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  3. Sitting in stationary traffic is, at best, a Zen experience. Drivers mired in a jam learn to cede control to the powers that be,

Sitting in stationary traffic is, at best, a Zen experience. Drivers mired in a jam learn to cede control to the powers that be,

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问题     Sitting in stationary traffic is, at best, a Zen experience. Drivers mired in a jam learn to cede control to the powers that be, becoming at one with the universe as they breathe in the mind-numbing fumes all around. At worst, it is an on-going battle for sanity. But now, according to several groups of researchers in America and Germany, there is something that drivers can do to take back control over the roads. Get adaptive cruise control. And, of course, use it.
    Adaptive cruise control (ACC) , as its name suggests, is a modified version of traditional cruise control. It employs radar to monitor the road ahead of a vehicle, automatically adjusting that vehicle’ s speed to maintain a safe distance from the one in front. This is safer than manual driving because it reduces the system’ s reaction time from nearly a second (human) to practically instantaneous (machine) , thus helping to forestall shunts. But ACC may have a useful side-effect, arising from the fact that another effect of slow human reaction times is to produce traffic jams on apparently open roads.
    Such jams start when a car slows suddenly to allow, for example, another vehicle to enter the traffic stream. Slow reaction times mean that instead of responding smoothly, the drivers behind such a vehicle often end up slamming on the brakes. That skimming propagates backwards, and before long (he traffic is at a standstill. So it makes sense that ACC would reduce not only collisions, but also congestion. What is unexpected is how few vehicles need to have it operating for all to benefit. As Craig Davis of the University of Michigan reports in Physical Review E, only 20% of cars need to employ ACC in order to present completely those jams that are caused by a slow lead car on a high-speed, single-lane road. According to Dr. Davis’ s computer model, even a rate of use of ACC as low as 13% can improve the flow of traffic significantly.
    ACC is not a panacea. Dr. Davis got less promising results for more complex, road conditions, particularly those near junctions. And a .similar model built by Boris Kernel’, a researcher for Daimler Chrysler, in Stuttgart, Germany, indicates that in certain bottleneck conditions, ACC may even cause extra congestion. These disappointing results can, however, be ameliorated by shortening the "headway" in ACC-equipped vehicles, according to Martin. Treiber of the Dresden University of Technology’, also in Germany.
    Headway is the gap, measured in seconds, that a driver puts between himself and the car ahead. Since ACC reacts more quickly than a human, people who have it fitted can afford to allow less headway.
    Summary :
    Stationary traffic can drive people mad. However, according to American and German researchers, adaptive cruise control (ACC) can help drivers take【71】. ACC adapts a car’s speed to keep a sale distance from the one ahead by using radar to monitor the road ahead. ACC is safer than manual driving because is significantly reduces the system’s【72】, and collisions and congestion in addition. According to Dr. Davis’ computer model, if【73】of cars use ACC, the flow of traffic can be improved significantly. However, ACC should not be seen as a panacea. In【74】conditions, it may even cause extra jams, according to a computer model. But this situation can be improved by reducing【75】in ACC-equipped vehicles.
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答案complex road／bottleneck
解析 (第四段开头，Dr．Davis got less promising results for more complex road conditions，即更复杂的路况下，Dr. Davis的实验结果就不那么鼓舞人心了。答案也可从下句得出，即And a similar model．．．indicates that in certain bottleneck conditions．ACC may even cause extra congestion。)
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