Electric trolleys on rails, also known as streetcars, lend a sense of permanence to a neighborhood that helps create strong economic corridors. Trolley systems are typically more efficient and have a higher carrying capacity than buses, making them ideal for transit in small established districts, particularly downtowns. The high visibility of trolleys and their tracks allows for greater simplicity in using the system, especially benefiting visitors and tourists, as the streetcars in San Francisco exemplify. The use of electricity rather than petroleum based fuel sources reduces pollution in dense areas. Streetcars also have a much longer life than buses systems, and help decrease the number of cars on a road. The initial cost of trolleys on rail will be higher, but it can be a long-term, attractive method of public transportation.