Before I recently retired, I had to do some comparisons of BART ridership density and ridership density in Southern California. It seems that a group made up of academics dominated by Bay Area types had told Business Housing and Transportation that Sou Cal didn't deserve transit oriented development housing bond funds, because we didn't have the transit usage required.

It turns out that Southern California had a 50% higher number of riders per route mile than BART did, even though most of the LA system is light rail. LA has built its limited heavy rail mileage in subway in extremely dense corridors, so it was argued that this skewed the results. However, even the Blue line light rail, through "low density" south LA county had a 30% higher passenger density than BART. This analysis was before the current run up in LA rail ridership of over 25%?

BART is a good system and it should not be torn out, but it is a very expensive commuter rail system, and there are cheaper ways to do commuter rail.