23 CFR 140.922: Billings.

(a) After the executed State-Railroad Agreement has been approved by FHWA, the company may be reimbursed on progress billings of incurred costs. Costs for materials stockpiled at the project site or specifically purchased and delivered to the company for use on the project may be reimbursed on progress billings following approval of the executed State-Railroad Agreement or the written agreement under 23 CFR 646.218(c).

(b) The company shall provide one final and complete billing of all incurred costs, or of the agreed-to lump sum, within one year following completion of the reimbursable railroad work. Otherwise, previous payments to the company may be considered final, except as agreed to between the SHA and the railroad.

(c) All company cost records and accounts relating to the project are subject to audit by representatives of the State and/or the Federal Government for a period of three years from the date final payment has been received by the company.

(d) A railroad company must advise the State promptly of any outstanding obligation of the State's contractor for services furnished by the company such as protective services.