Up to 20,000 vehicles a day will use the new N25 New Ross bypass, which is officially being opened today.
The road will allow motorists travelling between Waterford and Wexford to avoid New Ross, a familiar bottleneck over the years.
The route is 15km in length and cost €230m to build. It includes Ireland's longest bridge.
The Taoiseach will officially open the project this afternoon and it will be open to public traffic from midday tomorrow.
Seán Dobbs from Wexford County Council says it will benefit the entire southeast region.
"It will cater for traffic, up to 15,000-20,000 per day," he said.
"It's going to take a significant amount of commuter traffic out of New Ross town itself and, very significantly, a huge amount of freight and heavy good traffic from the streets of New Ross."