Hyperloop as terrorist target

There is an extraordinary disconnect between the reporters covering the hyperloop and the scientists and engineers who actually work in this field. With the possible exception of self-sustaining Martian colonies, there is no area where what you read in mainstream publications like the New York Times or the Atlantic will so completely contradict what you hear from independent experts. For the most part, the reporters aren't even aware of the questions they should be asking.

Case in point.

Other than this one somewhat superficial but otherwise pretty good article in the National Interest, there has been virtually no coverage of the hyperloop's unique vulnerability to terrorist attack. This is an enormously complicated issue, but there are certain aspects of it which are obvious to anyone who has seriously looked at the problem even though they very seldom make it into the breathless puff pieces we've come to expect.

Near top of mind for any engineer who has given the question of safety any thought is what will happen if there is a breach in the tube and the vacuum is compromised. At that point, a wall of air traveling at the speed of sound goes barreling down the tube in both directions. For those pods traveling toward the wall at nearly the speed of sound, it will certainly not turn out well. All of the occupants of the first pod will die instantly. What happens next is impossible to determine without extensive tests, but even allowing for the best-case scenario, you will have hundreds of people who need to be evacuated

From the tube which needs to be repressurized immediately. The passengers will then need to make their way to the closest escape hatch. The hatches themselves will present a considerable engineering challenge since they will need to be not only airtight but completely inaccessible from the outside lest they become yet another point of attack.

After you get these people out of the hundreds of miles of tube, you have to do something about the pods themselves. Keep in mind, the primary propulsion and braking of the pods is provided by linear induction motors at either end. I'm not going to spend a lot of time speculating on the best way of getting the pods out of the tube, but it is safe to say it will be neither trivial nor quick.

Then comes the massive job of getting the system back up and running. Not only will you have to replace the section with the original breach, you will have to completely clean the tube of debris, quite a bit of which will undoubtedly be sucked in. Then you will have to inspect every inch of the tube for structural damage and double-check every seal, escape hatch, thermal expansion joint, and other potential point of failure. You will have to make sure that there was no damage done to the magnetic levitation track. You will have to make absolutely certain that the pods are in perfect working order since, when running through the system, a loss of cabin pressure in one of these things means instant death for everyone inside.

There are few systems of Transportation infrastructure where a single attack can produce this level of damage and economic disruption. Of these, none offers the variety vulnerable points that the hyperloop does. If we are talking about elevated tracks, which seems to be the primary approach being proposed, every section of tube and every pylon supporting it is a potential point of attack. Hardening all of those targets might be possible, but it would be unimaginably expensive.