RICHMOND, Va. — The federal government has approved a key low-interest loan required to build new private toll lanes on Interstate 66 between Gainesville and the Beltway, Virginia Gov. Terry McAuliffe said Thursday.

The $1.2 billion loan approval will allow the private companies designing, building and operating the lanes to secure final financial backing, known as “financial close,” over the next few weeks.

Final designs for the 22 miles of new toll lanes in each direction were just released, ahead of final design public hearings next month.

Construction could begin later this year, with work ramping up along the length of the project area next spring.