That would only make sense for the most frequented routes but the remaining 80% would be challenging since each person has a unique point A and B across a spraw

That would only make sense for the most frequented routes but the remaining 80% would be challenging since each person has a unique point A and B across a sprawling metropolis. The "last mile" in Los Angeles is a different beast. Each subway route would only improve the commute for less than one percent of the population. A better way would be dedicated bus lanes but it still wouldn't be as efficient as driving due to the amount of transfers you would need.