SPRINGFIELD, Va. (AP) — A $940 million project to add express toll lanes to a 29-mile stretch of Interstate 95 in northern Virginia is running ahead of schedule and could open to drivers as early as December.

The Virginia Department of Transportation announced the revised timetable Thursday. Previous estimates had the lanes scheduled for completion in early 2015.

The lanes will stretch from the Edsall Road exit on I-395 to Garrisonville Road in Stafford County. Drivers can pay a variable toll that goes up as congestion increases to use the lanes, or they can use them for free in a carpool of three or more.

The project was built under a public-private partnership, and extends a concept already in place on a large stretch of the Capital Beltway in northern Virginia.

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