N.J. Stat. § 27:7-9
If, when a highway is taken over by the state under this chapter, a county shall have improved, reconstructed or made any extraordinary repairs upon it or any part thereof, under a contract awarded after March first, one thousand nine hundred and twenty-seven, the commissioner shall first set aside from the funds under his control a sum of money sufficient to reimburse the county for all money expended by it on such work whether raised by the issuance of bonds or otherwise, exclusive, however, of all moneys which may have been received by the county in the form of state aid, and expended as part of the cost of such extraordinary repairs or reconstruction.
No such repayment shall be made, by virtue of any award of contract made after March thirtieth, one thousand nine hundred and twenty-seven, unless some proceeding concerning the contract had been theretofore begun or the contract shall have been theretofore approved by the commissioner.
For the purpose of determining the amount of money expended by the county, the county engineer shall prepare and file with the commissioner a detailed certificate of the moneys so expended which shall be accepted as fixing the amount expended by the county provided the work shall be equal to that required by the provisions of this chapter.
N.J.S. § 27:7-9