passes above Chesapeake and Ohio Canal National Historical Park, CSX's Cumberland Subdivision rail line, and Sandy Hook Road. US 340 expands to a four-lane freeway at the community of Sandy Hook, curves east through a trumpet interchange with MD 67 (Rohrersville Road), and crosses Israel Creek at Weverton. The highway, the canal, and the railroad parallel the Potomac River through the second ridge, which comprises South Mountain in Maryland and Short Hill Mountain in Virginia. US 340's name changes to Jefferson National Pike as it enters Frederick County. The highway leaves the Potomac Water Gap and enters the Middletown Valley at its partial interchange with MD 180 (Jefferson Pike) at Knoxville; there is no access from westbound US 340 to eastbound MD 180 or from westbound MD 180 to eastbound US 340. 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. 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 concurrent highways' next interchange, a diamond interchange with Mt. Zion Road. US 340 and US 15 cross over Ballenger Creek before reaching a diamond interchange with Jefferson Technology Parkway, which is unsigned MD 872G. 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 340 and US 15 have a four-loop-ramp interchange with MD 180, which heads west as Jefferson Pike and south briefly as Ballenger Creek Pike. 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