How can we make big rigs greener?

The average big rig truck gets less than seven miles per gallon of diesel fuel, making it a major expense for trucking companies. So some truck manufacturers are looking to make big rigs greener.

According to the Wall Street Journal, improving gas mileage by just one mile per gallon would be equal to removing 200,000 trucks from the road.

U.S. Xpress Enterprises chief executive Eric Fuller told the Wall Street Journal, "Fuel is such a large cost for us that we have every incentive to try to get the best miles per gallon we possibly can. Any kind of technology that helps us get there usually pays for itself."

Some truck makers like Cummins and Tesla are working on prototypes of fully electric models.

But it could be many years until electric trucks are actually on the road -- and even then, they could be very expensive.

The decision really comes down to dollars and cents, but anything companies can do to improve the environment is a big move in the right direction.