国道是国家级干线公路的简称。在国家公路网中,具有全国性政治、经济、国防意义的公路,被定为国家的干线公路。我国的国道分为三类:第一类是以北京为中心,通往各大中城市的公路;第二类是南北方向的公路;第三类是东西方向的公路。这三类的公路干线,采用三类阿拉伯数字加以区别:第一位数字表示国道类别,第二、 State Road is a national trunk highway for short. In the national road network, a nationwide political, economic and national defense highway is designated as a national trunk road. There are three types of national roads in our country: the first is the road that takes Beijing as the center and leads to major cities; the second is the north-south highway; and the third is the east-west highway. The three types of highways are distinguished by three types of Arabic numerals: the first digit indicates the type of national highway, and the second,