If the secretary of the United States department of transportation finds any part of this chapter to be in conflict with federal requirements that are a prescribed condition to the allocation of federal funds to the state, the conflicting part of this chapter is hereby declared to be inoperative solely to the extent of the conflict and with respect to the agencies directly affected, and such finding or determination shall not affect the operation of the remainder of this chapter in its application to the agencies concerned. The rules under this chapter shall meet federal requirements that are a necessary condition to the receipt of federal funds by the state.