There are seven primary sections of U.S. 20 in Iowa, as follows:
U.S. 20 and U.S. 75 run concurrently on a freeway bypassing Sioux City to the southeast. Immediately after U.S. 20 enters Iowa, it junctions Interstate 29. This junction is the eastern terminus of Interstate 129. At Gordon Drive, U.S. 20 leaves the freeway (U.S. 75 continues as a freeway or expressway to Le Mars) and enters an expressway alignment which continues to a point just east of Moville. There, U.S. 20 becomes a two-lane highway. It passes through Correctionville and is briefly concurrent with U.S. Route 59 as an expressway south of Holstein. Its north junction with U.S. Route 71 is three miles north of the small town of Early. The two roads run concurrently until a point two miles south of Early, where U.S. 20 turns east.
Just east of Moorland, U.S. 20 again becomes an expressway, running to the south of Fort Dodge. There are two full interchanges on this section, one at U.S. Route 169 and the other at Webster County Road P59 in Coalville. Otherwise, all intersections are at grade level.
Beginning at the junction of Iowa 17 on the Webster County/Hamilton County line near the unincorporated village of Flugstad, U.S. 20 becomes a full freeway and remains so throughout this entire section. U.S. 20 and Iowa 17 run together until Webster City, where Iowa 17 departs and turns south. U.S. 20 junctions Interstate 35 near Williams in eastern Hamilton County. It then junctions U.S. Route 65 south of Iowa Falls and Iowa Highway 14 south of Parkersburg, as well as a number of county roads along the way.
East of Iowa 14, U.S. 20 is a major bypass allowing through traffic to avoid passing through the cities of Cedar Falls and Waterloo. At the junction of Iowa Highway 58, U.S. 20 joins with Iowa Highway 27 and thus becomes part of the route of the Avenue of the Saints. U.S. 20 junctions U.S. Route 63 at Sergeant Road in Waterloo, then junctions Interstate 380 and U.S. Route 218 on the southeast side of Waterloo. U.S. 20, Iowa 27, and Interstate 380 run together approximately six miles to a point near Raymond, where Iowa 27 and Interstate 380 turn southeastward towards Cedar Rapids.
U.S. 20 continues as a freeway through this section. It junctions Iowa Highway 150 at Independence and Iowa Highway 13 at Manchester, as well as junctioning a number of county roads serving smaller communities.
At Delaware, U.S. 20 becomes an expressway once again, with at-grade intersections. However, there are still many interchanges where U.S. 20 meets major roads, mostly at the towns along U.S. 20's route. U.S. 20 serves Earlville, Dyersville (passing near the Field of Dreams filming site), Farley, Epworth, and Peosta before entering Dubuque. U.S. 20 remains at least four lanes through Dubuque, but there are several stoplights along the route, particularly on the western edge of the city. There is a brief controlled-access section where the highway descends into the Mississippi River valley. Near the river, a short connecting road connects U.S. 20 with U.S. Route 52, U.S. Route 61, and U.S. Route 151, which have entered the city from the south as an expressway and continue northward as a freeway. U.S. 20 crosses from Iowa into Illinois via the Julien Dubuque Bridge.
U.S. 20 was designated in Iowa on October 16, 1926. The designation created a single route number for drivers to follow across the state from Sioux City to Dubuque; previously, three route numbers were used.
The first segment of U.S. 20 in Iowa to become four lanes was a short expressway segment east of Moville, which opened in 1958. Another short expressway segment in the Dubuque area opened in 1959. The rest of the expressway from Sioux City to Moville opened in 1964. By 1979 the Sioux City bypass was complete, as well as the section from Iowa 17 to Interstate 35, and the section from Independence to Delaware. By the end of the 1980s, the four-lane portions of U.S. 20 ran from Coalville (near Fort Dodge) to Interstate 35 and from Waterloo to Dubuque.
During the 1990s little work was done to the route. It was extended westward to U.S. 169 in 1991, and eastward to U.S. 65 the same year, though initially the section from Interstate 35 to U.S. 65 was only two lanes. The new, semi-controlled section in Dubuque opened in 1996.
Work began to accelerate in 2000. The section between Interstate 35 and U.S. 65 became four lanes that year. The segment from Iowa 14 to Cedar Falls also opened in 2000. By 2003, the highway was complete from Fort Dodge to Dubuque.
It is possible to drive most of U.S. 20's former two-lane alignment from Moorland to Dubuque. Most of this routing (with the exception of Iowa Highway 57 from U.S. 65 to Cedar Falls) is now under city and county control, but most of the guide signs remain from when U.S. 20 followed this route. From Moorland, the highway's former alignment Business U.S. 20 through Fort Dodge. At County Road P59, it continues on County Road D20. The road changes designations several times between this point and Iowa Falls, but its route is very clear. It follows U.S. 65 north out of Iowa Falls to the junction of Iowa 57, then follows 57 to Cedar Falls. At Cedar Falls, the former alignment continues on U.S. 218 to Broadway Street; through Waterloo, it follows Broadway to Franklin Street to Dubuque Road. Beyond Waterloo the designation of the road again changes several times, but the route to follow remains clear. Between Dyersville and Farley U.S. 20 follows its historic alignment. At Farley, the former alignment follows Old Highway Road into Dubuque.
As of 2006, the state of Iowa is acquiring right of way to extend the U.S. 20 expressway westward from its current end at Moorland to a point 1.5 miles west of the current north junction with U.S. 71. Paving work is scheduled between Iowa Highway 4 and Moorland in 2010. However, it is expected that only two lanes of this segment will initially be paved, with the other two lanes to be paved at some later date. No work beyond right of way acquisition is scheduled on the segment between Iowa 4 and U.S. 71 as of October 2006.
West of U.S. 71, the remaining length of U.S. 20 (approximately 60 miles) faces an uncertain future. The state has stated its intention to finish the project, but has not formally committed to a completion date. Community leaders in the northwestern Iowa communities which would be served by a four-lane U.S. 20 continue to advocate for its completion, and impact studies are under way.
|Crossing the Missouri River from South Sioux City, Nebraska. See for exit list.|
|Woodbury||Sioux City||1||, South Sioux City||End of overlap with I-129.|
Signed as exits 1A (north) and 1B (south).
|4||End of overlap with US 75.|
Signed as exits 4A (east) and 4B (west).
|Ida||Holstein||West end of US 59 overlap.|
|East end of US 59 overlap.|
|Early||West end of US 71 overlap.|
|East end of US 71 overlap.|
|Calhoun||Rockwell City||West end of IA 4 overlap.|
|East end of IA 4 overlap.|
|Webster||Moorland||US 20 Business signed eastbound only|
|Coalville||Crossing the Des Moines River|
|124||US 20 Business signed westbound only|
|Hamilton||Webster City||136||West end of IA 17 overlap.|
|140||East end of IA 17 overlap.|
|Williams||153||Signed as exits 153A (south) and 153B (north)|
|Crossing the Iowa River|
|Milepost equation: 195 back = 208 ahead.|
|Cedar Falls||224||, University of Northern Iowa, UNI-Dome||West end of IA 58 overlap.|
|225||, Airport||East end of IA 58 overlap. West end of IA 27 overlap.|
|West end of I-380 overlap.|
Signed as exits 232A/71B (south) and 232B/71A (north)
|Evansdale||70||River Forest Road|
|68||Evansdale Drive – Elk Run Heights|
|East end of I-380 / IA 27 overlap.|
|Crossing the Wapsipinicon River|
|Peosta||308||, Northeast Iowa Community College|
|Grandview Avenue, Fremont Avenue|
|Hill Street, Bryant Street|
|Crossing the Mississippi River into East Dubuque, Illinois. See for exit list.|