The Complete 540 project will extend the Triangle Expressway, effectively finishing the 540 loop around Raleigh.
The federal loan is worth up to $501.5 million and it will be repaid primarily through the tolls collected on the completed section of the road.
Crews began construction in early December on the first phase of Complete 540 by clearing land where the toll road will cross Benson Road at West Lake Road and I-40.
That phase of construction is expected to be open to traffic by 2023.
The whole Complete 540 project is estimated to cost $2.2 billion.