U.S. Route 40 Alternate (US 40 Alternate) is an alternate route of US 40 in the U.S. state of Maryland. The highway runs from Potomac Street in Hagerstown east to US 40 in Frederick. US 40 Alternate parallels US 40 and much of Interstate 70 (I-70) to the south through eastern Washington County and western Frederick County. The alternate route connects Hagerstown and Frederick with Funkstown, Boonsboro, Middletown, and Braddock Heights. US 40 Alternate crosses two major north–south components of the Blue Ridge Mountains that separate the Great Appalachian Valley and the Piedmont: South Mountain between Boonsboro and Middletown and Catoctin Mountain, which is locally known as Braddock Mountain, at Braddock Heights. US 40 Alternate is the old alignment of US 40. The highway's path was blazed in the mid-18th century to connect the Hagerstown Valley and Shenandoah Valley with eastern Pennsylvania and central Maryland. In the early 19th century, US 40 Alternate's path was improved as part of a series of turnpikes to connect Baltimore with the eastern terminus of the National Road in Cumberland. The highway was improved as one of the original state roads in the early 1910s and designated US 40 in the late 1920s. Construction on a relocated US 40 between Hagerstown and Frederick with improved crossings of South Mountain and Braddock Mountain began in the mid-1930s; the new highway was completed in the late 1940s. US 40 Alternate was assigned to the old route of US 40 in the early 1950s. Route description US 40 Alternate is a part of the National Highway System as a principal arterial from Edgewood Drive in Funkstown to its underpass of I-70 south of Funkstown and from Old Hagerstown Road near Middletown to US 40 in Frederick. Hagerstown to South Mountain US 40 Alternate begins as Baltimore Street at its intersection with one-way southbound Potomac Street within the Hagerstown Historic District on the southern edge of downtown Hagerstown. Baltimore Street, which continues west as a city street toward the Hagerstown City Park, runs east–west two blocks south of US 40, which comprises a one-way pair of Washington Street eastbound and Franklin Street westbound. After heading east for two blocks, during which US 40 Alternate intersects one-way northbound Locust Street, the municipally-maintained alternate route turns southeast onto Frederick Street at a five-way junction that also includes north–south Mulberry Street. US 40 Alternate intersects Memorial Boulevard, which heads east past