Saint John police say $60,000 worth of equipment used for the One Mile House interchange project was damaged in a fire on Wednesday night.
The fire happened just before 10:30 p.m. on the side of the highway near the Crown Street exit.
A 7.6-metre trailer, which stored generators and other construction materials, was completely destroyed in the fire.
Investigators believe the fire was deliberately set.
Witnesses reported seeing a group of people wearing black clothing running from the scene.
Police tried to locate them, but lost their trail in the Rockwood Court neighbourhood.