The section of the Post Road between Bel Air Avenue in Aberdeen and the former racetrack in Havre de Grace, much of which is now MD 132, was paved under the state aid system as a wide macadam road by 1911. The first section of the gap between Rossville and Aberdeen was filled with a concrete road from Bradshaw to Winters Run by 1921. The remainder of the highway in Baltimore County and the section from Winters Run to Bynum Run were paved in concrete by 1923. The final piece of Philadelphia Road in Harford County was completed as a concrete road from Bynum Run to Aberdeen in 1926. The highway was paved in concrete along Main Street and Delaware Avenue through Elkton, with the exception of a gap at the west end of town, by 1923. The gap between Elkton and the Delaware state line was filled in 1925. The gap at the west end of Elkton was left in inferior condition in anticipation of a grade separation of the Pennsylvania Railroad. This grade separation and its approaches was completed in 1929, completing US 40, which had been assigned to the length of the Philadelphia Road in 1927.