(a) Effective Periods of Licenses. - The Secretary of Transportation shall specify the period for which a license issued or transferred under this chapter is in effect. (b) Modifications. - On the initiative of the Secretary or on application of the licensee, the Secretary may modify a license issued or transferred under this chapter if the Secretary decides the modification will comply with this chapter. (c) Suspensions and Revocations. - The Secretary may suspend or revoke a license if the Secretary decides that - (1) the licensee has not complied substantially with a requirement of this chapter or a regulation prescribed under this chapter; or (2) the suspension or revocation is necessary to protect the public health and safety, the safety of property, or a national security or foreign policy interest of the United States. (d) Effective Periods of Modifications, Suspensions, and Revocations. - Unless the Secretary specifies otherwise, a modification, suspension, or revocation under this section takes effect immediately and remains in effect during a review under section 70110 of this title. (e) Notification. - The Secretary shall notify the licensee in writing of the decision of the Secretary under this section and any action the Secretary takes or proposes to take based on the decision.