Tuesday night marked the night of the “big flip,” when all southbound traffic on Interstate 75 through downtown Dayton switched to the northbound lanes to accommodate construction.

Two southbound lanes were switched by about 10 p.m. Tuesday evening and the rest will are being switched overnight, Mandi Abner, spokeswoman for the Ohio Department of Transportation-District 7 said Tuesday night.

All of the switching should be completed by 6 a.m. Wednesday, she said.

It will allow three lanes southbound and two lanes northbound.

“We understand this can be frustrating and it can be an inconvenience, but we encourage motorists to slow down, be patient and use caution,” Abner said.

The closures are permanent and a new ramp is scheduled to reopen in 2016. The ramps that will close are:

* From I-75 south to First Street and Third Street

*From Monument Avenue and Second Street to I-75 south

Once southbound traffic is moved to the northbound side of I-75, crews will demolish and then reconstruct southbound I-75. The lane switchover will take place between Main Street and U.S. 35.

ODOT is advising drivers to use extreme caution in this area.

The northbound exit and entrance ramps to I-75, which closed this fall, will remain closed throughout the project.

According to ODOT, the following ramps will remain open throughout construction and serve as primary detours to access downtown:

* Jefferson Street off U.S. 35

* Main Street off I-75

* Edwin C. Moses Boulevard off I-75

The project will create three continuous lanes in both directions from Third to Main streets and upgrade pavement conditions. The $126 million project is expected to be completed in fall 2017.

In other highway alerts, ODOT said that the ramp from I-75 southbound to Webster Street will be closed nightly beginning Wednesday at 8. The closures will take place daily between 8 p.m. and 6 a.m. The ramp is scheduled to reopen to motorists Friday, Dec. 14, at 6 a.m.

This ramp closure is due to a contractor removing the existing bridge over the ramp.

The official detour during this ramp closure is SR 4 to SR 202 to Valley Street to Keowee Street to Monument Street to Webster Street.