Mr McCarthy said an interesting method of construction was being employed - building from the top down.
First trench walls were built, then bridges connected to the walls. The earth below the bridge was then dug out. The floor was constructed and tied to the trench walls.
"The first bridge is already done and the second should be done by May next year," Mr McCarthy said.
The project had not been without challenges. The huge amount of dirt that needed to be brought in, meant a lot of trucks were travelling through the area causing traffic congestion, however, that phase was completed.
The workers also found asbestos near the Old Scout Hall, which was a surprise.
The open day informed people about the environmental effects of the huge roading project and showed videos and models of what the finished underpass would look like.