By 1930, US 1 had been widened to throughout Harford County with the construction of concrete shoulders. Widening of Belair Road to from Baltimore County to downtown Bel Air was underway by 1934 and completed in 1936. By 1938, US 1 entered downtown Bel Air on the Baltimore Pike, turned north onto Bond Street, followed Main Street—which in 1938 also became part of MD 24—to Broadway, then followed Broadway to Hickory Avenue. Around 1940, the portions of Bond and Main streets that carried US 1 were expanded to in width. US 1 was expanded further following World War II: the highway was reconstructed and widened from downtown Bel Air through Hickory between 1950 and 1952 and from Benson to Bel Air by 1954.
