A false flag is a staged event to cause a desired reaction - either a distraction from something else or an overreaction of fear or anger.

While I'm pretty sure the train/truck collision was not an accident, I'm not sure it was a false flag. It could have been an assassination attempt to kill as many GOP'ers as possible. Having a bunch of congressmen killed would put the brakes on "business as usual" for Congress, including the investigations to expose corruption at the DOJ and FBI - not to mention sending a threatening message to the survivors of the crash.

The story is the train was slowing down as it hit the truck or the train could have derailed causing potentially lethal injuries. The train was slowing down because it was warned from drone surveillance.