N.D. Cent. Code § 24-01-37

The department, at least every four years, and so far as time and conditions may permit, shall cause an inspection to be made of all bridges on the state highway system in the state. In case any bridge on the state highway system is deemed unsafe for public use by the said department, it forthwith shall take steps to close the same and prevent the use thereof by the public. In case any bridge on the state highway system is deemed unsafe for loads in excess of a certain weight, the department forthwith shall post notices on both ends of such bridge stating that such bridge is unsafe for loads beyond that weight.