I-595 in Maryland is the longest unsigned route within the Interstate Highway System. Aligned entirely along U.S. 50 (John Hanson Highway) and partially along U.S. 301, I-595 follows John Hanson Highway between I-95/495 (Capital Beltway) and MD 70 at Annapolis. U.S. 50/301 extend east from I-595 across the Severn River and Chesapeake Bay Bridge.
Maryland applied to the American Association of State Highway and Transportation Officials (AASHTO) on November 15, 1975 to redesignate the freeway along U.S. 50 between the Capital Beltway and a point west of Annapolis as Interstate 68. AASHTO instead opted to conditionally approve the western portion of the route as an extension of Interstate 97, and the eastern section as Interstate 197. Neither of these routes were signed and construction had yet taken place on I-97 northward when Maryland again applied to AASHTO on October 3, 1981 for the I-68 designation along U.S. 50. This application included renumbering the I-197 leg as Interstate 168 however. Finally on June 7, 1989, AASHTO approved renumbering U.S. 48 and the National Freeway in western Maryland as Interstate 68, and the former I-68 proposal along U.S. 50/301 as Interstate 595.
John Hanson Highway, U.S. 50 from D.C. east to Annapolis was upgraded starting in the mid-1980s. Work focused on modernizing the aging freeway by replacing overpasses, redesigning interchanges and adding lanes. Further widening commenced in May 1992 with expansion to six and eight lanes from Interstate 97 to just west of the Patuxent River. The $93 million project included the replacing the compact cloverleaf interchange with U.S. 301/MD 3.1
Upon completion of the freeway upgrade in 1995, U.S. 50 was to be cosigned as Interstate 595. However since travelers were already familiar with the U.S. 50 and U.S. 301 designations, officials reconsidered signing I-595 and instead opted to designate it a hidden route. However, some signs for U.S. 50 posted in the early 1990s were designed with space reserved for Interstate 595 shields.