Construction on I-75 in Oakland County is set to ramp up again next month with an 8.5-mile overhaul as well as the state's first carpool lane and two more interchange projects.

Segment two of the nearly $2 billion I-75 Modernization Project will include redoing the freeway from Coolidge Highway to 13 Mile Road. The Michigan Department of Transportation is aiming to start mid-March, but work will be dependent on the weather.

That means traffic on that stretch will be reduced to two lanes each way. The downside is traffic delays; the upside is new roads and safer, innovative designs, such as the state's first carpool lane, Rob Morosi, spokesman for the MDOT, said Monday morning during a media update.

"We will keep traffic moving on I-75 during this monumental project," Morosi said. "It's going to be incredibly busy on I-75."

Beginning next month, all northbound traffic on I-75 from 13 Mile to Coolidge will be shifted to the southbound side, where there will be two lanes open in each direction. Crews will overhaul the northbound side with an expected completion in November, when all traffic on I-75 will return to normal for the winter.

In 2020, the situation will be reversed, with all southbound traffic shifting to the newly rebuilt northbound side. In late fall of 2020, the project should be complete, with all traffic returned to normal.

From March to November, all exits on I-75 will remain open unless MDOT crews are working to rebuild them. Entrance ramps at 12 Mile and Corporate Drive will remain open.

MDOT selected Walsh Construction Co., which has a regional office in Detroit, and Wixom-based Toebe Construction LLC for the $224 million second phase of the project. Segment two prep work began this fall. Segment one was completed in 2016-17 for around $90 million.

Segment two includes repairing and rebuilding 18 structures, including bridges and pedestrian walkways.

In addition, "diverging diamond interchanges" will be constructed at 14 Mile Road and at Big Beaver Road — two of the corridor's busiest interchanges. The DDIs will be the second of their kind in metro Detroit and are intended to increase safety and efficiency. The first DDI in the region was installed in 2015 at I-75 and University Drive and has so far accomplished those goals, according to MDOT.

The main function of the DDI model is to eliminate left turns in front of oncoming traffic to enter the freeway, which is accomplished by building bridges that go over 14 Mile and Big Beaver and connect directly to the freeway.

The DDI is a major component of the rebuilt I-75, which is in great need of safety enhancements, Morosi said. The 18-mile stretch of freeway that is being rebuilt in the Modernization Project was constructed in the 1960s has never been rebuilt, only patched and repaved.

The stretch averages 174,000 vehicles per day and supports 20,000 businesses. It averages 1,000 crashes per year, most of which happen on dry pavement, according to MDOT. One in five result in injury.

"This is indicative of a capacity issue," Morosi said.

The state's first HOV (high occupancy vehicle) lane will be built from 12 Mile Road to South Boulevard. Morosi said the carpool lane will be complete by late 2020 or early 2021. It will only be used as a carpool lane during peak traffic hours, to start.