A common or contract carrier shall be liable under other law in lieu of
section 9607 of this title 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:
Provided, however, 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.