WASHINGTON/NEW YORK (Reuters) – The U.S. Transportation Department is investigating possible price gouging by the five biggest U.S. airlines while train service was disabled between New York and Washington following a deadly Amtrak crash in May, it said on Friday. The review involves Delta Air Lines Inc (DAL.N), American Airlines Group Inc (AAL.O), United Continental Holdings Inc (UAL.N), Southwest Airlines Co (LUV.N) and JetBlue Airways Corp (JBLU.O), all of which said they were cooperating with the probe.