"We don't have rush hours any more", said Mr. Charles Mac Lean, who runs the nation's busiest road. "We have rush periods, and they keep getting longer and longer." Mac Lean was describing prefix = st1 /Chicago's 235 miles of expressway. But the same might be said about almost any of the expressways that have become an important part of American city life--and about the heavy traffic that often blocks them. In Chicago, a computerized system has been developed that controls traffic on the city's seven expressways. Now one man--a controller--can follow the movement of Chicago's traffic by looking at a set of lights. The system uses electronic sensors that are built into each expressway, half a mile apart. Several times a second, the computer receives information from each sensor and translates it into green, yellow, or red lights on a map in the control room. A green light means the traffic is moving forty-five miles an hour, yellow means thirty to forty-five miles an hour and red means heavy  traffic--cars standing still or moving less than thirty miles an hour. "See that red light near Austin Avenue?" the controller asked a visitor. "That's a repair truck fixing the road, and the traffic has to go around it". At the Roosevelt Roadentrance to the expressway, the light kept changing from green to red and back to green again. "A lot of trucks get on the expressway there," the controller explained. "They can't speed up as fast as cars." The sensors show immediately where an accident or a stopped car is blocking traffic, and a truck is sent by radio to clear the road. The system has lowered the number of accidents by 18 percent. There are now 1.4 deaths on Chicago's expressways for each one hundred million miles traveled, while in other parts of the country there are 2.6. Traffic experts say that the Chicagosystem is the "coming thing". Systems like Chicago's are already in use on some expressways in Los Angeles andHouston. "Chicago has taken the lead," saysNew York City's traffic director; and he adds, "We are far behind..." Which of the statements is true about the computerized system in Chicago?
It changes rush hours into rush periods. It saves a lot of labor and meanwhile prevents some deaths. It is the first system of this kind in America. It will soon be followed by New York City.