((a)) Each hazardous substance which is listed or designated as provided in shall, within 30 days after , or at the time of such listing or designation, whichever is later, be listed and regulated as a hazardous material under chapter 51 of title 49.
((b)) A common or contract carrier shall be liable under other law in lieu of for damages or remedial action resulting from the release of a hazardous substance during the course of transportation which commenced prior to the effective date of the listing and regulation of such substance as a hazardous material under chapter 51 of title 49, or for substances listed pursuant to subsection (a) of this section, prior to the effective date of such listing: , That this subsection shall not apply where such a carrier can demonstrate that he did not have actual knowledge of the identity or nature of the substance released.