大学英语综合教程 第四册 Unit 2A

[03:50.60]any moment and warn of traffic jams.We already have twenty-four Navstar satellites orbiting the earth,
[04:00.08]making up what is called the Global Positioning System.
[04:04.63]They make it possible to determine your location on the earth to within about a hundred feet.At any given time,
[04:13.75]there are severalGPS satellites orbiting overhead at a distance of about11,000miles.Each satellite contains four atomic clocks
[04:25.37]which vibrate at a precise frequency,according to the laws of the quantum theory.
[04:31.85]As a satellite passes overhead,it sends out a radio signal that can be detected by a receiver in car's computer.
[04:41.04]The car's computer can then calculate how far the satellite is by measuring how long it took for the signal to arrive.
[04:49.61]Since the speed of light is well known,any delay in receiving the satellite's signal can be converted into a distance.
[04:58.15]In Japan there are already over a million cars with some type of navigational capability.
[05:05.57](some of them locate a car's position by correlating the rotations in the steering wheel to its position on a map.)
[05:13.51]With the price of microchips dropping so drastically,future applications of GPS are virtually limitless.
[05:21.98]"The commercial industry is poised to explode,"says Randy Hoffman of Magellan Systems Corp.,
[05:30.36]which manufactures navigational systems.Blind individuals could use GPS sensors in walking sticks,
[05:39.14]airplanes could land by remote control,
[05:43.29]hikers will be able to locate their position in the woods-the list of potential uses is endless.
[05:50.66]GPS is actually but part of a larger movement,called "telematics,"
[05:55.96]which will eventually attempt to put smart cars on smart highways.Proto-types of such highways already exist in Europe,
[06:05.94]and experiments are being made in California to mount computer chips,sensors,
[06:12.63]and radio transmitters on highways to alert cars to traffic jams and obstructions.
[06:19.84]On an eight-mile stretch of Interstate 15 ten miles north of San Diego,
[06:25.90]traffic engineers are installing an MIT-designed system which will introduce the "automated driver."
[06:34.21]The plan calls for computers,aided by thousands of three-inch magnetic spikes buried in the highway,
[06:41.62]to take complete control of the driving of cars on heavily trafficked roads.
[06:48.65]Cars will be bunched into groups often to twelve vehicles,only six feet apart,traveling in unison,and controlled by computer.
[06:58.13]Promoters of this computerized highway have great hopes for its future.By 2010,
[07:06.96]telematics may well be incorporated into one of the major highways in the United States.If successful,by2020,
[07:16.79]as the price of microchips drops to below a penny a piece,
[07:22.01]telematics could be adopted in thousands of miles of highways in the United States.
[07:27.70]This could prove to be an environmental boon as well,saving fuel,reducing traffic jams,decreasing air pollution,
[07:36.95]and serving as an alternative to highway expansion.