An interesting comment I received on my hybrid cars post struck me as something to think about. Economists generally advocate the use of tolls and toll lanes to reduce traffic congestion, as opposed to HOV requirements. Often these toll lanes are criticized under the sobriquet of so-called "Lexus Lanes" and it is said to be "unfair" to allow drivers to buy their way out of traffic. But if that is so, why do we allow people to "buy" their way out of traffic and HOV requirements just by purchasing a hybrid car. Moreover, my understanding is that hybrids are more expensive than other cars, made moreso by the high public demand for them (which is one reason for the tax break for them).
Obviously there is thought to be some public benefit from greater hybrid use that might be thought to offset the perception that it is unfair to "buy" one's way into the HOV lane. But the more general observation is that nobody thinks of it as "unfair" to buy your way into the HOV lane by buying a hybrid, yet they do for "Lexus Lanes." In fact, I hadn't thought of it that way until the reader asked me the question.
I suspect that the answer is (extrapolating from the second volume of Hayek's Law, Legislation, and Liberty) "fairness" is a pretty slippery concept once you get beyond small, intimate relations and start trying to apply it to larger legal and policy questions.