Maryland Route 166 is a state highway in the U.S. state of Maryland. The state highway runs 2.71 miles (4.36 km) from Interstate 195 (I-195) in Arbutus north to MD 144 in Catonsville. MD 166 consists of two sections: a short freeway section that serves as a northern continuation of I-195 and provides access to the University of Maryland, Baltimore County (UMBC), and a segment of Rolling Road, a major north–south highway in western Baltimore County. Rolling Road dates to the colonial era as a highway used to transport tobacco from plantations to river ports. North Rolling Road, which connects Catonsville with Woodlawn and Milford Mill, has always been a county highway. South Rolling Road was constructed as a state highway by the early 1920s between what were to become U.S. Route 1 and US 40. Parts of South Rolling Road were transferred to county maintenance after they were severed by the construction of I-95 and a freeway relocation of the southern end of MD 166 in the early 1970s.

Interstate 195 (I-195) is an auxiliary Interstate Highway in the US state of Maryland. The highway runs 4.35 miles (7.00 km) from I-95 in Arbutus east to Maryland Route 170 (MD 170) near the Baltimore/Washington International Airport in Linthicum. I-195, which is also known as Metropolitan Boulevard, is the main connection between the airport terminal and highways leading to Baltimore, Washington, D.C., and Annapolis, including I-95, MD 295, and I-97. The interchange with MD 170, which forms part of the Airport Loop, provides access to various airport-related services. I-195 also links I-95 with Catonsville and the University of Maryland, Baltimore County (UMBC), via a westward continuation of Metropolitan Boulevard that is part of MD 166.