All construction or improvement performed under this chapter shall be under the direction of the board of county commissioners, acting by and through the county road engineer, or such other engineer as the board of county commissioners shall designate. Contracts let and/or work performed upon all construction or improvement hereunder shall be in accordance with the laws pertaining to work upon county roads. The construction and improvement standards of the respective counties for engineering and performance of work, shall apply to all construction or improvement under this chapter.