A truck passes over the train tracks near a sign listing an emergency number for railroad problems on Tuesday, March 10, 2015, in Halifax, N.C.  A train collided with a truck, Monday injuring 55 people.  The truck with a state trooper escort become stuck in the crossing but no calls were made to Amtrak about the problem, even though the sign should have been visible to the truck driver.  (AP Photo /Jonathan Drew)

Investigators seek cause of Amtrak crash that injured 55

Among the evidence will be the locomotive’s “black box” recovered at the scene and the special state permit that allowed the trucking company to exceed length and weight limits as it hauled an electrical distribution facility headed to New Jersey.