Alabama State Route 3

U.S. Route 31
Route information
Length:	1,280 mi (2,060 km)
Existed:	November 11, 1926 (1926-11-11) – present
Major junctions
South end:	US 90 / US 98 in Spanish Fort, AL
	I‑20 / I‑59 at Birmingham, AL I‑22 near Fultondale, AL I‑24 in Nashville, TN I‑40 in Nashville, TN I‑64 in Louisville, KY I‑70 / I‑74 at Indianapolis, IN I‑80 / I‑90 at South Bend, IN I‑94 near Benton Harbor, MI I‑96 near Muskegon, MI
North end:	I-75 in Mackinaw City, MI
Location
States:	Alabama, Tennessee, Kentucky, Indiana, Michigan
Highway system
United States Numbered Highway System List Special Divided Replaced

U.S. Route 31 or U.S. Highway 31 (US 31) is a long north–south highway connecting southern Alabama to northern Michigan. Its southern terminus is at an intersection with US 90/US 98 in Spanish Fort, Alabama. Its northern terminus is at an interchange with Interstate 75 (I-75) south of Mackinaw City, Michigan.

US 31 once crossed the Straits of Mackinac by car ferry to intersect US 2 north of St. Ignace, Michigan, in the Upper Peninsula and then formerly reached Mackinaw City along the southern approaches of the Mackinac Bridge (which has been taken over by I-75). It also formerly entered downtown Mobile, Alabama, via a long bridge over Mobile Bay.

US 31 begins in Spanish Fort, Alabama at a junction with US 90 and 98. Formerly, the route originated in Mobile, co-routed with US 90 and 98. Whereas Interstate 65 leaves the Mobile Metropolitan Area via a route on the west side of the city, US 31 leaves the Mobile area via a route on the eastern side of the metro area, passing through Bay Minette. I-65 has effectively replaced US 31 as the preferred route for through traffic, making US 31 a local connecting route.

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Wikipedia