Near my parents' home, there's an intersection of a 18 lanes (!) of highway + access road crossing over a 9-lane surface street. I just don't know how you grow that any further, without the prohibitively expensive option of more vertical stacking.

I've always thought of our current car-based transportation system to be amazingly inefficient when measured in energy consumption per passenger and travel time. But I'm noticing it's also extremely greedy with land use.