It involved the creation of a new section of road next to the current one.
The old road was formed into a slip lane, where people can pull off the main highway and park, allowing students to access the school more safely.
Mayor Grant Smith says the road will keep students and other road users safe.
"This work was vital to keep the students safe, but also because the wider Whakarongo suburb is one of the city's fastest-growing areas.
"With more housing planned for the area it is vital this area is made safer for all road users and pedestrians.
"The staff, students and parents of Whakarongo School have been incredible to work with during this project.
"They've understood what a huge impact this project will have on their safety and as a result been very patient and understanding during construction.
"We are thrilled to be able to celebrate the opening with them."
Palmerston North City Council chief executive Heather Shotter says it's been great to see one of the big projects completed after Covid-19.
"Having to halt some of our biggest construction projects has been as frustrating for us as it has been for our contractors and those most closely impacted by the work.
"It is great to see this project complete and is a sign that our city is well and truly in recovery mode."
Smith says the next step is working closely with the Transport Agency to get the speed limits changed in the area and advance further safety improvements at other junctions on SH3 Napier Rd.
"The state highway that runs through Whakarongo is just too dangerous and will continue to be a problem as the area grows.
"It is heartbreaking to hear news of constant crashes happening on this stretch of road.
"I'll be continuing to press the Transport Agency to announce additional safety and intersection improvements, including reductions in speed limits for this stretch of road, to ensure our residents and visitors are as safe as possible on our city's roads."