This article addresses what we should really be doing in securing our transportation system. We shouldn't worry about spending tons of money and suffering inconvenience to make sure every single aspect of the system is secure. We need to have overlapping layers of defense where each is pretty good but not necessarily perfect. The idea is to deter attacks. If the terrorist need only have sufficient reason to believe that he might be detected as to deter him from trying. You can slow traffic down all over town by setting up speed-trap camera boxes but you only need to have a few cameras. The uncertainty in the perpetrator's mind is the most effective deterrent.

There is no point in trying to protect against or weed out every possible opening for terrorists. That is a traditional approach to transportation security, but it is expensive and demonstrably ineffective. The new strategy should rely instead on layering and interleaving various defensive measures. With layering, each safeguard, even though it may be inadequate by itself, reinforces the others. A layering strategy will not only protect against vulnerabilities in transportation security, it will also deter terrorists by creating uncertainties about the chances of being caught.