US Boeing LRT family Members: Boston, San Francisco (MUNI), Characteristics: Same trains. US Rohr Industries family Members: San Francisco (BART), Washington, Characteristics: Similar, spacious trains with carpets.
The elevated sections of the BART in the East Bay offer gorgeous views of the East Bay hills to the east (see picture: northbound train at Union City) and of downtown San Francisco to the west. You get a particularly good view of the city after you leave West Oakland station but before you go into the transbay tube -- it's quite impressive when it's foggy. Another BART sightseeing tidbit: if you are waiting on the platform of the elevated El Cerrito Del Norte station, you can get a good view of both the Bay Bridge and the Golden Gate Bridge.
BART (newer trains) and MUNI: one-tone beep before the doors close. BART (older trains): "The doors are closing – please stand clear of the doors". This announcement is made at scheduled departure time (20 seconds after the train is stopped or at scheduled departure time, whichever is later) and the doors may actually close quite a bit later without any warning. This is only on trains that are led by an A-cab train (those that have slanted cabs).