(a) All bridges are obstructions to navigation and are tolerated only as long as they serve the needs of land transportation while allowing for the reasonable needs of navigation.(b) This part describes the general procedures by which the U.S. Coast Guard determines a bridge to be an unreasonable obstruction to navigation and issues an Order to Alter under the authority of the following statutes, as appropriate: Section 18 of the Rivers and Harbors Appropriations Act of 1899, 33 U.S.C. 502 ; Section 4 of the Bridge Act of 1906, 33 U.S.C. 494 ; or the Truman-Hobbs Act of 1940, as amended, 33 U.S.C. 511-524 .(c) A bridge constructed across a navigable water of the United States shall not unreasonably obstruct the free navigation of the water over which it was constructed, either due to insufficient height or width of the navigation span, or because of difficulty in passing through the draw opening. If any bridge unreasonably obstructs navigation, the Commandant, U.S. Coast Guard, will order the alteration of that bridge. Alterations may include structural changes, replacement, or removal of the bridge.(d) Whenever the Coast Guard has good reason to believe that a bridge across any of the navigable waters of the United States is an unreasonable obstruction to navigation, the Coast Guard will give notice to the owner of the bridge and other interested parties, and hold a public meeting at which the interested parties will have a full opportunity to be heard and to provide information on the question of whether alterations to the bridge are necessary and, if so, the extent of alterations needed.(e) If the Coast Guard determines that alterations to a bridge are necessary, the Commandant, U.S. Coast Guard, will issue to the bridge owner an Order to Alter containing details of the alterations necessary to render navigation through or under the bridge reasonably free, easy, and unobstructed. (1) In the case of a railroad or publicly owned highway bridge, an Order to Alter is issued to the bridge owner under the provisions of the Truman-Hobbs Act (33 U.S.C. 511 et seq.). In ordering these alterations, the Coast Guard will give due regard to the necessities of free and unobstructed navigation and of rail and highway traffic. For alterations to bridges governed by the Truman-Hobbs Act, the Coast Guard must approve general plans, specifications, and contracts for the alteration project, as well as approving the apportionment of the total cost of the alterations between the United States and the bridge owner.(2) For all other bridges, the Order to Alter will contain the required alterations for the bridge and will prescribe a reasonable time in which to accomplish the required alterations. The bridge owner is responsible for the entire cost of the required alterations.CGD 91-063, 60 FR 20902, Apr. 28, 1995, as amended by USCG-2010-0351, 75 FR 49410 , Aug. 13, 2010