U.S. Route 340 in Maryland - Route Description

Route Description

US 340 enters Maryland at the Potomac Water Gap just south of the confluence of the Potomac River and the Shenandoah River at Harpers Ferry. The Potomac Water Gap is where the Potomac River passes between two sets of ridges. The first set of ridges is Elk Ridge to the north, also known as Maryland Heights, and Blue Ridge Mountain, which forms the border between West Virginia and Virginia, to the south. The second set of ridges is South Mountain in Maryland and Short Hill Mountain in Virginia. US 340 passes along the northern edge of Blue Ridge Mountain then passes through the northwestern corner of Loudoun County, Virginia before crossing the Potomac River at an angle, running southwest–northeast on a two-lane steel continuous deck truss bridge at the community of Sandy Hook. On the Maryland side, the bridge also crosses the Chesapeake and Ohio Canal, CSX's Cumberland Subdivision, and Sandy Hook Road, the original alignment of US 340.

Just north of the bridge, US 340 is named Jefferson Pike and widens to a two-lane divided highway that intersects Valley Road and Keep Tryst Road; the sweeping ramp from northbound US 340 to Keep Tryst Road is the old alignment of US 340. Beyond the intersection, the U.S. highway curves to the east, expands to four lanes, and meets the southern end of MD 67 (Rohrersville Road) at a trumpet interchange in Weverton. After the highway crosses Israel Creek, the eastbound direction of US 340 has a right-in/right-out intersection with the eastern end of Keep Tryst Road. The U.S. highway becomes a freeway with a speed limit of 65 miles per hour (105 km/h) that parallels the C&O Canal and the railroad line, now part of the Metropolitan Subdivision, between the river and the southern end of South Mountain into Frederick County, where US 340's name changes to Jefferson National Pike and the highway meets the western end of MD 180 (Jefferson Pike) at a partial interchange near Knoxville. There is no access from westbound US 340 to eastbound MD 180 or from westbound MD 180 to eastbound US 340.

US 340 veers away from the Potomac River and passes through farmland of the Catoctin Valley, paralleled by its old alignment, MD 180, at a distance to the south. The U.S. highway meets MD 17 (Burkittsville Road) at a diamond interchange near Rosemont and crosses Little Catoctin Creek. East of Petersville, US 340 has a diamond interchange with MD 180 and crosses Catoctin Creek. On the western edge of Jefferson, westbound US 340 receives a ramp from MD 180. Full access to Jefferson is provided by a diamond interchange with Lander Road. The U.S. highway passes through a wide gap in Catoctin Mountain and has a partial interchange with US 15 (Catoctin Mountain Highway), which heads south toward Point of Rocks. US 15 and US 340 join in a concurrency that lasts through US 340's eastern terminus in Frederick. Access from northbound US 15 to westbound US 340 and from eastbound US 340 to southbound US 15 is provided through performing a U-turn at the next interchange, a diamond interchange with Mt. Zion Road.

US 340 and US 15 cross over Ballenger Creek and the freeway's speed limit drops to 55 miles per hour (89 km/h) before the highways approach a series of three interchanges on the southwest side of Frederick. The highway's partial interchange with I-70 (Eisenhower Memorial Highway) features ramps from eastbound I-70 to both directions of US 340, a ramp from westbound I-70 to westbound US 340, and a ramp from eastbound US 340 to eastbound I-70 and access to southbound I-270 just to the east. Immediately to the northeast, US 15 and US 340 have a folded diamond interchange with MD 180 and MD 351, which meets MD 180 just south of the interchange, that features four loop ramps. US 340 reaches its eastern terminus at the third interchange, which is a partial cloverleaf interchange with the Frederick Freeway. The first ramp from eastbound US 340 provides access to westbound I-70; the second ramp leads to the northbound Frederick Freeway (US 40), onto which US 15 exits. The ramps from westbound US 340 provide full access to I-70, I-270, US 15, and US 40. The roadway continues northeast as Jefferson Street, which reduces to a two-lane undivided street that heads toward an intersection with MD 144 (South Street eastbound and Patrick Street westbound) just west of downtown Frederick. The portion of Jefferson Street between the overpass of US 40 and just west of Jefferson Street's intersection with Pearl Street is unsigned US 15B.