A two-year project to construct the $14 million State Highway 1 Edendale realignment has reached the halfway mark.

Due for completion in mid-2020, the realignment will improve safety and increase accessibility for Southland communities and businesses.

According to an New Zealand Transport Agency (NZTA) update newsletter, work is underway on building the fourth leg of the roundabout that will serve as the new milk tanker access road for the Fonterra dairy plant.

Site clearance work including tree felling has commenced in advance of water and power relocation/ installation and pavement construction.

"Recent wet weather has slowed progress on this work a little," the update says.

Work in progress includes the pavement construction of the Fonterra access road, the tie-ins at each end to SH1 and into the Edendale township.

"We also need to do more sealing, applying line markings, installing safety barriers and landscaping."