A lane of an intelligent highway could probably handle the maximum number of cars (6,000) ff there were only a few ______.
查看答案
______ will be the two obstacles to the development of smart cars and intelligent highways according to the author.
Around the world there may be as many as a million and a half traffic fatalities every year.
Driving while talking on a cell phone is almost as dangerous as driving after drinking.
At the beginning the passengers in the self-driven cars tested in San Diego felt ______.