The surface operation of the BOT was a costly operation, resulting from the various equipment that was required, including trolley cars, trolley coaches, gasoline and diesel buses, of which many were obsolete and in need of replacement.
12.
In San Francisco, these vehicles are also known as " trolley coaches " ( a term that was the most common name for the mode in the United States in the middle decades of the 20th Century ).
13.
By this time, and continuing until the 1970s, the most common term in North American English for this mode of transportation was " trolley coach ", but in Philadelphia the mode has always been commonly called the trackless trolley.
14.
All told, Twin Coach manufactured only 670 " trolley coaches " as such vehicles were commonly called at the time but sold them to 16 different cities ( all in the U . S . ), which equates to around one-third of all of the trolley bus systems ever to exist in the United States.
