Banning Cars from Boulevards

There was an article in the Los Angeles Times on banning cars from Wilshire Avenue and bringing the Subway to the surface. There are tons of cross streets meaning that there would have to be a lot of over or underpasses if it was going to be grade separated. Maybe this can be achieved by tunneling under the major intersections and not allowing cross traffic on the smaller ones. Although everyone would be pretty mad about the construction. I really like the idea of subways though. Mostly because they can go in straighter lines and you won't have the ugly under and overpass issues. They also integrate into the landscape better since people don't have to cross streets. The New York Subways were an investment made over 100 years ago, why can't LA make that investment for the lifetime of that city?