The Toledo-area’s second major freeway detour in as many days starts Tuesday when northbound I-75 closes within the I-280 junction in North Toledo for replacement of two bridges.

About 47,000 vehicles each day will be affected by the shutdown, which was not part of the Ohio Department of Transportation’s original plan for rebuilding and widening I-75 between I-280 and the I-475 junction in central Toledo.

State officials decided early this spring that closing northbound I-75 was their best alternative when unexpectedly wet soil beneath the two bridges thwarted the original plan to rebuild them while maintaining lanes for traffic.

Two lanes of traffic will be maintained on a fairly short detour route, but traffic is likely to back up because of sharp curves.

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“We know the traffic is going to slow down, although that may also make it safer,” said Todd Audet, ODOT’s district deputy director in Bowling Green.

During the shutdown, the northbound I-75 bridges over ramps linking southbound I-75 with I-280 will be torn down and replaced with much wider spans that will carry both sides of I-75 when they’re finished.

All traffic on northbound I-75 will be forced onto southbound I-280 as far as Central Avenue, where temporary ramps will provide a turnaround, for about seven months.

Southbound I-75 will not be affected.

The North Toledo detour follows by one day today’s closing of two ramps at the I-75 junction with I-475/​U.S. 23 in Perrysburg: the northbound I-75 exit to northbound I-475/​U.S. 23, and the northbound I-75 entrance from southbound I-475/​U.S. 23.

Compared with the detours for those ramp closings, which were a planned part of I-75 reconstruction in Wood County, the North Toledo detour route is short: only about 1½ miles down I-280 to Central and back.

But curves on the ramps at Central will be posted for 25 mph, so backups are likely at least during rush hours, if not longer during the day, and especially when truck traffic is heavy.

The worst traffic jams are likely Tuesday, when northbound I-75 will be reduced to a single lane after the Stickney-Lagrange exit for work needed to set up the detour.

That work is scheduled to start after 9 a.m. Tuesday and be done before the morning rush hour on Wednesday.

In hope of reducing traffic volume on the detour, ODOT will post a sign on northbound I-75 in Wood County urging through traffic to exit at State Rt. 795 in Rossford and take that east to northbound I-280.

Motorists using that alternative route will rejoin the detour followers on I-280 at Central, but they’ll avoid any backups associated with the Central ramps’ sharp curves. They’ll also skip around congestion that routinely occurs leading into an I-75 reconstruction zone between Dorr Street and the I-475 “Jeep Split” in central Toledo.

ODOT message-board signs on northbound I-75 at Dowling Road in Middleton Township already routinely list estimated travel times to reach Michigan via the 795-to-280 route as well as direct on I-75, and those estimates will continue, ODOT officials said Friday.

For motorists starting northward trips closer to Toledo, other alternatives exist. The most obvious is to take Erie and Cherry streets and Greenbelt Parkway to short-cut through downtown Toledo to northbound I-280 — although if too many drivers do that, backups will result.

Once its exit from northbound I-75 reopens, Detroit Avenue will be another option, using Alexis Road eastbound to get back to the freeway.

And anyone headed to northbound I-75 from West Toledo should certainly consider using city streets to reach eastbound Alexis.

Those going to Detroit Metropolitan-Wayne County Airport, however, may want to avoid both the I-75 work in Toledo and a Michigan Department of Transportation project in Monroe by taking U.S. 23 north from metro Toledo and then going east on I-94.

Finally, Manhattan Boulevard is likely to attract overflow traffic whenever northbound I-75 backs up approaching the detour route, especially after the Phillips Avenue exit reopens this summer. Manhattan’s ramp to northbound I-280 leads directly to northbound I-75 just north of the closed bridges.

But Manhattan is posted with a 6,000-pound weight limit, so any heavy-truck drivers who choose it as a way around I-75 do so at the risk of being pulled over by police.

Capt. Ron Frederick, a Toledo police spokesman, said Friday that trucks diverting onto Manhattan during I-75 congestion was a main reason the police department reinstated its truck weight enforcement unit this year.

The department has no immediate plans to step enforcement up beyond extra patrols already assigned to that area, Captain Frederick said, but that could change.

Predicting how motorists will react to the I-75 detour, he said, is like “putting water in a bag” and squeezing it.

“We’re going to have to see what people decide is the best way to go,” the captain said.

Similarly, he said, many motorists already end up on Erie Street when northbound I-75 is backed up by the on-going reconstruction north of Dorr, so another obstacle farther north may not change things much.

The I-75 reconstruction between Dorr and the “Jeep Split” is scheduled to wrap up in late summer, but from the “Jeep Split” north to Phillips Avenue, ongoing freeway work will continue into 2018.

Work at the I-280 junction is part of a $62.6 million state contract for rebuilding I-75 between that junction and Phillips Avenue. ODOT officials said closing the bridges was the only way for contractor Kokosing Construction Co. to keep it on schedule for completion next year once the soil problem was discovered.

To maintain traffic on part of the bridges during reconstruction, ODOT said, would require redesigning retaining walls that were determined to be inadequate for the soil conditions, and that redesign would delay the project.

Work required to set up the detour — most notably, the temporary ramps at Central — is adding more than $1 million to the project’s cost.

Using I-280 as the I-75 detour route will require temporary lane changes on I-280 to handle the extra volume.

In particular, northbound I-280 will merge temporarily from three lanes to two beginning at the Greenbelt Parkway interchange so traffic coming in from the temporary loop at Central will have dedicated lanes. Stripe painting for this change will close the Greenbelt entrance to northbound I-280 from 9 a.m. until 3 p.m. today, after which the Manhattan exit from northbound I-280 will close from 3 p.m. until 7 p.m.

Contact David Patch at: dpatch@theblade.com or 419-724-6094.

First Published May 23, 2016, 4:00 a.m.