School buses and drivers are idle following a "credible" threat of danger at schools in Los Angeles on Tuesday. (EPA/Paul Buck)

The Los Angeles Times is reporting that a 17-year-old student was fatally struck by a car Tuesday morning after all city schools were closed following a '"credible threat" of violence. The decision to shut down the schools is drawing some criticism after New York City Police Commissioner William J. Bratton said New York schools received the same threat, which they did not deem credible. New York Mayor Bill de Blasio called the emailed threat "so generic, so outlandish" that it was obviously a hoax, the New York Times reported.

It's impossible to know whether the Los Angeles student would still be alive had schools been open. But the incident underscores how our assessments of various risks are often wildly at odds with the actual dangers posed by them. As Wall Street Journal columnist Greg Ip argues in a recent book, things we do to keep ourselves safe may actually put us in even more danger.

We buy guns for self-defense, for instance -- even though having a gun in the home increases your risk of being murdered or killing yourself, and guns are used at least as often against family members as they are against intruders. Companies proudly proclaim their aversion to genetically modified food, while overlooking the far more common dangers posed by food-borne illnesses.

In government, policymakers stoke fear of marijuana -- which has no known toxic dose -- while ignoring the hundreds of thousands of annual deaths due to alcohol and tobacco. They respond to the deaths of 2,977 Americans in a terror attack by sending thousands more soldiers to die in Iraq and Afghanistan.

Policymakers, in theory, are supposed to be able to draw on data and the experience of experts to protect us from the real dangers, rather than the imagined ones. But politicians are simply people, and too often they're subject to the same irrational fears and overreactions as the rest of us. The risk of dying in a terror attack is about the same as the risk of getting crushed by falling furniture.

It goes without saying that the odds of getting killed by a car are much, much higher than either of those. If the reports out of Los Angeles are accurate, it appears that policymakers failed to keep these odds in perspective when deciding to shut down schools on the basis of an email.