The Price Of Homeland Security

John Mueller and Mark G. Stewart have a nice piece drawing attention to the amazing lack of cost-benefit scrutiny involved in homeland security spending:

One question I always have when I go through airport security is exactly how many planes the relevant authorities think al-Qaeda would be blowing up if planes were no better secured than an intercity bus. My experience of intercity bus travel is that there’s absolutely nothing stopping a person from bringing a bomb onto a bus. And yet, over the past ten years exactly zero buses have been exploded by terrorists. A person with the means and inclination to blow up an airplane, who finds himself stymied by tight airline security, could just go blow up a bus instead. But nobody does this. So my baseline assumption is that approximately zero airplane detonations have been prevented by airline security screening, since were screening preventing suicide bombers from blowing up planes we’d see bomb-displacement onto other transportation segments.

Now to be fair to the security side of things, terrorists do seem to have a unique fascination with planes. So maybe it’s not zero explosions we’ve prevented. Maybe it’s… I dunno? One? What do you think? And I’d be interested in what the TSA, FBI, CIA, etc. think the answer is.