Caltrain does, on many more trains.

The daily ridership of SP commute in each direction (in other words, a round trip passenger only counts once) was approximately:

1954: 16,000 (peak of SP ridership)
Late 1950s: greadual decline from 16,000-12,000
1960s - early 1970s: 11,000-12,000
By about 1976: 8,000 (the lowest SP ridership)

2008 Caltrain: 36,993 (latest figure I can find. I believe this is each person each way, so it would be about 18,500 using the same convention as the SP statistics above).

There was an abrupt drop off in ridership about 1958 when the Bayshore freeway opened also, as it was declining from the high of 16,000 down to about 12,000 where it remained steady through much of the 1960s.