U.S. Route 18 in Iowa
# U.S. Route 18 in Iowa

U.S. Highway 18 (US 18) is the northernmost east–west United States Numbered 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 about 312 miles (502 km) 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 two miles (3.2 km) east of Canton, South Dakota. It runs easterly through rural Lyon County, in the northwestern corner of the state. At Inwood, it meets Iowa Highway 182 (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 toward 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 toward Sheldon.

As it crosses into O'Brien County on the western edge of Sheldon, US 18 intersects Iowa 60 Business (Iowa 60 Bus.). The two routes head east toward 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 one mile (1.6 km) 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 one mile (1.6 km) 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 US 18 Bus. head east from the interchange with the Interstate. US 18 traffic follows southbound I-35 for four miles (6.4 km). 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 18 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 toward 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 eight miles (13 km), 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 20 miles (32 km) 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 toward Dubuque. Heading to the northeast toward 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 State Trunk Highway 60, which begins at the state line.

## History

Before it and the rest of the U.S. Numbered Highway System were designated on November 11, 1926, US 18 was known by two names in the state. It was first known as Primary Road No. 19, which was assigned to the route when the Iowa State Highway Commission published its first state highway map in 1919. The route was also called the National Parks Pike, which began at Yellowstone National Park and ended in Madison, Wisconsin, encompassing all of Primary Road No. 19 in the state. The pike was registered with the on April 29, 1920. The National Parks Pike name fell into disuse after the highway became US 18.

By 1927, a significant portion of the route was paved, while the remainder was graveled. All of O'Brien County and 80 miles (130 km) between Algona and Charles City were paved. In seven years, the gap between O'Brien County and Algona was finished which created 160 miles (260 km) of continuous pavement. During those same seven years, the route from West Union to the Mississippi River and all of Primary Road No. 59, which included the seven-mile-long (11 km) overlap of US 18 near New Hampton were paved. Primary Road No. 59 is now known as US 63. By the start of World War II, the only remaining section of US 18 that was not paved was an 11-mile (18 km) section west of Rock Valley in Sioux County. That last section would not be completed for another 10 years.

Prior to 1932, the only way vehicles traveling US 18 could cross the Mississippi River was by ferry. That changed in when identical suspension bridges were built to cross the river between Marquette and Prairie du Chien, Wisconsin. Built in 1931–1932, each bridge was 450 feet (140 m) long, crossed a main channel of the river, and were divided by a 2,000-foot-long (610 m) island causeway. The first car to cross the bridges did so on March 7, 1932. Users of the bridge had to pay a toll until July 15, 1954. The bridges remained in use for another 20 years, when they were replaced by the Marquette–Joliet Bridge. In 1988–1989, a bypass was built around McGregor so US 18 could connect directly to the Marquette–Joliet Bridge. A short road had previously provided access to and from the bridge. The old alignment of the route became US 18 Bus.

Over the late 1990s, construction began on the Avenue of the Saints corridor near Mason City. A new controlled-access facility was built south of the city east to Rudd. On December 5, 1999, this section of freeway opened and US 18 was realigned onto the new road. The old alignment became Iowa 122. By the end of the next year, the four-lane expressway was extended to Charles City. By 2003, an expressway carrying US 63 was built around New Hampton. US 18 was rerouted onto the expressway and the western end of Iowa 24 was moved to the US 63/US 18 interchange.

## Major intersections

| County | Location | mi | km | Exit | Destinations | Notes |
| - | - | - | - | - | - | - |
| Big Sioux River | Big Sioux River | 0.000 | 0.000 | | US 18 west – Canton | Continuation into South Dakota |
| South Dakota–Iowa state line ||
| Lyon | Inwood | 4.992 | 8.034 | | Iowa 182 north to Iowa 9 | |
| Sioux | Lincoln Township | 24.853 | 39.997 | | US 75 north – Rock Rapids | Western end of US 75 overlap |
| Sioux | Lincoln Township | 25.848 | 41.598 | | US 75 south – Sioux Center | Eastern end of US 75 overlap |
| O'Brien | Sheldon | 42.184 | 67.889 | | Iowa 60 Business south (2nd Avenue) | Western end of Iowa 60 Business overlap |
| O'Brien | Sheldon | 44.269 | 71.244 | | Iowa 60 / Iowa 60 Business ends – Worthington, Minn., Sioux City | Eastern end of Iowa 60 Business overlap |
| O'Brien | Sanborn | 52.806 | 84.983 | | US 59 north – Worthington, Minn. | Western end of US 59 overlap |
| O'Brien | Franklin Township | 53.802 | 86.586 | | US 59 south – Primghar | Eastern end of US 59 overlap |
| Clay | Spencer | 77.770 | 125.159 | | US 71 north – Milford | Western end of US 71 overlap |
| Clay | Spencer | 81.755 | 131.572 | | US 71 south – Storm Lake | Eastern end of US 71 overlap |
| Palo Alto | Highland Township | 94.160 | 151.536 | | CR N20 – Ruthven | Former Iowa 341 |
| Palo Alto | Highland Township | 97.317 | 156.617 | | CR N28 – Ayrshire | Former Iowa 314 |
| Palo Alto | Emmetsburg Township | 101.306 | 163.036 | | Iowa 4 north – Graettinger | Western end of Iowa 4 overlap |
| Palo Alto | Emmetsburg | 106.075 | 170.711 | | Iowa 4 south (Broadway Street) – Pocahontas | Eastern end of Iowa 4 overlap |
| Palo Alto–Kossuth county line | Fern Valley–Fairfield– Lotts Creek–Whittemore township quadripoint | 119.698 | 192.635 | | Iowa 15 south – West Bend | Western end of Iowa 15 overlap |
| Kossuth | Lotts Creek–Whittemore township line | 120.687 | 194.227 | | Iowa 15 north – Fenton | Eastern end of Iowa 15 overlap |
| Kossuth | Algona | 130.144 | 209.446 | | US 169 – Algona, Bancroft | |
| Kossuth–Hancock county line | Wesley–Orthel township line | 143.858 | 231.517 | | Iowa 17 south – Corwith | |
| Hancock | Britt | 152.452 | 245.348 | | CR R35 – Crystal Lake, Kanawha | Former Iowa 111 |
| Hancock | Britt | 153.185 | 246.527 | | Diagonal Street | Former Iowa 424 |
| Hancock | Garfield Township | 160.877 | 258.906 | | US 69 north – Forest City | Western end of US 69 overlap |
| Hancock | Garner | 161.966 | 260.659 | | US 69 south – Belmond | Eastern end of US 69 overlap |
| Cerro Gordo | Clear Lake | 172.233 | 277.182 | | N. 8th Street | Former Iowa 107 |
| Cerro Gordo | Clear Lake | 175.352– 175.657 | 282.202– 282.693 | 194 | I-35 north / Iowa 27 north – Minneapolis US 18 Bus. east / Iowa 122 east – Mason City | Western end of I-35 / Iowa 27 overlap |
| Cerro Gordo | Clear Lake | 176.204 | 283.573 | 193 | CR B35 (4th Avenue South) | Former Iowa 106 |
| Cerro Gordo | Lake Township | 178.210– 179.045 | 286.801– 288.145 | 190 | I-35 south – Des Moines | Eastern end of I-35 overlap |
| Cerro Gordo | Lake Township | 183.163 | 294.772 | 183 | Eisenhower Avenue — Airport | |
| Cerro Gordo | Mason City | 186.409 | 299.996 | 186 | US 65 / US 18 Bus. west – Downtown Mason City, Rockwell | |
| Cerro Gordo | Portland Township | 190.460 | 306.516 | 190 | CR S56 (California Avenue) | |
| Cerro Gordo–Floyd county line | Portland–Rock Grove township line | 195.596 | 314.781 | 195 | CR S70 – Nora Springs | |
| Floyd | Rudd Township | 203.141 | 326.924 | | CR B30 – Rudd | Former US 18 |
| Floyd | Floyd | 210.282 | 338.416 | | US 218 north – Floyd, Osage | Northern end of US 218 overlap |
| Floyd | Floyd Township | 212.687 | 342.287 | 212 | US 218 Bus. / CR B35 – Charles City | |
| Floyd | Saint Charles Township | 214.811 | 345.705 | 214 | Iowa 14 – Charles City, Greene | |
| Floyd | Charles City | 218.023– 218.464 | 350.874– 351.584 | 218 | US 218 south / Iowa 27 south – Waterloo US 218 Bus. begins | Eastern end of US 218 and Iowa 27 overlaps; southern end of US 218 Business overlap |
| Floyd | Charles City | 219.311 | 352.947 | | Old Highway Road | Former US 218 |
| Floyd | Charles City | 220.238 | 354.439 | | US 218 Bus. north / Iowa 14 south | Northern end of US 218 Business overlap |
| Chickasaw | Chickasaw Township | 231.617 | 372.751 | | CR V14 – Ionia | Former Iowa 393 |
| Chickasaw | New Hampton | 237.701– 238.049 | 382.543– 383.103 | 204 | US 63 north / Iowa 24 east – New Hampton, Lime Springs | Western end of US 63 overlap |
| Chickasaw | New Hampton Township | 240.338 | 386.787 | 201 | 225th Street – New Hampton | |
| Chickasaw | Dresden Township | 244.457– 244.955 | 393.415– 394.217 | 196 | US 63 south / Iowa 346 west – Nashua, Waterloo | Eastern end of US 63 overlap |
| Fayette | Bethel Township | 258.905 | 416.667 | | CR V68 – Waucoma | Former Iowa 193 |
| Fayette | West Union | 270.469 | 435.278 | | Iowa 150 to Iowa 56 / River Bluffs Scenic Byway – Fayette, Calmar | Western end of River Bluffs Scenic Byway overlap |
| Fayette | West Union | | | | CR W42 / River Bluffs Scenic Byway | Eastern end of River Bluffs Scenic Byway overlap |
| Fayette | Clermont | | | | CR B40 / River Bluffs Scenic Byway | Western end of River Bluffs Scenic Byway overlap |
| Fayette | Clermont | | | | CR B60 / River Bluffs Scenic Byway | Eastern end of River Bluffs Scenic Byway overlap |
| Clayton | No major junctions | No major junctions | No major junctions | No major junctions | No major junctions | No major junctions |
| Allamakee | Post Township | 287.042 | 461.949 | | US 52 north – Calmar | Western end of US 52 overlap |
| Allamakee | Postville | 288.106 | 463.662 | | Iowa 51 north (N. Lawler Street) | |
| Allamakee | Postville | | | | CR B38 (S. Maple Street) / Driftless Area Scenic Byway | |
| Clayton | Giard Township | 303.396 | 488.269 | | US 52 south / River Bluffs Scenic Byway – Guttenberg | Eastern end of US 52 overlap; western end of River Bluffs Scenic Byway overlap |
| Clayton | Mendon Township | 307.864 | 495.459 | | US 18 Bus. east / Iowa 76 north – McGregor | |
| Clayton | Marquette | 311.613 | 501.493 | | US 18 Bus. west / Iowa 76 / Great River Road / River Bluffs Scenic Byway – Marquette, McGregor | |
| Mississippi River | Mississippi River | 311.750 | 501.713 | | Marquette–Joliet Bridge; Iowa–Wisconsin state line | Marquette–Joliet Bridge; Iowa–Wisconsin state line |
| Mississippi River | Mississippi River | 311.750 | 501.713 | | US 18 east / WIS 60 east – Prairie du Chien | Continuation into Wisconsin |
| 1.000 mi = 1.609 km; 1.000 km = 0.621 mi Concurrency terminus |||||||
