| 阅读理解 “There were no rush hours any more ”said Charles M．McLean who runs the nation's busiest road．“We have rush periods and they keep getting longer and longer．” McLean was describing Chicago's 235 mi1es 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 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 Road entrance 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 l8 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 Chicago system is the“coming thing”．Systems like Chicago's are already in use on some expressways in Los Angeles and Houston．“Chicago has taken the lead ”says New York City's traffic director and he adds “We are far behind…!” |