Because we may not have hammered the point home here's another chart: Cars and planes are pretty inefficient compared to rail.
This graphic, posted by Matt Yglesias yesterday, illustrates a familiar point: Cars and planes are relatively energy inefficient.
But it's also critically important to think about what form of energy these various modes of transportation use, and how flexible they are in that respect. Intercity and commuter trains often run on electricity. That means that as we move to an electricity supply that incorporates more solar and wind power, these forms of transportation will get cleaner in the process. Cars can also be electric, of course, but it will take a while—decades, certainly—before a meaningful portion of the American fleet is off the internal combustion engine. And in terms of where they get energy planes are the worst because, as Yglesias notes, there just aren't low-pollution alternatives to jet fuel.