Four months of motorists using diversions around the Yoogali intersection on Irrigation Way ended this weekend.
The bridge over Main Drain J was opened to traffic from Friday afternoon.
Work on the intersection isn't finished, with further road widening and road surface upgrades planned for Mackay Avenue, as well as the installation of traffic lights.
Built with pre-cast concrete sections and weighing around 357,000 kilograms, a concrete slab was poured on the floor of the channel.
The bridge is the major part of the Yoogali intersection upgrade which is set to cost around $14.8 million.
The project has been paid for by the state and federal governments which have provided $10.4 million and $4.4 million respectively.
"On top of the Irrigation Way bridge now open to traffic, new wider, resurfaced lanes have also been completed on the Kurrajong Avenue and Irrigation Way intersection legs, to tie with traffic lights when the upgrade is completed," Member for Farrer Sussan Ley said.
"While work has impacted traffic for a number of months, road users can take heart in the fact the new intersection is on schedule for completion by mid-November."
NSW roads minister Paul Toole said the project employed 45 jobs and 32 contractors.