After teaching a class last night during which we discussed substitutes, I realized that the recent eruption by Eyjafjallajökull, while sad for all involved, presents a good teaching example. The exogenous elimination of air travel led predictably to a scramble for substitutes. Eurostar ran out of capacity and quadrupled their ticket prices; a black market also naturally emerged. Meanwhile bus companies, facing more rivals than Eurostar, kept the same price but temporarily boosted the number of buses they ran. Taxi drivers cashed in on customers including John Cleese who paid $5000 for his ride. I couldn’t help but reflect upon our trip to Japan last month, where we enjoyed riding on the Shinkansen bullet train. The ride was quick and smooth, there were no long waits at security lines and elaborate rituals at airports, legspace was ample, and our electronic equipment did not have to be switched off during takeoff and landing. Air travel is overrated.