(4) Screening defined .— In this subsection the term “screening” means a physical examination or non-intrusive methods of assessing whether cargo poses a threat to transportation security. Methods of screening include x-ray systems, explosives detection systems, explosives trace detection, explosives detection canine teams certified by the Transportation Security Administration, or a physical search together with manifest verification. The Administrator may approve additional methods to ensure that the cargo does not pose a threat to transportation security and to assist in meeting the requirements of this subsection. Such additional cargo screening methods shall not include solely performing a review of information about the contents of cargo or verifying the identity of a shipper of the cargo that is not performed in conjunction with other security methods authorized under this subsection, including whether a known shipper is registered in the known shipper database. Such additional cargo screening methods may include a program to certify the security methods used by shippers pursuant to paragraphs (1) and (2) and alternative screening methods pursuant to exemptions referred to in subsection (b) of section 1602 of the Implementing Recommendations of the 9/11 Commission Act of 2007.