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. RouteColorsFromThroughToLettered routeReplacement (1925)Modern designationNotesAtlantic HighwayBlueNew Hampshire LineKittery, Wells, Kennebunk, Scarborough, Portland, Yarmouth, Brunswick, Bath, Wiscasset, Waldoboro, Rockland, Belfast, Searsport, Bangor, Ellsworth, Hancock, Millbridge, Jonesboro, Machias, Dennysville, Perry, RobbinstonCalaisA, C, D, L, M, NRoute 1US 1Longfellow HighwayYellowNew Hampshire LineBethel, Bryant Pond, West Paris, South Paris, Norway, Poland, GrayPortlandO, SRoute 15US 2, SR 26Theodore Roosevelt International HighwayWhite Red
WhiteNew Hampshire LineFryeburg, Bridgton, Naples, Raymond, North Windham, Highland LakePortlandBRoute 18U.S. 302Grafton Notch HighwayWhite YellowNew Hampshire LineUpton, NewryBethelT, ORoute 26US 2International TrailRedBrunswickGardiner, Augusta, Waterville, Skowhegan, Norridgewock, Anson, Solon, Caratunk Plt, Jackman StationCanada (Québec) LineQ, HRoute 20U.S. 201, U.S. 201AAroostock TrailWhite BlueFairfieldClinton, Pittsfield, Newport, Bangor, Old TownLincolnI, KRoute 100, 15, (24)US 2, (US 1)1923: Extended to Houlton, then Mars Hill, Presque Isle, Caribou, Van Buren, Madawaska to Canada (New Brunswick) LineCapital WayBlue WhitePortlandLewistonAugustaERoute 100SR 100, US 202Kennebec-Penobscot TrailOrange WhiteAugustaSouth China, Liberty, Searsmont, BelmontBelfastRRoute 102US 202, SR 3Mount Desert TrailYellow WhiteEllsworthHulls CoveBar HarborMRoute 183SR 183, SR 3Brunswick-Greenville HighwayGreen WhiteNewportDexter, Dover, Guilford, Abbott, MonsonGreenvilleJRoute 104SR 7, SR 23, SR 6Poland Springs-White Mountain TrailGreenNaplesCasco, PolandMechanic's FallsRoute 116SR 111
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