While I wholeheartedly agree that the Department of Transportation should be required to estimate the costs and benefits of new security policies, I don’t agree with the above analogy. Certain security measures may not be worth their costs, but if we reduced airport security to the levels seen on buses, would-be terrorists would have strong incentives to carry out an attack.

First, an airplane can be used as a weapon in a way a bus can’t. If a terrorist were to hijack a bus and attempt to drive it into a major building, there are a number of ways that law enforcement can stop the attack from succeeding. In many situations, police will find out quickly about such an incident and can respond in kind. They can set-up blockades, shut down parts of the city and track the vehicle easily. On an airplane though, law enforcement have few methods to respond. They cannot simply shoot the plane down and sacrifice the Americans on it. There is no way to set up a blockade.

Second, bus riders can text or phone friends to alert the authorities if the attack is not clear. In the air however, passengers cannot easily communicate with friends and family on the ground. Notifying the authorities of the attack is much more difficult from the sky than from the ground.

Third, a terrorist attack from a plane has the potential to be much more deadly than one on a bus.  At the very least, there are more people on a plane than on a bus. But terrorists can also inflict significantly more damage crashing a plane into a tall building or a secure location than they can running a bus into a similar target. Planes can crash into locations that cars and buses cannot even travel to (for example, the White House). This makes a hijacked plane much more dangerous than a hijacked bus.

Fourth, an attack from the sky is more emotionally damaging than one from the ground. We are unfortunately becoming more used to mass shootings and other threats on the ground. Part of the reason that 9/11 scared Americans so much was that it was the first time that we were attacked from the sky. That’s part of what makes drones so scary for Middle Easterners. You can’t see them and don’t know that they’re there – but they can strike at any moment. Before 9/11, we didn’t think twice about such a threat. Afterwards, we are now all alert and aware that we are not immune. A bus bombing would terrify us, but we can see a bus coming from a distance and can attempt to avoid it if it’s heading right at you. If you are so scarred from such an event, you can avoid buses for the rest of your life. You can’t avoid a plane striking your home or office out of nowhere. You don’t see it coming until it’s too late and there’s no way to fully protect yourself. That fear sticks with you for the rest of your life.

For all those reasons, terrorists have greater incentives to hijack a plane than a bus. That’s why Yglesias’s analogy doesn’t work. Now, there are some TSA policies that almost certainly have costs greater than their benefits (banning pocket knives) and Yglesias is right that we need agencies to conduct cost-benefit analyses more often. With specific estimates of the costs and benefits of a proposed policy, politicians will have more confidence in supporting less security. After all, no politician wants to risk advocating for reduced security and then face voters if a terrorist attack does happen. This biases the entire system towards excessive security. At least with a cost-benefit analysis, Congressmen will have specific statistics to show their constituents for why they voted for such a policy. If that alone can reduce the bias in the system, it’s worth a shot.