(a) Commencing with annual reports for the year 1978 or for any portion thereof until further order, all class I railroad companies including class I switching and terminal companies subject to section 20 of the Interstate Commerce Act as amended shall separate operating expenses common to both freight service and passenger service in accordance with the regulation in this part.

(b) The carrier shall maintain records supporting its common operating expense apportionments to freight and passenger services. The carrier shall report common expense apportionments to the Board as required.