Iowa Code § 313.37: Road equipment.

The department is authorized to purchase road material or road machinery required in the improvement or maintenance of the primary roads, after receiving competitive bids, and to pay for the same out of the primary road fund, and is directed to purchase, rent or lease any machinery or other articles necessary for the use and most economical operation of the field engineering work, the testing of materials, the preparation of plans, and for all allied purposes, in order to enable the department to carry out the provisions of this chapter.