Only in recent years have transportation engineers and analysts begun to focus on these impacts. More to the point, they are not covered by highway user fees. And that's only part of the true cost of these external impacts. Right now, our highway and airway-based passenger system is ailing. Highway engineers now recognize in most cases that adding lanes to urban interstates won't solve the problem.
Congestion is worse.
Rush hour in Chicago now covers eight hours per day. That's pretty expensive to move your body in your car 15,000 miles a year. Aviation's ability to expand is on a par with the problem of legroom in its passenger seats. The cabin can be reconfigured to add an inch or two, but that's about all. Load factors are at record levels.