Okay. I realize this question is just bait, but I'll answer it anyway, and let my 'Best Answer' percentage slip a little.
Suppose you shut down the busses and commuter trains. Because they have a higher ocupancy rate, they get much higher passenger-miles per gallon than any car (and especially better than a Hummer, if that's what you drive).
So now all those people who took the bus or train have to get where they are going somehow. How do you propose they do that? Walk?
No. They'll find some POS that spews bad stuff into the air and gets terrible fuel mileage (because it's all they can afford), and drive (single occupancy, probably).
That would clog up the roads even more, slowing everybody down, making us all late commuting in stop-and-go traffic, and using even more gas than we do now. (Unless you have a hybrid, you get zero miles per gallon while stopped.)
And that's ignoring the fact that trains run on diesel, and most busses now run on CNG, so they are not competing with cars for fuel.
Professional Automotive Consultant for 20 years, and author of "Car-ma; Why Bad Cars Happen to Good People."