Vermont Route 18 begins at the New Hampshire state line between Littleton and Waterford. After crossing the Connecticut River into Vermont, VT 18 veers westward to cross under I-93 into Lower Waterford village. VT 18 then continues northwest running closely parallel to I-93 on its west side for roughly 7 miles (11 km) until Stiles Pond. Just north of the pond, I-93 changes direction from northwest to southwest. VT 18 crosses under I-93 at this point with an interchange at Exit 1, where US 2 Truck joins VT 18 for a short concurrency. Soon after junction with I-93, which is the only numbered exit on that route in Vermont, VT 18 and US 2 Truck end at U.S. Route 2 about 0.25 miles (0.40 km) past the St. Johnsbury town line. US 2 continues into the town center. VT 18 is part of the Connecticut River Byway.[3]
In late 1926, the U.S. Highway system was established. U.S. Route 2 in Vermont was designated on New England Route 14 (Burlington to Montpelier), New England Route 25 (Montpelier to Wells River) and New England Route 15 (St. Johnsbury to Lunenburg), connected by a brief overlap with U.S. Route 5.[7][8] In 1935, the portion of U.S. Route 2 between Montpelier and St. Johnsbury was relocated to use the alignment of Vermont Route 18. The previous alignment from Montpelier to Wells River was designated as part of newly established U.S. Route 302,[citation needed] and the overlap with U.S. Route 5 was eliminated.[9] This truncated the northern/western end of Vermont Route 18 to St. Johnsbury.[9]
^Max J. Skidmore, Moose Crossing: Portland to Portland on the Theodore Roosevelt International Highway, Hamilton Books, 2006, ISBN0-7618-3510-5
^Official Automobile Blue Book, Vol. 1, 1926 edition, (Automobile Blue Books Inc., Chicago, 1926). Map indicated the routing of the Theodore Roosevelt International Highway by "T" markers along the route.
^Automobile Legal Association Green Book, 1925 edition, (Scarborough Motor Guide Co., Boston, 1925). A route log of the New England Inter-state routes is included in the book showing rough mileage.