The Roads Minister Conor Murphy has officially opened the £45 million A2 Maydown to City of Derry Airport dual carriageway.
The scheme involved upgrading 6.6km of the A2.
The minister said the project was "an important step forward for the northwest".
"It will help ease congestion, resulting in improved safety and journey times," he said.
The A2 is part of the main road connecting Limavady to Londonderry.
It also provides links to the Maydown and Campsie industrial zones and to the City of Derry Airport.
Neolithic sites unearthed
During the works a number of significant archaeological discoveries were made.
Eight Neolithic sites where unearthed, some more than 5,000 years old.
They included a pair of well-preserved 5,000 year-old Neolithic houses and 4,000 year-old Bronze Age burial places known as 'ring-ditches'.
Bronze Age pottery, flint tools and human bones were also discovered.