Interstate 170 was a planned spur to the north side of Downtown Baltimore from I-70 in the western portion of the city. Approved by the American Association of State Highway and Transportation Officials (AASHTO) on June 30, 1970, the short section of I-170 was completed in 1979.
With the withdraw of Interstate 70 through Leakin Park in Baltimore, there would be no connection from I-170 to the parent route. A subsequent proposal by the Maryland State Highway Administration (MDSHA) turned the freeway spur along I-170 southward over the easternmost segment of what was planned for I-70 to an interchange with Interstate 95 by Carroll Park. Since the route no longer connected with I-70, it was renumbered as Interstate 595. The Federal Highway Administration (FHWA) approved the renumbering on July 2, 1982.
The MDSHA application both eliminating I-170 and a portion of I-70 and establishing I-595 was approved by AASHTO on November 20, 1982. The Proposed Interstate Route Description defined I-595 as:
From a junction with FAI Route 95, east of U.S. Route 1, northerly then easterly to a junction with Green Street, just east of Harbor City Boulevard. A distance of approximately 3.60 miles.
Construction completing the link from what was I-170 to I-95 as Interstate 595 never came to fruition. I-170 was signed along the route until 1983, when U.S. 40 replaced it from adjacent Franklin and Mulberry Streets. I-595 was eventually reused in 1989 along U.S. 50/301 from the Capital Beltway east to Annapolis.