I-39 south / I-90 east separate with Interstate 94 on the east side of Madison, Wisconsin. I-94 bee lines for Milwaukee while I-39/90 remain paired south to Beloit and Rockford, Illinois. 05/30/11
Interstate 39 runs north-south through Illinois and Wisconsin as a long distance bypass for traffic around the Chicago and Milwaukee metropolitan areas. A mostly rural route, I-39 begins on the north side of Normal at I-55, overtaking U.S. 51 to Peru and La Salle, where it meets Interstate 80. North from there, the freeway continues to I-88 outside Rochelle and U.S. 20 on the south side of Rockford.
U.S. 20 turns the freeway east to Interstate 90, the Jane Addams Memorial (Northwest) Tollway. I-39/90 combine there along the east side of Rockford to Beloit, Wisconsin, where they meet the south end of Interstate 43. Advancing northward, the pair pass through Janesville while en route to the capital city of Madison. There Interstate 94 ties in from Waukesha and Milwaukee to the east to form the longest three-way overlap on the Interstate system.
I-39, I-90 and I-94 run concurrently for 29 miles along a northward heading from Madison to the outskirts of Portage. I-39 separates with I-90/94 just beyond the Wisconsin River to again overtake U.S. 51 northward from Portage to Packawaukee, Plover and Stevens Point.
U.S. 10 combines with I-39/U.S. 51 from Stevens Point to a August 2012-completed freeway leading west to Junction City and Milladore. U.S. 51 otherwise parallels the Wisconsin River north to Mosinee, Rothschild and its terminus at the south junction of U.S. 51 and Wis 29. U.S. 51 extends the freeway north along side Wis 29 to Wausau and as a solo route northward to Merrill.
A long term project underway in south central Wisconsin, the I-39/90 Expansion Project, affects 45 miles of the I-39/90 overlap from the Illinois state line to U.S. 12/18 at Madison. The 1960s-era freeway includes 11 interchanges with elements of substandard design. Upgrades to the corridor include expansion of the freeway mainline to six overall lanes, reconfiguring the aforementioned interchanges, and additional expansion of I-39/90 to eight lanes between Wis 11 (Avalon Road) north to Wis 26. Construction runs from 2015 to 2023.
The conversion of Exit 177 with Wis (Avalon Road) to a diverging diamond interchange will be the first DDI in the state. The South Segment at Beloit, a major upgrade started in Summer 2019 at exchange joining I-39/90 with the south end of Interstate 43 and Wis 81. Work through Fall 2021 converts the previous cloverleaf interchange into a semi/directional T for freeway to freeway movements and a DDI for Wis 81 leading west into Beloit.