You don’t even need explosives. Just pull out the spikes on the outside rail of a curve. As long as you don’t break the rail the signals will all stay green. A light weight train derailment at 200 miles per hour isn’t a whole lot different from a plane crash. Go look at pictures from the ICE wreck when it piled up under a highway bridge.
You don’t even need to do that. Weld a “derail” on the track.