Expenditures by the department of transportation shall be made upon vouchers signed by the director of transportation; provided that the director, may, in writing, designate a qualified subordinate to sign vouchers, make routine reports, and perform other routine business duties, subject to the direction of the director, for whose acts the director shall be responsible.

The department may cause work to be performed by day labor or by contract or by any other method deemed by the department to be most advantageous to the State.