摘要
Driving in the United States and other countries, one could make an educated guess about the relative importance of a road by looking at its route marker. See Figure 8.1 for a collection of route markers from different ranks of interstates, U.S. Highways, state highways, and county roads. Roads of higher ranks tend to be wider, faster, and carry more traffic. Taking Minnesota as an example, there are approximately 19,300 kilometers (12,000 miles) of Interstates and state highways (9% of the total road length) as of 2005, which account for about 60% of the total 87 billion annual vehicle-kilometers (54 billion vehicle-miles) traveled in this state (Minnesota Department of Transportation, 2005a).
摘要译文
在美国和其他国家驾驶，可以通过观察其路线标记来猜测道路的相对重要性。美国国家公路，国家高速公路和县级公路的不同级别的路线标记汇总见图8.1。更高层次的道路往往更宽，更快，流量更大。以明尼苏达州为例，截至2005年，州际公路和国有公路（约占公路总长的9％）约为19,300公里（12,000英里），约占全年870亿公里的54％（54十亿车公里）在这个州旅行（明尼苏达州交通部，2005a）。
Feng Xie1;David M. Levinson2. Hierarchy. Evolving Transportation Networks[M].DE: Springer, 2011: 87-99