Iowa Code § 313.1: Federal and state cooperation.

The department is empowered on behalf of the state to enter into any arrangement or contract with and required by the duly constituted federal authorities, in order to secure the full cooperation of the government of the United States, and the benefit of all present and future federal allotments in aid of highway construction, reconstruction, improvement or maintenance. The good faith of the state is hereby pledged to cause to be made available each year, sufficient funds to equal the total of any sums now or hereafter apportioned to the state for road purposes by the United States government for such year, and to maintain the roads constructed with said funds.