Delaware has about 1,450 bridges, 95 percent of which are under the supervision of DelDOT. About 30 percent of all Delaware bridges were built before 1950, and about 60 percent of the number are included in the National Bridge Inventory. Some bridges not under DelDOT supervision includes the four bridges on the Chesapeake and Delaware Canal, which are under the jurisdiction of the U.S. Army Corps of Engineers, and the Delaware Memorial Bridge, which is under the bi-state Delaware River and Bay Authority.