关于“州际公路”的号码; how US interstate highways are numbered

大家好，如果你开车在美国，这个邮件可能帮助你，因为我想讲解，州际公路号码。

Hello, if you are driving in the U.S., this note may help you, because in it I will explain how U.S. interstate highways are numbered.

第一，州际公路总是有红，白和蓝的牌子。 Interstate highway signs are in the shape of a shield. The sign is red on top, white in the middle and blue on the bottom. Please see image.

The way interstate highways are numbered tells you their direction or function.

If the interstate highway number has one or two digits, then

- if it is even number, it runs east-west, for example Interstate highway 80 (简称 I-80) runs from New York to San Francisco, and I-10 runs from Los Angeles to Jacksonville, Florida. The interstate numbers increase from south to north.

- if it is odd number, it runs north-south, for example I-5 runs from Washington State to San Diego, and I-95 runs from Maine to Florida. The numbers increase from west to east.

If the interstate highway number has THREE digits, then you must look at the first digit.

- if the first digit is odd, then the highway goes into the middle of a city and simply ends. This type of highway is known as a "spur." For example, I-395 in Washington connects at one end to I-95 in Virginia. But the other end is New York Ave., within Washington itself. That is, it does NOT connect to another interestate highway. Likewise, I-395 in Baltimore connects at one end to I-95. But the other end goes into downtown Baltimore, near the Inner Harbor, and simply stops.

- if the first digit is even, then the highway is either a circular one (好像北京的环路）or it is a radial highway, i.e. one that connects at each end to another interstate highway. For example, I-495 in Washington (名称“Capital Beltway") simply circles that city, just like I-695 circles Baltimore or I-285 circles Atlanta. I-676, in Philadelphia, connects to I-76 on one end and to I-95 on the other.

如果我的邮件对你没有兴趣，就是，如果你觉得，这个邮件没有意思，没关系，我不跟你生气，哈哈哈哈哈哈哈。

谢谢。