That's because dying in a plane is much scarier than dying in a bus. I mean, think about it, you're trapped up there... if the plane blows up, you blow up with it. If you're on a bus... oh wait, you also die in a fire. But on the news the plane crash looks scarier -- more people can see it, and more people are irrationally afraid of flying.

Think about how Americans handle risk; the risk of dying in a plane hijacking is very low. The risk of dying of heart disease if you don't eat well is very high. So we spend a ton of time, effort, and money on preventing plane hijackings, but we eat tons and tons of unhealthy food. You'd think that the reason we have security is to prevent ourselves from dying, but if that's the case, we're doing it very wrong. The reason we have airport security is so that some bureaucrat can get a promotion; armed guards with high-tech tools make people feel like their government loves them. (Except for people with a brain, who think it's a little scary to have to show the cops your charlie browns every time you board a plane.)

I don't even want to think about how much healthy food we could buy with the money we spend on full-body imagers.

In Spain, there are metal detectors and x-ray machines at the gates to the train platforms. In Israel, there are metal detectors and x-ray machines at the bus terminals. Security seems to be mostly reactive - people blow up a train (Spain), you get frisked boarding an intercity train. People blow up buses (Israel), you x-ray luggage and pat down people entering the bus terminal.

It's awfully hard to crash a train into a building :-)

? Hollywood teaches us two ways: Go quickly around a corner in a city. Don't put on the brakes when getting to a end of a track.

But still, it's a lot harder to crash a train into an arbitrary building, not just whatever building happens to be at a corner or at the end of the track.