List of auto trails in Maine

Maine was one of the first states to mark their state highway system. From 1914 to 1925, Maine used a system of lettered highways to designate cross-state routes. This system was the first of its kind in the United States coordinated by a single state, predating Wisconsin's system by three years. In 1919, this system was supplanted by a series of auto trails officially created by the State Highway Commission, though it is unclear as to whether this system completely supplanted the lettering system. Both systems were abandoned by 1925 in favor of the New England interstate highway system.

List

In 1919, the Maine Automobile Association and the Maine State Highway Commission collaborated to create a series of state-designated auto trails. The system posed a stark contrast to the auto trail systems of other states, which were often private endeavors, with improvements by these booster organizations ranging from simple marked poles to paving and maintenance of the road. It is unclear which routes listed below existed at what times.

Route	Colors	From	Through	To	Lettered route	Replacement	Modern designation	Notes
Atlantic Highway	Blue	New Hampshire Line	Kittery, Wells, Kennebunk, Scarborough, Portland, Yarmouth, Brunswick, Bath, Wiscasset, Waldoboro, Rockland, Belfast, Searsport, Bangor, Ellsworth, Hancock, Millbridge, Jonesboro, Machias, Dennysville, Perry, Robbinston	Calais	A, C, D, L, M, N	Route 1	US 1
Longfellow Highway	Yellow	New Hampshire Line	Bethel, Bryant Pond, West Paris, South Paris, Norway, Poland, Gray	Portland	O, S	Route 15	US 2, SR 26
Theodore Roosevelt International Highway	White Red White	New Hampshire Line	Fryeburg, Bridgton, Naples, Raymond, North Windham, Highland Lake	Portland	B	Route 18	U.S. 302
Grafton Notch Highway	White Yellow	New Hampshire Line	Upton, Newry	Bethel	T, O	Route 26	US 2
International Trail	Red	Brunswick	Gardiner, Augusta, Waterville, Skowhegan, Norridgewock, Anson, Solon, Caratunk Plt, Jackman Station	Canada Line	Q, H	Route 20	U.S. 201, U.S. 201A
Aroostock Trail	White Blue	Fairfield	Clinton, Pittsfield, Newport, Bangor, Old Town	Lincoln	I, K	Route 100, 15,	US 2,	1923: Extended to Houlton, then Mars Hill, Presque Isle, Caribou, Van Buren, Madawaska to Canada Line
Capital Way	Blue White	Portland	Lewiston	Augusta	E	Route 100	SR 100, US 202
Kennebec-Penobscot Trail	Orange White	Augusta	South China, Liberty, Searsmont, Belmont	Belfast	R	Route 102	US 202, SR 3
Mount Desert Trail	Yellow White	Ellsworth	Hulls Cove	Bar Harbor	M	Route 183	SR 183, SR 3
Brunswick-Greenville Highway	Green White	Newport	Dexter, Dover, Guilford, Abbott, Monson	Greenville	J	Route 104	SR 7, SR 23, SR 6
Poland Springs-White Mountain Trail	Green	Naples	Casco, Poland	Mechanic's Falls		Route 116	SR 111