This new freeway corridor became an Interstate Corridor as a result of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) legislation (signed into law on August 10, 2005). This legislation not only added U.S. 41 between Milwaukee and Green Bay as High Priority Corridor 57, it also designated Corridor 57 as a future Interstate route. An earlier version of this law (HR 3, Section 1839) had language that indicated that High Priority Corridor 57 “is designated as Interstate Route I-41.” However, SAFETEA-LU does not have a similar provision that specifies the route number for the future Interstate to be routed over U.S. 41.2
Numbers discussed by WisDOT included I-47, I-243, I-594 and I-643 in addition to Interstate 41. The selections went to American Association of State Highway and Transportation Officials (AASHTO) and at their meeting on November 15, 2012 an endorsement of the number “41” was given for the future Interstate highway. The numbering moved to the Federal Highway Administration for approval before Interstate 41 was made official.3
A WisDOT map of the US 41 Conversion showed the proposal to extend Interstate 41 southward along all of Interstate 894 and I-94 south from Milwaukee to the first exit in Illinois.3 Logic behind this overlap retained mileposts and exit numbers along the preexisting U.S. 41 freeway between Milwaukee and Green Bay.
The non-freeway portion of U.S. 41 along Appleton Avenue from the Stadium Freeway/Miller Park Way northwest to I-41 at Exit 47 near Menonmonee Falls was renumbered as an extension of WIS 175.
Two projects along Interstate 41 and U.S. 41 involved upgrading the freeway through Brown and Winnebago Counties. The Brown County work involved a 14-mile stretch from Orange Lane to Lineville Road (CTH-M). Construction commenced in 2010 and was completed in 2017. Elements of work included rebuilding nine interchanges, adding 24 roundabouts and widening the freeway from four to six and ten overall lanes. More details are as follows:
- Lineville Road (County Trunk Highway M) interchange – work completed from June 2013 to May 2015.
I-41 was expanded to six lanes below a new overpass for CTH M while ramps were expanded to two lanes.
- I-41 and I-43 Interchange – work started in September 2013 and ran through December 2016. The new northbound ramp from I-43 to I-41 opened on July 27, 2015. Following was opening of the new I-41 north to I-43 south flyover opened on August 28, 2015. The new flyover from I-43 north to I-41 south opened on August 26, 2016.
Construction replaced all loop ramps with directional ramps as part of new directional T interchange. Adjacent work separated movements to Velp Avenue (U.S. 141) and eliminated weaving traffic to and from I-43.
- Packerland Drive – WIS 29 Interchange – work completed in early 2015 included construction to add flyovers from and to WIS 29/32 leading west from I-41/U.S. 41. The new directional T overlays a diamond interchange with roundabouts at Shawano Avenue.
- WIS 172 Ramps – construction started in Fall 2013 and concluded in Fall 2016.
Ramps were expanded and realigned to join new collector distributor lanes along Interstate 41.
Work in Winnebago County affected 17 miles of I-41/U.S. 41 from WIS 26 to Breezewood Lane. Construction was completed between 2009 and 2014. Upgrades included a new eight lane Lake Butte des Morts Causeway, reconstruction of four interchanges, and the addition of 16 roundabouts. Of this work, the interchange with U.S. 45 received a substantial makeover with free flow movements added from north I-41 to north U.S. 45 and from U.S. 45 south to I-41 south.