The Zoo Freeway, opened to traffic between County Trunk Highway T (Beloit Road) and Interstate 94 in 1963. The remainder of the freeway south to the Hale Interchange (I-43 / old Wis 15) and east to the Mitchell Interchange (I-94) followed in 1966. Interstate 43 was extended southwest via the former Wis 15 freeway toward Beloit officially on November 24, 1987, with signage erected in the following year.1
Escalating construction costs in 2003 associated with the massive rebuild of the Marquette Interchange in Downtown Milwaukee, where I-43, I-94 and I-794 converge, included several cost cutting ideas touted by then major John Norquist. A scaled down interchange revamp developed by city engineers would save $361 million by only moving one of the left-hand ramps at the busy Downtown junction. Coupled with that was a renumbering plan proposed by the mayor that might offset traffic through the exchange. The plan included rerouting I-94 over all of Interstate 894, extending I-794 west from the Marquette Interchange to the Zoo Interchange over former I-94, and leaving the North-South Freeway as simply I-43.2 This proposed renumbering was never implemented and the Marquette Interchange was ultimately rebuilt between 2005 and December 2008.
Major construction redesigned the Mitchell Interchange over the course of four years as part of a $300 million project. The work eliminated left exit ramps along Interstate 94 while reconfiguring the adjacent interchange with S 27th Street (Exit 9) to offset weaving traffic patterns along I-43/894. Project elements included 51 bridges, three tunnels and more than 17 sound walls. A ribbon cutting ceremony marked the end of construction on November 9, 2012, with work completed a month and a half ahead of schedule.3
Interstate 41 was approved by AASHTO on November 15, 2012. Signs for the route were erected starting in May 2015. The designation replaces the entirety of U.S. 41 between Rosecrans, Illinois and Green Bay, Wisconsin. I-41 overlays all of I-894, but there are no plans to decommission the 894 designation due to its role as a through route bypass for I-94. The three way overlap between I-41, I-43 and I-894 along the Airport Freeway results in a “wrong way” overlap where I-41 north travels along side I-43 south and vice versa.