems can be roughly subdivided into the following categories, which sometimes overlap because some systems or lines have aspects of multiple types. Types Tram A tram, streetcar, or trolley system is a rail-based transit system that runs mainly or completely along streets (with street running), with a relatively-low capacity and frequent stops. Passengers usually board at the street or curb level, but low-floor trams may allow level boarding. Longer-distance lines are called interurbans or radial railways. Few interurbans remain, most having been upgraded to commuter rail or light rail or abandoned. The term "tram" is used in most parts of the world. In North America, such systems are referred to as "streetcar" or "trolley" systems. In Germany, such systems are called "Straßenbahn", which literally translates as "street train" or "street railway". Updated tram systems have higher passenger capacities than traditional streetcars. Light rail A light rail system is a rail-based transit system that has higher capacity and speed than a tram, usually by operating in an exclusive right-of-way separated from automobile traffic, but it is not, unlike rapid transit, fully grade-separated from other traffic. Light rail also generally operates with multiple-units trains, rather than single tramcars. It emerged as an evolution of trams/streetcars. Light rail systems vary significantly in terms of speed and capacity and range from slightly-improved tram systems to systems that are essentially rapid transit but with some level crossings. The term "light rail" is the most common term, but German systems are called "Stadtbahn", which translates to "city railway". Rapid transit A rapid transit system is a railway, usually in an urban area, with high passenger capacities and frequency of service and (usually) full grade separation from other traffic, including other rail traffic. It is often known as "heavy rail" to distinguish it from light rail and from bus rapid transit. In most parts of the world, such systems are known as a "metro", short for "metropolitan", which is itself short for "Metropolitan Railway", the first such system in the world. The term "subway" is used in many American systems, as well as in Glasgow and in Toronto. The system in London is named the "Underground" and is commonly nicknamed the "tube". Systems in Germany are called "U-Bahn",