Virginia, Georgia, and California are among the states building HOT lanes alongside existing superhighways. They argue that the extra money single drivers kick in for access to the HOT lanes will help pay for other transportation improvements, such as light-rail lines.

But what if so many lone drivers jump at this chance that HOT lanes become just as jammed and slow-moving as regular ones?

American capitalism has the answer. If single-occupancy cars start plugging up the HOT lanes, states plan to just keep raising their tolls. Then, presumably, enough drivers will slink back to the equivalent of the coach section of the road, enabling traffic in the HOT lanes to move briskly again.