Maryland Route 45 is a state highway in the U.S. state of Maryland. Known for most of its length as York Road, the state highway runs 30.06 miles (48.38 km) from U.S. Route 1 /US 40 Truck in Baltimore north to the Pennsylvania state line in Maryland Line, where the highway continues as State Route 3001. MD 45 is the primary highway between Downtown Baltimore and Towson, the county seat of Baltimore County. North of Interstate 695 (I-695), the state highway parallels I-83 and serves the suburban communities of Lutherville, Timonium, Cockeysville, and Hunt Valley. MD 45 also connects the northern Baltimore County communities of Hereford and Parkton. The state highway is maintained by the Maryland State Highway Administration in Baltimore County and by the Baltimore City Department of Transportation in the city, where the highway also follows Greenmount Avenue.

U.S. Route 1 (US 1) is the easternmost and longest of the major north–south routes of the older 1920s era United States Numbered Highway System, running from Key West, Florida, to Fort Kent, Maine. In the U.S. state of Maryland, it runs 81 miles (130 km) from the Washington, D.C. line to the Pennsylvania state line near the town of Rising Sun.