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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,

admin2013-02-03  55
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 slamming propagates backwards, and before long the 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 prevent 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 Kerner, a researcher for Daimlet 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【61】. ACC adapts a car’s speed to keep a safe distance from the one ahead by using radar to monitor the road ahead. ACC is safer than manual driving because it significantly reduces the system’s【62】, and collisions and congestion in addition. According to Dr. Davis’  computer model, if【63】of cars use ACC, the flow of traffic can be improved significantly. However, ACC should not be seen as a panacea. In【64】conditions, it may even cause extra jams, according to a computer model. But this situation can be improved by reducing【65】in ACC-equipped vehicles.
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答案reaction time
解析 (第二段，This is safer than manual driving because it reduces the system’s reaction time，即ACC之所以更安全，是因为它减少了系统反应时间。)
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