Maryland Route 166 (MD 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