Automobile travel has also become much safer over the years. The U.S. Interstate Highway system provided vastly improved safety for long-distance drivers and passengers by eliminating grade-level intersections and traffic lights, by constructing medians to separate vehicles moving in different directions, and by using long acceleration lanes for vehicles entering and leaving the highway. Automobiles themselves have become much safer with the introduction of seat belts and air bags, improved tires, brakes, and steering, safer gas tanks, and many other safety features, both obvious and hidden within the structures and systems of cars. Table 4.2 shown the rapid decline in U.S. fatality rates per 100 million highway vehicle miles traveled in recent decades.