U.S. Route 231 (US 231) is the longest numbered highway in Indiana, covering over . It 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 portions exist mainly in southern Indiana and around the Lafayette area, with the rest mainly being two lanes.
Route description
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.
Southern Indiana
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 large, coal fired power plant (Rockport Generating Station) and through farmland towards Chrisney; 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, as well as the Holiday World & Splashin' Safari theme park, a few miles to the east.
The expressway then turns northwest and skirts the south and west sides of Dale. On the south side of town, the roadway intersects SR 62; this is the old route of US 231, which joins the expressway for a brief period before turning east at the junction with SR 68. I–64 is a little more than a mile north from this point, with its interchange just south of the end of the expressway.
U.S. 231 enters Dubois County, crossing into the Eastern Time Zone. From this point northward through the remainder of Southern Indiana, the highway will remain mostly a rural two-lane road.
US 231 heads towards Huntingburg, passing through rural farmland. The highway enters Huntingburg from the south, passing through residential areas. The route has a traffic light in downtown Huntingburg with SR 64. North of downtown Huntingburg, the road passes through commercial properties, before leaving town. The highway then heads north towards Jasper, passing by a mix of both farmland and woodland. US 231 enters Jasper from the south, passing by commercial lots. West of downtown Jasper, the route begins a concurrency with SR 56, with both routes heading east. The concurrency enters downtown and has a traffic light at the northern terminus of SR 164. That is intersection US 231 and SR 56 turn towards the north. The two highways head north into residential areas. The road leaves Jasper heading northeastward toward Loogootee. In Haysville, the concurrency with SR 56 ends. US 231 heads north-northeast from SR 54, before turning more northward. The highway enters Loogootee and begins a concurrency with both U.S. Route 50 (US 50) and US 150. The concurrency travels due north, then turns northeast and enters downtown Loogootee. In downtown, the concurrency ends, with US 50 and US 150 heading east and US 231 heading northwest. The highway then heads north towards Bloomfield, passing the Naval Surface Warfare Center Crane Division.