This is the key vulnerability of high speed rail.
Terrorists can tunnel under the tracks to set charges, set off a nearby truck bomb, or simply put a steel beam over the tracks in front of the oncoming train.
This is far simpler than taking down an aircraft and with greater loss of life.
For us, the ONLY path to safety is to identify potential jihadis and capture them before they can launch an attack.
Our problem is not with devices; our problem is certain people with a certain twisted ideology.
In the long run, we must defeat the ideology just like we defeated Nazi facism.
Good points Darth.