Local drivers will have a learning curve ahead of them when a new diverging diamond interchange at Milton Avenue and Interstate 90/39 opens as the I-90/39 reconstruction project between Beloit and Madison winds to a close.

People will also have to learn how to navigate new collector-distributor lanes that separate vehicles exiting and entering the Interstate from other Interstate traffic as it travels through the area around the highway 14 and 26 interchanges.

The two busy interchanges, located about a half-mile apart from each other on the city’s north end, will remain under heavy construction this spring, summer and part of fall with roadwork kicking into high gear starting early next week.

The work is part of the state Department of Transportation’s final push in the 45-mile-long lane expansion project that has gone on since 2015, and it is one of the project’s most complex aspects: the full replacement of the two interchanges that move an estimated 100,000 cars per day along I-90/39, Humes Road and Milton Avenue.

DOT Regional Communications Manager Steve Theisen said the Interstate and both interchanges are in line to reopen with a new configuration by mid-September. It will be the first time local drivers and commuters have seen the big highway fully open to traffic since work started.

But before that, motorists will once more run through a gantlet of roadwork along the heavily traveled nexus of roads. The work will require navigating unusual traffic patterns along Milton Avenue and, at times, on and off the Interstate at the two interchanges.

Starting Tuesday morning, people traveling along Highway 26 near the I-90/39 interchange should be ready for this monthslong change: The DOT plans to shift all Highway 26 traffic near the interchange to the northbound lanes of the highway.


Theisen said the shift will allow crews to begin work on new southbound lanes that will be part of the diverging diamond. That change will run through the end of June; at the end of July, Theisen said the DOT will shift Highway 26 traffic into the southbound lanes to do “mirror image” work on the northbound lanes. That shift will run through part of September, at which point the DOT is targeting completion of the Highway 26 interchange.

The end result will be a crossover traffic pattern similar to the diverging diamond design used at Highway 11’s junction with the Interstate on Janesville’s south end.

The DOT is implementing the diverging diamond because agency studies show the configuration improves traffic safety at interchanges that historically have a heavy volume of left-hand turns across traffic.

This spring and summer, the DOT plans to give advanced notice to motorists of temporary closures of ramps at Highway 26 as the interchange rebuild rolls out. One exit ramp closure has been ongoing and remains in effect.

Theisen said the southbound ramp off Highway 26 to the I-90/39 interchange, an exit that has been closed since August 2020, will remain closed until the end of August this year.

Another ramp at the same interchange, the northbound exit ramp to I-90/39, will close for about two weeks this summer.

That is in addition to the south exit ramp off I-90/39 onto Highway 26, which will see partial closure for six weeks.

During that closure, Theisen said, people will still be able to exit and head south onto Milton Avenue toward downtown Janesville, but they won’t be able to turn north on Highway 26 toward Milton.

Theisen said the DOT will announce all those closures ahead of time, and he said the DOT also will use marquee signs along the Interstate and Highway 26/Milton Avenue to help guide travelers through the construction zone.


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