PHOENIX– Cox Communications officials say they can save three percent in gas mileage by properly inflating tires on an automobile, which may also translate into an extra mile per gallon for trucks. As such, Cox is paying $2,000 to set up a nitrogen-filling system for its 1,400 vehicles, according to Officials said it is safe because nitrogen is an inert gas and won't burn.

The project is part of a broad effort at Cox to cut energy costs, from adding solar electricity to its communications system and headquarters to reducing the fuel used in its fleet vehicles.

Consumer Reports published a study in October on filling passenger-vehicle tires with nitrogen instead of air and found that nitrogen-filled tires retained their pressure slightly better.

Cox might also contract with a company that washes fleet vehicles with recycled water instead of one that doesn't. Even if the cost is slightly higher, companies with more sustainable business practices are a safer bet for the company to partner with, Cox said.