The proposed state road continued along what are today a series of county routes: Cub Hill Road, Glen Arm Road, and Manor Road to its intersection with Long Green Road in the community of Unionville or Long Green. Harford Road was under construction by 1911 from North Avenue to Taylor Avenue and completed in 1912. From North Avenue to the old city limits near Lake Montebello, Harford Road was reconstructed with a vitrified brick surface. From the city limits to Taylor Avenue, the highway was built with a wide tarred macadam surface. The old turnpike along what is now Harford Road was resurfaced from Taylor Avenue northeast to Little Gunpowder Falls by 1915. The Harford County portion of Harford Road was reconstructed starting in 1926. The highway was completed as a macadam road from US 1 in Benson west to Rocky Branch in 1927. The remainder of Harford Road south to Little Gunpowder Falls was built as a concrete road in 1928. By 1930, the portion of Harford Road in Baltimore city and county was widened to a width of . Harford Road was marked as MD 147 by 1933. Between 1936 and 1938, the tracks of a defunct interurban were removed and the space used to widen MD 147 to a width of from the Baltimore city line to Carney. That portion of MD 147 was widened again with the addition of a wide concrete shoulder around 1940. In 2018, a roundabout was constructed at Glen Arm Road/Mt. Vista Road.