袁雯倩

城市中的交通堵塞狀況愈加嚴重，在有些人看來，似乎城區(qū)面積越擴展越不夠用， 越修路，路卻越堵，究竟是什么原因呢？Prof Yuki Sugiyama認為原因主要是汽車太多。

Many traffic jams leave drivers puzzled as they finally reach the end of a tail-back to find no visible cause. An accident？ Construction work？ No， just too much traffic—too many cars， says a Japanese team led by Prof Yuki Sugiyama of Nagoya University， who has spent more than a decade puzzling over the problem.

The real origin of thesnarl upoften has nothing to do with obvious obstructions such as accidents or construction work but is simply the result of there being too many cars.

The team discovered the importance of traffic density by applying techniques to model the movements of lots of particles to real-life moving traffic. The research shows that even tiny fluctuations in car-road density cause a chain reaction which can lead to a jam.

The team also studied cars driving around a round track with an edge of 230m. They put 22 cars on the road and asked the drivers to go steadily at 30km/h （19mph） around the track. While the flow was firstly free， the effect of a driver changing his speed reverberated around the track and led to brief standstills.

Prof Sugiyama says， “Although the jam in our experiment is small， its behavior is not different from large ones on highways. When a large number of cars， beyond the road ability， are injected into the road one after another， the density seriously exceeds the value and the free flow state becomes unstable.”

The research suggests that it might be possible to guess the serious density of roads， making it possible to build a road fit for the number of drivers that need to use it.

According to the passage， answer the following questions.

1. From the first paragraph， we know that? ? ? ? ? ??.

A. many traffic jams leave drivers puzzled because of the accidents

B. there are many traffic jams mainly because of too many cars

C. Prof Yuki Sugiyama has spent ten years puzzling over the problem

D. Prof Yuki Sugiyama is a professor who is in charge of traffic jams

2. The underlined part “snarl up” probably refers to? ? ? ? ? ??.

A. origin B. construction work C. traffic jam D. accident

3. According to the passage， in order to reduce traffic jams，? ? ? ? ? ??.

A. driver should drive slowly and pay attention to the front cars

B. driver should change his speed reverberated around the track

C. people should pay more attention to the traffic speed

D. people should pay more attention to the traffic density

4. In Prof Yuki Sugiyamas opinion，? ? ? ? ? ??.

A. his experiment's behavior is not different from large ones on highways

B. the jams in his experiment are not different from large ones on highways

C. his experiment's behavior is quite different from large ones on highways

D. the large number of cars which are beyond the road ability become unstable