“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 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 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...!”

46. What’s the main idea of the passage?

A. A Computerized Traffic Control System greatly helps in Chicago.

B. Rush Periods in Chicago are getting longer.

C. Chicago has the busiest road in the nation.　 　　　　　　　　　　　　　　

D. The expressways are faster now.

47．What can we learn from the passage?

A. The controller follows Chicago’s traffic by waiting for the red light to turn to green.

B. The sensor can immediately deal with the accidents.

C. The system has greatly helped to reduce the deaths on the expressways.

　D. At the entrance to the expressway, the lights can change only because of the speed of the truck

48. By saying “Chicago has taken the lead,” the director means _____.

A. Chicago has taken something very heavy.

B. They are under the control of Chicago.

C. Chicago is ahead of them in using the system.

D. Chicago is the center of all the systems in the US.

49. Why did the controller ask a visitor?

A. He wants to tell him how the lights work.

B. He cited it as an example to show the visitor what the lights tell.

C. He shows the visitor what he does.

D. He was teaching him how to control the system.

50. Where is the passage most probably taken from?

A. A science book　　　　　　 B. A travel journal.

C. A magazine　　　　　　　　 D. A student text