Waterloo Road was built as a macadam road in 1932 from
U.S. Route 1 (US 1) in
Jessup north to MD 103 in Ellicott City; the highway was designated MD 531. MD 531 was replaced with a northern extension of MD 175 from Jessup to Ellicott City by 1946. Old Annapolis Road was designated MD 539 in 1956; that highway became part of an extended MD 108 in 1960 when
US 29 was moved to Columbia Pike from
Silver Spring to Ellicott City. After MD 175 was rerouted along Little Patuxent Parkway (now named Rouse Parkway) from west of
Interstate 95 (I-95) to
Columbia Town Center around 1977, MD 108 was extended east to its present terminus near I-95. The portion of Waterloo Road between MD 108 and MD 103 was designated MD 104 by 1979. When MD 100 was under construction between MD 104 and I-95 in the late 1990s, a standard intersection with MD 104 served as the eastern terminus of the two-lane, disjoint section of MD 100 between US 29 and MD 104. MD 104's interchange with MD 100 was completed in 1998 concurrent with the portion of the freeway from MD 104 to I-95. ==Junction list==