While stuck in traffic west of Portland on US 26, which I sometimes think of affectionately as the Sunset Walkway, another reason to limit SUVs occurred to me that has nothing to do with their poor gas mileage.
A freeway can hold only so many cars in each lane-mile. The upper limit can be calculated based on the average car length and the distance between cars. If cars get shorter, then the freeway could hold more cars. Let's tax cars the same way we tax boats: the longer the car, the more we pay for the license plates. And why not? If you're using 17 feet of the road and I'm using only 12 feet, then you're taking up more space than I am, and you should pay more for the privilege. And if the SUV drivers switch to shorter cars, then the freeway capacity goes up substantially, without capital investment. Make shorter cheaper.