填空题 In Chicago, a computerized system has been
developed that controls traffic in the city"s seven on
expressways now, one man—a controller—can follow
the movement of Chicago"s traffic as looking at a set of lights. 1
The system uses electronic sensors that is built into each 2
expressway, half a mile each apart. Several times 3
a second, the computer receives information for each 4
sensor and translates it into green, yellow, or red lights
in a map in the control room. 5
A green light means traffic is moving forty-five to
sixty miles an hour, yellow means heavy traffic-cars
stopping still or moving less than thirty miles an hour. 6
"See that red light near Austin Avenue?" the controller
asked a visitor, "That"s a repair truck fix the 7
road, and the traffic has to go near it." 8
At the Roosevelt road entrance to the expressway,
the light kept changing from green to red and back to
green also. "A lot of trucks get on the expressway 9
there." the controller explained, "They can"t speed
forward as fast as cars." 10
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 accidents
by 18 percent. There are now 1.4 deaths on Chicago"s
expressways for each one hundred million miles traveled,
while nationally there are 2.6.