The things required to increase passengers per bus to the required 3-4 average to beat cars are well known. More frequent service, better route coverage, reduced prices. As these variables move that way, average passenger counts tend to go up. The layout of cities usually does not need to change at all in order to make public transit function well.
I haven't looked at the research recently, but my understanding is that while more frequent service is strongly correlated with higher average passenger counts, the causation seems to be that higher average passenger counts justify increased bus service, and not that increased bus service generally results in higher passenger counts.
Better route coverage likewise.
Reduced prices are complicated. That does increase usage, until the prices drop so far that you attract homeless people who your would-be passengers are scared of. It turns out that making mass transit passengers feel safe is a very important consideration.
More frequent buses tends to have a split effect. The first-order effect is linearly fewer passengers per bus. The second-order effect of people now switching to buses has to be quite strong (and often is) to overcome this direct effect.
I happened to travel from Amsterdam to Boston today (missing King’s Day). There was no chance I wouldn’t take the train to the airport on the Amsterdam end. There was equally no chance that I would take mass transit on the Boston end, despite living in Cambridge.
