Iowa Code § 327D.43: Routing intrastate shipments.

It shall be the duty of every common carrier subject to the provisions of this chapter, when shipments are tendered for transportation between points in this state, to route such shipments from shipping point to point of destination over the cheapest available route between such points except in cases where the shipper, in shipping orders or bills of lading, specifically designates a particular route over which it is desired such shipments shall be moved.