Construction starting this week on widening the 5 Freeway south of El Toro Road

Overnight lane closures begin this week on the 5 Freeway from Oso to Alicia parkways in Mission Viejo, as construction starts to widen the road in south Orange County.

The Orange County Transportation Authority’s $581 million project – expected to take until 2025 – will add a second carpool lane in each direction from El Toro Road to Alicia Parkway, and a general purpose lane in each direction between Alicia and Avery parkways.

Also, merging lanes and new sound walls will be added. Two interchanges will be reconstructed. For example, La Paz Road, which runs below the freeway, will be reconstructed to add a bike lane in each direction for pedestrian and cyclist safety.

This week from Oso to Alicia parkways, the lanes closest to the center median will be closed from 10 p.m. to 5 a.m. Other lane closures will occur throughout the construction, mostly during overnights Sundays through Thursdays, OCTA spokesman Eric Carpenter said.

During the day, most of the construction work will be done behind concrete barriers, which could reduce or eliminate shoulder lanes.

No full freeway closures are planned, Carpenter said. Drivers can get updates at OCTA’s project website.

There also may be some ramp closures of up to 55 hours, although no consecutive ramps will be closed at the same time.

Agency officials have said the project is necessary to address the growing congestion in the Saddleback Valley region. More than 350,000 vehicles pass through the 6.5-mile stretch each weekday, with that number projected to grow to 450,000 by the mid-2040s, Carpenter said.

The project is divided into three segments, with the Oso to Alicia parkways segment as the first under construction. OCTA is still negotiating contracts for the other segments, with construction expected to start in 2020, Carpenter said.

The project is largely funded through the half-cent sales tax voters approved in 2006 for transportation projects, Carpenter said.