U.S. Route 231 in Indiana  U.S. Route 231 (US 231) in Indiana is a main north–south highway in the western part of the state. The southern terminus of US 231 is at the Kentucky state line and the northern terminus is at US 41 just south of St. John. The highway is a mixture of expressway and two-lane roadway. The expressway is mainly in southern Indiana and around the Lafayette area, with the rest mainly being two-lanes. US 231 was initially signed as a state road from Spencer to Lafayette. North of Lafayette, the road was a U.S. Highway until it was decommissioned in favor of US 231. This route will become an expressway in southern Indiana from the current northern terminus of the expressway to the future interchange at Interstate 69 (I–69). US 231 contains two segments included as a part of the National Highway System (NHS). The first segment runs from the Kentucky state line to SR 558 and the second segment runs from I-70 to Lafayette. The highway is maintained by the Indiana Department of Transportation (INDOT) like all other U.S. Highways in the state. The department tracks the traffic volumes along all state highways as a part of its maintenance responsibilities using a metric called average annual daily traffic (AADT). This measurement is a calculation of the traffic level along a segment of roadway for any day of the year. In 2010, INDOT calculated that the section of US 231 with the lowest average daily traffic levels – with 1,100 vehicles and 180 commercial vehicles – was from US 52 to I–65. The peak traffic volumes on US 231 was 27,990 vehicles and 1,950 commercial vehicles AADT along the section concurrent with US 52. US 231 enters Indiana on the William H. Natcher Bridge over the Ohio River from Kentucky. The road enters as a four–lane divided highway and immediately has a folded diamond interchange with State Road 66 (SR 66). The highway heads north passing a power plant and through farmland towards Dale; the expressway then intersects with SR 70. The route turns northeast, passing through woods, just south of Lincoln State Park. The road turns north having an interchange with SR 162; this exit allows access to the State Park. The expressway then turns northwest and enters Dale. On the south side of Dale, the roadway intersects SR 62; this is the old route of US 231.