'Zipper merge' set to end by Thanksgiving

State transportation officials are shooting for the "zipper merge" to come down in time for Thanksgiving.

Project managers said about a month of construction remains before they can reopen a lane of eastbound I-94 traffic at the Zoo Interchange construction project. To funnel traffic from three lanes to two, officials instituted what's commonly known as a "zipper merge," causing traffic backups west of the interchange.

The "zipper merge" lane has been closed as about $300 million worth of work — known as Phase 2 of the Zoo Interchange project — is done on the highway and areas west of the interchange. Transportation officials originally said they were planning to open the lane of traffic in the fall, though at one point they thought the work could be completed by Aug. 1.

"We still have a chance to ultimately maintain our commitment to the public," said Brett Wallace, director of system development for the department's Southeast Region.

In its original contract with Chicago-based Walsh Construction Co., plans called for the "zipper merge" to come down in the fall. The contract was amended in March, moving up the required finish date to August. Wallace said workers were able to gain access to the construction site earlier than expected, and a tweak in construction plans reduced the expected time to complete the section of highway.

But an issue came up. Engineers grew worried that large, underground sewer pipes wouldn't be able to handle the pressure placed on them by the new highway. So for a few months, engineers debated whether they should reinforce the pipes, DOT officials said.

"When you're putting a brand-new interstate on top of (the pipes), you've got one chance to make sure you've got it right," said Ryan Luck, the Zoo Interchange's construction chief.

Ultimately, officials settled on installing a liner inside the pipes, which required digging about 20 feet underground and pulling up 1,200 feet of 8-foot-diameter concrete piping. The decision added about $4 million to the project's cost, and it took the August deadline off the table.

In early June, Walsh Construction Co.'s contract was again amended, giving the company until mid-December to reopen traffic.

Luck said the Phase 2 portion of construction remains under budget. The DOT includes contingency costs in the budget, with a goal of keeping them below 5%.   For Phase 2, that meant about $15 million in contingency costs, about $10 million of which have been used.

The core of the project, which includes all work near the interchange, is on track to be completed by the fall of 2018.

The final portion of construction — on U.S. 45, between W. Watertown Plank Road and W. Burleigh St. — is scheduled to be done by 2020. But under a DOT budget proposal issued earlier this month, that work would be delayed to 2022. Gov. Scott Walker is supporting the proposal, saying it would help him uphold his promise to not raise state taxes and fees.

"We're going to do everything that we can to fulfill our commitment to the public and get the core Zoo Interchange done and completed by fall of 2018," Wallace said. "The piece (of U.S. 45) north of Watertown Plank, there's been some changes in the schedule. But again, that's just part of the legislative process and figuring out how to pay for an awful lot of work."