A train is derailed west of Casselton, North Dakota

U.S. companies moving crude oil via rail must tell state officials when a cargo is moving across their jurisdiction, the U.S. Transportation Secretary said on Wednesday, the latest response to a string of fiery derailments.

Transportation Secretary Anthony Foxx, at a hearing of the Senate Commerce Committee, also said DOT-111 tank cars, currently the workhorse of the fast-growing oil-by-rail sector, were not fit for such cargo and should be avoided or reinforced wherever possible.