U.S. Route 29 (US 29) is a north–south United States Numbered Highway that runs for 1,043.3 miles (1,679.0 km) from Pensacola, Florida, to the western suburbs of Baltimore, Maryland. In the U.S. state of Maryland, US 29 is a major highway that emerges from Washington DC and runs north into eastern Montgomery County, stretching over 25.86 miles (41.62 km) through the state and terminating at Maryland Route 99 (MD 99) outside of Ellicott City. It serves the cities of Columbia and Ellicott City and provides the westernmost north–south route between Washington DC and Baltimore.

Maryland Route 99 is a state highway in the U.S. state of Maryland. Known as Old Frederick Road, the state highway runs 7.57 miles (12.18 km) from MD 32 near West Friendship east to U.S. Route 29 in Ellicott City. MD 99 parallels the north side of Interstate 70 (I-70) through a rural and suburban area in northeastern Howard County. MD 99, which follows the original 18th-century road west from Baltimore, was constructed as part of three state highways: MD 99, the original MD 100, and MD 105. All three highways were constructed between the early 1920s and early 1930s. MD 99 originally turned south along St. Johns Lane to US 40 and MD 144; in 1956, the state highway was rerouted along part of MD 100 and all of MD 105 to downtown Ellicott City. MD 99's eastern terminus was rolled back to US 29 in two steps in the late 1970s and late 1980s.