List of auto trails in Maine

Auto trails in Maine
Maine's early highway system
System information
Maintained by MaineDOT
Highway names
Interstates	Interstate x (abbreviated I-X)
US Highways	U.S. Route x (abbreviated US-X)
State	State Route x or Route x (abbreviated SR X)
Lettered routes	Route x
System links
Maine State Highway System Interstate US State Auto trails Lettered highways

Beginning in 1914, Maine used a system of lettered highways to designate cross-state routes; however, these were internal designations, never meant to be signed for use by drivers. In 1919, the Maine Automobile Association and the Maine State Highway Commission collaborated to create a series of state-designated auto trails specifically to aid public navigation. 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. This system was abandoned by 1925 in favor of the New England interstate highway system.

List

It is unclear which routes listed below existed at what times.

Route	Colors	From	Through	To	Lettered route	Replacement (1925)	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 (Québec) 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, (24)	US 2, (US 1)	1923: Extended to Houlton, then Mars Hill, Presque Isle, Caribou, Van Buren, Madawaska to Canada (New Brunswick) 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