Interstate 43

Interstate 43 (I-43) is a 191.55-mile (308.27 km) intrastate Interstate Highway located entirely within the U.S. state of Wisconsin, connecting Interstate 39 and Interstate 90 in Beloit with Milwaukee and U.S. Route 41 and U.S. Route 141 in Green Bay. I-43 is the 5th longest intrastate Interstate Highway of the Interstate Highway system. Wisconsin Highway 32 shares a concurrency with I-43 in two sections and US 41, U.S. Route 45, Interstate 94, Interstate 894, U.S. Route 10, Wisconsin Highway 57, and Wisconsin Highway 42 overlap I-43 once each. There are no auxiliary or business routes connected to I-43.

I-43 came about as a result of toll road proposals that included a Milwaukee to Superior corridor that included Hurley, Wausau and Green Bay. Only the Milwaukee to Green Bay section was approved. The route was originally planned to follow an alignment about midway between US 41 and US 141 (the latter paralleled Lake Michigan at the time) along Highway 57. Controversy about this location and use of right-of-way led to the establishment of the current alignment, which follows much of what was the 1950s-era realignment of US 141 from Milwaukee to Sheboygan, and a new alignment from Sheboygan to Green Bay. This section was completed in 1981.

The Beloit-to-Milwaukee segment was developed after two separate proposals for Interstates, one of them being between Milwaukee and Beloit and the other between Milwaukee and Janesville. The Milwaukee-Beloit route was chosen, completed in 1976 as WIS 15 and renumbered as I-43 in 1988. To connect the two segments, I-43 was signed concurrently with the east–west segment of I-894 and the north–south portion of I-94 in the greater Milwaukee metropolitan area from I-894 to the Marquette Interchange, which was completely reconstructed with work being completed in 2008.