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Comment by dajohnson89 | Hacker News Reader

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dajohnson89·

Why do the Boston and Washington Beltways have the same number (495)?

https://en.wikipedia.org/wiki/Interstate_495_(Massachusetts)

https://en.wikipedia.org/wiki/Interstate_495_(Capital_Beltwa...

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> Because longer interstates may have many such supplemental routes, the numbers may repeat in each state along their route, but they will not repeat within a state.

https://en.wikipedia.org/wiki/List_of_auxiliary_Interstate_H...

Because there are so many auxiliary routes that they have to get reused. The main rule is that they can't be in the same state, although that's not necessarily enough to guarantee that the names don't get confusion. I-395 is the spur of 95 in Virginia into DC and the spur of 95 into Baltimore, while 695 is both in DC and in the Baltimore suburbs, which are about an hour apart in driving terms.

I-495 used to be the name of the Maine Turnpike, as well, before 2004. Now it that route is included in I-95, while the previous I-95 is now labeled I-295, while a yet third section of highway connecting the two above Portland is now technically 495.

But I-495 is not signed as such; it is simply called the 'Falmouth Spur' ;)

Spur and belt routes, the ones with three digits, are reused across states. They tend to be ones that branch off to serve particular cities and not cross state lines.

I assume because they are both loops that spur off of 495. It's definitely confusing, but it seems consistency in numbering won out over unique-ness.

You mean both loops spur off 95 :-) but yeah that makes sense

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