Incompatible guage guaranteed no use of any existing trackage. I have always believed this was related to the early dream of BART circling the Bay. SP was adamant about abolishing commuter service and not at all interested in having 'gummint' interference or takeover (what a difference a generation makes!) At the time the corporate link between SP Co and Bechtel (member of the managing consortium responsible for BART engineering decisions) was very close. S. D. Sr. Chairman of the Board, S. D. Jr a member. source SP Co annual report circa 1962 approximately when the guage decision was made. Mr. Robl is correct as to inherent and recurring extra cost; sadly the control system snafu and badly managed car fleet procurement were even more damaging. We got a marginally adequate $792 million system(the original price advertised) unfortunately we paid over 2 billion for it and three and a half decades later still do not have the level of service promised in the propaganda (90 sec headways in rush).