Traffic problems have become one of the major problems in cities.Streets are always crowed with vehicles and pedestrains, especially in rush hours.What is more, traffic accidents have made streets become one of the most dangerous places.But why is this problem becoming more and more serious in spite of the continuous improvement of traffic facilities?

　　交通问题已经成为城市里的主要问题之一。街道上总是车辆拥挤，行人如潮，特别是在交通高峰时更是如此。而且，交通事故使街道变成了危险的地方。尽管我们不断改进交通设施，为什么交通问题变得越来越严重呢?