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|direction_b=East |terminus_b= at McGregor |counties= |previous_type=IA |previous_route=17 |next_type=US |next_route=20 }} U.S. Highway 18 (US 18) is the northernmost east–west U.S. Highway in the state of Iowa. As with all state highways in Iowa, it is maintained by the Iowa Department of Transportation (Iowa DOT). It enters the state by crossing the Big Sioux River between Inwood and Canton, South Dakota. It travels and connects Spencer, Mason City and Charles City. The highway leaves the state via the Marquette–Joliet Bridge over the Mississippi River at Marquette. Prior to becoming a U.S. Highway, the route US 18 follows was known as Primary Road No. 19 and the National Parks Pike. ==Route description== US 18 begins at the Big Sioux River approximately east of Canton, South Dakota. It runs easterly through rural Lyon County, in the northwestern corner of the state. At Inwood it meets Iowa 182, which provides access to Sioux Falls, South Dakota, via Iowa 9 and South Dakota Highway 42. US 18 turns south at Inwood and heads into Sioux County. The highway crosses the Rock River on its way towards Rock Valley and Hull. West of Hull, at Perkins, US 18 juts to the south along US 75 before turning east again closer to Hull. The highway continues east towards Sheldon. As it crosses into O'Brien County on the western edge of Sheldon, US 18 intersects the business loop of Iowa 60. The two routes head east towards a diamond interchange with Iowa 60 on the eastern side of town where the business loop ends. The highway roughly parallels the Dakota, Minnesota and Eastern Railroad (DM&E Railroad). In Sanborn, US 18 is briefly overlapped by US 59, which joins from the north and leaves to the south. Continuing east, it passes through Hartley and then enters Clay County. North of Spencer, it intersects US 71 and the two routes head south together through town. On the south side of Spencer, the two routes come to a T intersection and each route heads in the opposite direction – US 18 to the east and US 71 to the west.〔 East of Spencer, US 18 passes through Ruthven in Palo Alto County. Between Ruthven and Emmetsburg, it is joined by Iowa 4 from the north. The two routes split again in Emmetsburg as Iowa 4 heads south. US 18 continues east, briefly heading south to enter Cylinder. The route curves back to the east at the DM&E Railroad line. An intersection with Iowa 15 near Whittemore marks the Palo Alto–Kossuth county line. Iowa 15 follows US 18 for before it splits away to the north. On the northern edge of Algona, the highway meets US 169. At the eastern county line, shared with Hancock County, is an intersection with Iowa 17, which marks that route's northern end.〔 In Hancock County, the route passes through Britt before meeting US 69 west of Garner; the two highways split in Garner. East of Garner, the route takes a north-northeasterly path as it goes through Ventura and skirts the northern shore of Clear Lake. Near the northeastern shore of the lake, it enters the city of Clear Lake, where it meets Interstate 35 (I-35). Iowa 122 and U.S. Route 18 Business (US 18 Bus.) head east from the interchange with the interstate. US 18 traffic follows southbound I-35 for . Iowa 27, the Avenue of the Saints highway, which had hitherto followed I-35 southbound now follows US 18 eastbound. The two routes, now on a four-lane, controlled-access highway, follow a path which passes to the south of Mason City. They meet US 65 and US 18 Bus. at exit 186.〔 At the Floyd county line, US and Iowa 27 become a limited-access road and angle slightly to the northeast, passing Rudd. At Floyd, the two routes are joined by US 218. The three routes head south along a bypass of Charles City. They intersect Iowa 14 on the western side of town and take a 90-degree curve to the east. At exit 218 of the expressway, US 18 leaves US 218 and Iowa 27, which continue southeastward towards Cedar Falls–Waterloo. US 18 briefly heads north into Charles City with US 218 Bus.. The two routes meet the northern end of Iowa 14, and US 18 splits away to the east to cross the Cedar River. Heading east again, the route enters Chickasaw County and passes through Bassett on its way to New Hampton. It meets US 63 at a four-lane bypass on the western side of town. The two routes head south for , splitting at the mile 196 interchange which is also the eastern end of Iowa 346. The route turns to travel due-east through Fredericksburg.〔 Continuing due-east, US 18 does not enter another community for until it reaches West Union in Fayette County. In West Union, it intersects Iowa 150. East of town, it crosses into the Driftless Area, an area that was untouched by glaciation during the last ice age. The route turns to the northeast to through Clermont and then to the north to meet US 52 at Postville in southern Allamakee County. The two routes head east through Postville and turn south into Clayton County. Near Froelich, US 52 leaves to the south towards Dubuque. Heading to the northeast towards, McGregor and Marquette, its business loop goes through the towns while the mainline skirts around them. The business loop rejoins the mainline at the foot of the Marquette–Joliet Bridge, which spans the Mississippi River.〔 US 18 continues east into Wisconsin with Wisconsin Highway 60, which begins at the state line.〔〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「U.S. Route 18 in Iowa」の詳細全文を読む スポンサード リンク
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