https://theicct.org/planes-trains-and-automobiles-counting-c...
https://www.cato.org/sites/cato.org/files/pubs/pdf/pa-615.pd...
It's talking about 300-500 mile trips (where you might be choosing plane vs train vs car vs bus) and it assumed 2.2 people in the car, and the bus still gets about 3x the efficiency.
I'm not going to waste my time on some Cato nonsense.
That's a good scenario for buses because Grayhound can size buses appropriately and change the frequency. The number for buses within a city is trickier because you have some packed commute buses, and some with 3 passengers at 10 PM.
i live in seattle and joke about always being able to see at least one tesla. and still there are at least as many if not more SUVs than fuel efficient commuter cars.