While trains are touted as very efficient modes of transportation, and generally beloved by nerds, I'm skeptical, largely because train tracks are so under-utilized.
Train tracks take up as much space as many multi-lane highways. On highways, dozens of cars go by every minute. But a train car only passes through at best a few times an hour. I suspect that if you took one mile of train track and one mile of a highway with the same overall footprint, far more people/goods will move through the highway-mile every hour than the train-mile.
Don't have data to back this up, just a hunch. But if it's true, then even though trains are far more energy efficient than cars, they're likely far less real-estate efficient.
(Also, I do suspect that this is not always true. A heavily trafficked tunnel in/out of Manhattan's Penn Station is probably more efficient real-estate wise than an equivalent tunnel. But that's a very extreme case with super high densities).