As a result, there are many historic sites along Alt US 40, including the Casselman Bridge in Grantsville and the last remaining National Road toll gate house in Maryland, located in LaVale.

[4] Alt US 40 runs from Keyser's Ridge to Cumberland, following part of the route of the National Road through some of Maryland's most mountainous terrain in Garrett and Allegany counties.

[4] It runs parallel to I-68 through northern Garrett County as a two-lane road with truck lanes on some uphill sections.

[6] A short distance east of this intersection, the highway meets MD 495, which junctions with I-68 and continues southward toward Oakland.

[8] East of Grantsville, Alt US 40 passes over the Casselman River on a steel bridge built in 1933.

East of Chestnut Ridge, the highway passes over Meadow Mountain at a height of 2,789 feet (850 m).

[6] Just east, the route crosses the larger Big Savage Mountain at an elevation of 2,847 feet (868 m) before entering Allegany County.

[11] After continuing into Allegany County, Alt US 40 descends Savage Mountain into Frostburg, where it passes through the town as Main Street.

[4] Continuing eastward from Frostburg, traffic density decreases, to an AADT of 13,585 at the MD 55 intersection, staying between 13,000 and 15,000 for the remainder of the highway.

[4] In the eastern part of Eckhart Mines, the highway intersects MD 743, which is an old alignment of US 40 which was bypassed by the roadway which became Alt US 40.

Near the MD 55 intersection is a stone arch bridge which was initially built in 1812 and rebuilt in the 1830s, and carried the National Road over Braddock Run, a tributary to Wills Creek.

[12] East of the intersection with MD 658, Alt US 40 turns northward, passing through LaVale toward the Narrows, bypassing Haystack Mountain to the north, as opposed to I-68, which passes directly over Haystack Mountain, paralleling Braddock Road (MD 49).

[4] Alt US 40 then passes through the Narrows, a gap between Haystack Mountain and Wills Mountain carved by Wills Creek, into Cumberland, where it follows Henderson Avenue and Baltimore Avenue to exit 44 on I-68, where Alt US 40 ends.

[4] The roadway which became Alt US 40 in Garrett and Allegany counties is, with some realignments, the route followed by the National Road through western Maryland.

[13] In 1755, during the French and Indian War, British troops under the command of General Edward Braddock completed the arduous task of building a road westward from Fort Cumberland.

They largely followed an Indian trail known as Nemacolin's Path, expanding it to a 12-foot-wide (3.7 m) road using only hand tools.

The road construction was part of the Braddock Expedition, which was the British campaign to seize Fort Duquesne from the French and Indian forces.

[7] Many sites from the National Road remain along Alt US 40, in particular the LaVale toll gate house, built in 1836.

[18] Another realignment of Alt US 40 occurred in Eckhart Mines, where in 1969 the road, then designated as US 40, was realigned to the north, bypassing the section of the highway through Eckhart Mines, which has a lower speed limit and sharp curves.

[13] The stone arch bridge, located just south of the current alignment of Alt US 40, was restored in 1976.

[21] The portions of US 40 that were bypassed between Cumberland and Keysers Ridge became U.S. Route 40 Alternate, which first appeared on MDSHA maps in the early 1980s.