“Cable cars” were once a common form of public transportation in many American cities.  Cars were pulled along the track by an endless-loop steel cable, positioned in channel beneath the street.  The cars moved by “gripping’ the cable and stopped by releasing it.  Cable cars were a big improvement over horse-drawn streetcars, especially on hilly routes that were too steep for horses to negotiate safely.  Los Angeles got its first cable cars in 1885 with the opening of the 2nd Street Cable Railway.  Most cable railways eventually gave way to electric trolley cars and ultimately to buses.  However, the very hilly city of San Francisco continues to operate several of its iconic cable car lines as vital components of its transit system.  Car No. 21 is an example of the double-ended “California Car” – this type car has “grips” at both ends, allowing it to operate in either direction on the route, without having to be ‘turned around’ at the end of the line.