That’s a very wrong conclusion to draw from the study. If median income of someone riding the bart is higher than someone driving, it could also mean that they drive because it is cheaper to do so. If you make it free, they would probably ride BART too, making it more accessible and equitable.

The study was more in depth than that. It found that BART goes to more places that wealthy people go (financial district, SOMA, etc) than where poorer people need to go.

That makes perfect sense. Poor people are attracted to cheaper real estate (residential and commercially). Real estate is cheaper because it is less accessible and convenient.

One area is concentrated and the other is decentralized.

Please forgive me for the ignorance, but is there some significance of “under the bay bridge” for this study, or did they just pick it arbitrarily? It seems like picking a point arbitrarily like that could introduce some skews.

I'm pretty sure it's just being used as a turn of phrase here. Under the bridge means commuters are riding BART, over the bridge means they're driving.

So, force the rich people to use the bridge, and increase commute times for everyone?

Seems like a much better plan than synchronizing and expanding the train networks so they cover more neighborhoods in all parts of the bay (except Marin, of course…)

I don't care it should be free.

Yes, let's ignore all data saying that it being free would make everything worse and not address any of your concerns about the environment or helping poor people.