(1)    When a portion of the system of county aid highways in any city is to be improved, and the funds from the city and county are available therefor, the city may determine that the roadways shall be paved to a greater width than 18 feet. If it so decides, the city may determine the type of improvement, the width, and all other features of the construction, subject to the approval of the county highway committee. And said committee shall fix the amount per linear foot of the improvement to be paid by the county. The city shall then improve the street in the manner provided generally for making street improvements. The work shall be done under the supervision of the city, but subject to the inspection of the county highway commissioner.

   (2)   Upon the completion of the work the county’s share of the cost shall be paid to the contractor as though the county had been an immediate party to the contract. Unless specifically authorized by the county, the payment by the county shall not exceed the cost of 22 feet of the width of the pavement, as well as a portion of the costs of grading, draining, and appertaining structures. The balance of the expense of the improvement shall be borne by the city, and shall be provided in the manner in which expense of street improvement is ordinarily met. Assessments of benefits may be made by the city against abutting property in the manner provided where the improvement is done solely at the expense of the city, but such assessments of benefits shall not exceed the difference between the cost of the improvement and the amount contributed thereto by the county.

   (3)   The provisions of subs. (1) and (2) shall apply to villages and towns subject to the approval of the county board.