Map of US highway 31 and family
US 31 is represented by the purple line from Mackinaw City MI to Spanish Fort AL (near Mobile). The red lines extending north and south of those points are the historic extents of US 31.
US 131 is the blue line from Petoskey to near White Pigeon MI.
US 231 is the blue line from St. John IN to Panama City FL.
US 331 [I] (historic) is the red line from Flomaton AL to Pensacola FL.
US 331 [II] is the blue line from Montgomery AL to Santa Rosa Beach FL.
US 431 is the green line from Owensboro KY to Dothan AL. (It's a regular 3-digit branch route, but I colored it green on this map in order to help differentiate it from US 231.)
