National Bridge Replacement and Improvement Act This bill directs the Department of Transportation (DOT) to establish a national bridge replacement and improvement grant program. Under the program, DOT may provide competitive grants to governmental entities and planning organizations to assist a bridge project that is eligible for federal-aid highway funding and will (1) restore or increase the structural capacity of the bridge; (2) correct a major safety defect of the bridge; or (3) replace an existing bridge with a new bridge that meets specific requirements, including being located in the same general traffic corridor as the bridge being replaced.