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1“Phantom” Traffic Jams Are Real- And Scientists Know How to Stop Them A) Traffic jams are a common problem of most big
2cities, either in developed or in developing countries, but one kind of traffic jams in particular can be especially
3frustrating. These are generally known as “phantom” traffic jams, in which dense traffic crawls to a halt for no
4apparent reason at all. B) “When caught in such a traffic jam, it is common for drivers to assume that there must be an
5accident, or construction or something,said Massachusetts Institute of Technology (MIT) computer science professor
6Berthold Hom. "And then you drive and drive and drive... and there isn't anything there." C) The exact cause of these
7phantom traffic jams has long remained a mystery. But now, new research has found the cause and researchers may have
8come up with a solution fbr this frustrating traffic pattern: maintaining equal spacing between cars on the road, rather
9than driving so closely behind another vehicle that a collision (碰撞)is likely if that vehicle brakes suddenly. D) Hom
10said phantom traffic jams are an emergent property of the flow of vehicles down a highway. A phantom jam begins when a
11car in dense traffic slows down even slightly, which causes the car behind that vehicle to slow even more- and the
12slowing action spreads backward through the lane of traffic like a wave, getting worse the farther it spreads.
13Eventually, the cars far behind are forced to stop completely or risk hitting the slower vehicles ahead- and so the
14traffic grinds to a halt over nothing, Hom said. E) Hom has been working on the problem of phantom traffic jams fbr
15years, and he has come up with a solution: By splitting the difference between the cars in front and the cars behind,
16the spacing of cars in a stream of traffic can act as a damper (抑制)on phantom traffic jams. That is, it can prevent the
17slow-down effect from being amplified (增强)by the cars that follow behind, he said. In essence, each driver would
18constantly make adjustments to keep their car roughly halfway between the car in front and the car behind. F) Hom calls
19this method of vehicle spacing bilateral (双边的)control, and he said it could be achieved with relatively simple
20modifications to the adaptive cruise control that many new cars already have. Adaptive cruise control is a driver
21assistance technology that sets a maximum speed fbr vehicles and automatically slows the speed of the car when traffic
22is sensed in front of the vehicle. The technology is also known as autonomous cruise control. Such modifications, Hom
23said, could help fight phantom jams within a few ears, maybe decades before an alternative solution, such as networked
24self^driving cars, becomes a reality on the roads. G) Traffic jams are caused by a number of factors, such as roads that
25are poorly designed or over-capacity, localized factors like city traffic-lighting patterns, and events like accidents
26and construction. But phantom traffic jams can make all those problems worse, Horn said. And the researchers in the new
27study have calculated that solving phantom jams could save at least some of the estimated $121 billion per year that
28traffic jams are estimated to cost the U.S. economy, Hom told Live Science. H) New research by Horn and MIT postdoctoral
29associate Liang Wang, published in the journal IEEE Transactions on Intelligent Transportation Systems, shows how
30bilateral control can fight the problem. The researchers made computer models of real-world traffic conditions, showing
31how a typical U.S. freeway could benefit from cars using bilateral control. That would be in place when human drivers
32fail to slow down, thus avoiding tailgating (紧足艮)the car in front, Hom said. 4tUnder reasonable conditions today, you
33might get 1,800 cars per lane per hour throughput (the volume of traffic passing through),he added. "But with bilateral
34control, you could almost double that." I) The main alternative to increasing traffic throughput per lane has been to
35build more lanes and more highways, and putting in new roads is very expensive, he said. "If we can increase the
36throughput on major highways, even if ifs only by 50 percent, that would be a big deal,“ Hom said. J) With the help of
37engineering students at high schools in Maine, Hom and Wang have also built a robot simulation (模寸以)that shows how
38bilateral control can suppress phantom traffic jams. Increasing the pacing of vehicles dampens the effect of slowdowns
39by cars in front of a given car, so that the slowing is not worsened until it becomes a phantom jam, the researchers
40said. K) A video from the project shows a train of autonomous robots running along a track without bilateral control;
41they eventually back up in phantom jams. But when the robots are switched over to bilateral control (by flashing the
42lights in the room), each autonomous robot tries to keep itself halfway between the robot in front and the one behind;
43the phantom jams disappear as a result, Hom said. L) Since starting his research on phantom traffic jams, Hom has
44learned that schools of fish and flocks of birds and bats use similar spacing strategies to avoid hitting each other
45while swimming or flying in densely packed groups. In particular, studies of millions of bats emerging at dusk from
46caves in Southeast Asia showed that each bat used a form of bilateral control to reduce the likelihood of collisions
47with other bats in the densely packed swarm (一大群)，Hom said. M) Unlike bats, birds and fish, however, humans have
48difficulty judging distances behind them. To address that weakness, Hom is now working with the car company Toyota to
49enable a form of bilateral control via modifications to existing adaptive cruise control systems, which use
50forward-facing sensors to judge the distance to the vehicle ahead. The bilateral control approach would include adding
51rear-facing sensors to determine the distance to the vehicle following a car. N) But until those systems become
52standard, human drivers can help reduce phantom traffic jams simply by not following the car in front so closely. As Hom
53argues, “There's absolutely no advantage of tailgating the car in front of you.”
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