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The new 30-mile expressway under construction in Cobb County will cost $800 million.

And commuters will be chipping in.

People who drive on the Northwest Corridor can expect to pay a flat fee of 50 cents to use the Northwest Corridor.

That’s the 30-mile reversible toll expressway on I-75 and I-575.

State officials say the cost could rise to 35 cents per mile during heavy traffic times.

“You know, whatever it needs to be to keep it moving at 45 mph so they will adjust toll based on that need and demand from consumers who use the system,” said Jill Goldberg, a spokeswoman for the Georgia Department of Transportation.

The toll figures aren’t final yet.

“Once a range has been established by our board, the actual toll amounts will be calculated using dynamic pricing based on a number of factors that include distance, speeds and number of vehicles in the lanes,” said Matt Markham, with the State Road and Tollway Authority.

The Northwest Corridor is scheduled to open in mid-2018.