U.S. regulators have closed an inquiry into five of the largest U.S. airlines after finding no price gouging or unfair changes to service following a 2015 Amtrak crash that shut down trains in the Northeast.

Investigators found that fares increased on some routes and decreased on others after the derailment and that there were “no unconscionable increases” of prices beyond normal levels, the Transportation Department said in a letter to the airlines on Wednesday.

American Airlines Group Inc., Delta Air Lines Inc., United Continental Holdings Inc., Southwest Airlines Co. and JetBlue Airways Corp. were part of the probe.

The investigation is separate from a broader Justice Department inquiry into possible price collusion among the four largest airlines in the U.S.

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This article was written by Mary Schlangenstein from Bloomberg and was legally licensed through the NewsCred publisher network.

Photo Credit: After a May 2015 Amtrak crash in Philadelphia, airlines raised their prices in the region, but their actions were not illegal, the DOT found. Joseph Kaczmarek / Associated Press