Interstate 43 connects the Milwaukee area with Beloit to the southwest and Green Bay to the north. Following the Rock Freeway, I-43 originates at I-39/90 and angles northeast from Beloit to Delavan, Elkhorn, Mukwonago and the southwestern Milwaukee suburbs. Once at the Hale Interchange with Interstates 41 and 894 in Greenfield, I-43 joins the Airport Freeway east to south Milwaukee and the Airport Interchange with I-94.
Combining with Interstate 94 (North South Freeway), I-43 turns north through the Saveland Park and Walker’s Point neighborhoods of Milwaukee to the Marquette Interchange with the East West Freeway. There I-94 turns west through Menomonee River Valley while I-794 spurs east to Downtown and the Historic Third Ward. Interstate 43 meanwhile remains along the North South Freeway to Kilbourn Town, Harambee and an exit of Milwaukee at Grover Heights.
The urban style freeway of I-43 advances north through Glendale along an expressway originally built for U.S. 141. Continuing through the northern suburb villages of Fox Point, River Hills and Bayside, Interstate 43 leaves the Milwaukee area for Saukville and the split with Wis 57. There the freeway turns east by Port Washington to run along the west shore of Lake Michigan to Sheboygan and Manitowoc.
View of Leo Frigo Bridge from mouth of Fox River Photo by Peter Johnson (06/17/15).
The rural freeway leads away from the lake through northern Manitowoc County to enter Brown County and the Green Bay metropolitan area. Once at Bellevue, I-43 curves northeast than west as part a belt route with Wis 172 and I-41 encircling Green Bay. The final stretch traverses industrial and wetland areas along the southern periphery of Green Bay itself, including the high level Leo Frigo Bridge across the Fox River.
Interstate 43 replaced U.S. 141 between Milwaukee and Green Bay. The route also doubles as U.S. 41 along the south leg of I-41/894 in Milwaukee.
Interstate 43 was not an original 1956 Interstate Highway; it was commissioned in the 1970s along U.S. 141 as part of the Milwaukee-Green Bay Interstate Highway.1 Government planning maps of the Interstate Highway System from that era initially showed Interstate 43 as part of an extended Interstate 57, with presumably a long overlap along Interstate 94 from Chicago to Milwaukee (note that this overlap was never shown on any planning maps, so it would have been implied). Potential funding for the freeway in 1972 referenced the future Interstate as an extension of I-57 as well.2
The initial 82 mile long route for I-57 was approved by the Federal Highway Administration in May 1973 from Saukville, northeast along U.S. 141, to Wis 42 at Sheboygan and then northward to U.S. 151 outside Manitowoc. A northwesterly trajectory took I-57 from U.S. 151 to the planned Bellevue interchange south of Green Bay. This route did not extend south of Saukville due to the controversial Cedarburg Bog area. Instead provisions were made to tie the new I-57 in with the preexisting U.S. 141 freeway south of Saukville. The proposed new I-57 took it through Mequon and along the Wisconsin 57 corridor into Milwaukee otherwise.3
The Milwaukee-Green Bay Interstate was soon designated as a distinct route (numbered Interstate 43) and the southern terminus was located at the current junction between Interstates 94 and 794 (Marquette Interchange) in Downtown Milwaukee. The existing U.S. 141 freeway in north Milwaukee became part of I-43; the Interstate was then extended north toward Green Bay. Construction of this portion of the route was completed in 1981.1
Further south, what was originally designated as Wis 15 (via the Rock Freeway, which connected Beloit with Milwaukee) began construction in 1969 and was completed in 1976. Approximately ten years later on November 24, 1987, the highway was added to Interstate 43. With this action, I-43 gained 72 miles to the southwest along Wis 15 (Rock Freeway) to Interstate 90 near the state line.1 STH-15 was decommissioned by this action. With the extension of Interstate 39 into Wisconsin on October 16, 1992, I-43 connected to I-39. Signs for Interstate 39 were mostly erected around 1996.
For more information, visit Chris Bessert’s Wisconsin Highways: Interstate 43 page. This page also includes a discussion of the proposed location of the “Milwaukee to Green Bay Interstate Highway,” including consideration for what later became Interstate 41 as a candidate for I-43 in the early planning stages.