公路交通是现代工业国家的生命线，为了缓解日益沉重的公路交通负担，一些发达国家纷纷投人巨资在智能化交通体系的研究上，并取得了很大突破。交通拥挤和公路阻塞已经成为许多国家的一个重要难题。例如在美国，大城市周围高速公路的超负荷运行已使最高峰时的汽车时速降至不到5 Road traffic is the lifeline of modern industrial countries. In order to alleviate the heavy burden of road traffic, some developed countries have invested heavily in the research of intelligent traffic system and have made great breakthroughs. Congestion and road congestion have become an important dilemma in many countries. In the United States, for example, the overloaded operation of highways around metropolitan cities has reduced the car's speed at the peak to less than 5