> The trouble with this graph is that it assumes the buses/trains are full. It obviously doesn't apply to a bus with one passenger on it, which takes up even more space than a car.

IMHO it's a bit moot to delve into extremes. Average car occupancy is around 1.5 passengers. I'd bet that such number is far from average for average bus/train/tram/metro. I also probably won't make a mistake stating that "Average car" in USA is either a very big SUV or even bigger "truck" (which probably has a footprint as half of a bus). You also need to park your car somewhere at the destination.

I also thought that there will be reply like yours, though you answered your own problem:

> To fix this the thing you need before mass transit (by several years) is zoning rules that allow higher density construction in a higher percentage of the land area where people live and work.

Of course you don't want to build trams and all in low density (and low population) areas and my comment didn't apply for such case. You must have density as well as mixed use zones. I am not from USA and seemingly prevalent single use zoning[1] is very foreign to me. It all comes down to efficient urbant planning.

[1] correct me if I am wrong on this.