As a matter of fact, double deckers have been around for a very long time, in Sydney, Australia. While I was there (late 60s) during a Navy R&R stopover, I rode the line extensively. As I recall, I did not get to ride in one, but I still have a "New South Wales Government Railways" timetable dated 5/5/1968, that shows a picture of one in train, on the cover.

It would be great if BART could do that too, but its tunnels are probably way too tight. The car in the Sydney picture is taller than the rest of the cars. An even somewhat taller BART car would surely scrape the tunnel ceilings.

The Sydney subway system was very similar to BART, in that it served the outlying suburbs with high speed surface lines and used subways at the metro-core. But it did use overhead catenary, not the third rail BART uses. Also, I don't remember ever seeing a grade crossing.

It had a double track subway through downtown, looped around the inner business district. As several lines entered the downtown area, each wyed into the subway loop. While we were there, they were adding additional tracks in the downtown subways loop. On the southwest side, the loop wyed again and merged back in on itself at a very large multi-track Central Station. This is where inter-city trains and express suburban trains could be boarded.

From there, a very high speed six track mainline departed for the suburbs and beyond. It was a fascinating ride, to be running side by side an express train at 90 plus mph, at least until we had to slow for a station stop.

Incidentally, they used a semi-automatic train control system in the suburban territory, not too terribly different than BART's (but I think it was GRS - if memory serves), complete with coded track circuits, cab signaling with few wayside signals, enforced signal compliance, enforced braking, et, al.; except that they did not use an onboard speed servo and automatic departure controls, as BART does; meaning the driver still had to actually drive the train all the time and maintain his assigned schedule himself. If there was an onboard conductor besides the driver, I never saw one.

The Sydney system had all the functions and capability of the PTS systems now proposed - plus some. The new Salt Lake City train control system is very similar, but much more modern, using all microprocessor based components.

The really interesting thing about the Sydney subway, is that with a similar ATC system, similar m.u. cars as BART, and a similar infrastructure, they actually scheduled and routinely achieved the 90 seconds between trains, that BART promised but never managed to deliver. That's 40 trains per hour - per track! I witnessed it myself, each day that I was there.

The Question - if the New South Wales Government Railway could do it with American train control gear, long before BART ever turned a shovel, why the he!! couldn't BART do it?

The Answer - Politicians run BART, not railroad professionals!

OPB