The right-of-way of the Frederick and Buckeystown Turnpike was resurfaced with macadam by 1921. The remainder of Buckeystown Pike was paved as a concrete road from south of Buckeystown to around Lily Pons Road in 1918 and 1919 and south of Lily Pons Road to just north of the modern MD 28 junction in Tuscarora by 1921. The concrete highway was extended south through the MD 28 junction to modern MD 28's junction with Nolands Ferry Road by 1923. That same year, Emmitsburg Pike was paved through Thurmont. In 1926, MDSRC assumed maintenance of and resurfaced Market Street with asphalt from the city of Frederick between the south city limit at New Design Road (now Stadium Drive) to the north city limit at 9th Street. The commission also replaced Buckeystown Pike's covered bridge at Ballenger Creek with the modern concrete arch bridge that year. US 15 was widened to a width of from Frederick to the Pennsylvania state line around 1930. The highway from Tuscarora to Point of Rocks was constructed as a concrete road in three stages starting in 1929, when the paved highway was extended west from Nolands Ferry Road to west of New Design Road. The second section of the new highway was started in 1930. The third segment was finished in 1933, which completed the paving of US 15 in Maryland. Around 1938, the U.S. Highway was resurfaced with asphalt from Emmitsburg to the Pennsylvania state line and from the south end of Frederick to Evergreen Point; in addition, a grade separation was constructed with the Western Maryland Railway in Thurmont.