Except as provided by subsection (b), in any case in which a covered beneficiary is referred by a primary care physician to a specialty care provider who provides services more than 100 miles from the location in which the primary care provider provides services to the covered beneficiary, the Secretary of Defense shall provide travel and transportation allowances as specified in regulations prescribed under section 464 of title 37 for the covered beneficiary and, when accompaniment by an adult is necessary, for a parent or guardian of the covered beneficiary or another member of the covered beneficiary’s family who is at least 21 years of age.