对于一个大城市来说,交通问题影响到城市经济的发展,也关系到居民生活,因此这个问题始终为社会各界所关注。近几年来,北京市二环、三环高速环道相继建成通车,使首都交通面貌有了很大改观。尽管如此,由于经济的迅速发展,交通量的增长速度远比道路改扩建速度高得多,因此交通仍是城市不容忽视的大问题。就北京二环、三环高速环道而言,交通高峰期不少地方已开始阻塞,车辆上不去,也下不来。随着小汽 For a big city, traffic problems affect the development of the urban economy and the lives of residents. Therefore, this issue has always been the concern of all walks of life. In recent years, Beijing’s Second and Third Ring Expressway have been opened to traffic, so that the traffic outlook of the capital has been greatly improved. Nevertheless, due to the rapid economic development, the traffic volume has been growing at a much higher rate than the road reconstruction and expansion. Therefore, transportation is still a major issue that cities can not ignore. As far as Beijing’s Second and Third Ring Expressway Ring Roads are concerned, many places at the peak of traffic have started to block. Vehicles can not go down or come down. With the steam