I live in LA and travel to the Bay for work frequently. I can walk to a Metro station from my house in Highland Park in 10 minutes and be at Union Station in 13 minutes. If I could spend 3 hours on the train to SF from Union instead of driving to Burbank, arriving an hour before my flight, and then spending an hour on a plane, I would do it every time.
You can't make a city transit and walking friendly by grafting rail infrastructure over a car-based design. You need to allow development on narrower streets without minimum parking requirements on every lot and you need more population density.
You'd have to actually change the rules and overcome the NIMBYs. Some problems can't be solved with cash.
Pretty much this, if its sub-5 story slum (aka most US cities & nearly all suburbs) overlaying rail is a bandaid. The city was built wrong in the first place, and needs to gain density, rail can keep a dense city economically viable by providing reliable, rapid transit. There is no good transit solution for suburban sprawl.