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Why do the Boston and Washington Beltways have the same number (495)? https://en.wikipedia.org/wiki/Interstate_495_(Massachusetts) https://en.wikipedia.org/wik

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

martingordon 10y ago
> 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_Highways https://en.wikipedia.org/wiki/List_of_auxiliary_Interstate_H...
Sanddancer 10y ago
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.
jwn 10y ago
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.
- dajohnson89 10y ago
  You mean both loops spur off 95 :-) but yeah that makes sense
douche 10y ago
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.
- 24gttghh 10y ago
  But I-495 is not signed as such; it is simply called the 'Falmouth Spur' ;)
jcranmer 10y ago
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.

martingordon 10y ago

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

Sanddancer 10y ago

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.

jwn 10y ago

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.

dajohnson89 10y ago
You mean both loops spur off 95 :-) but yeah that makes sense

douche 10y ago

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.

24gttghh 10y ago
But I-495 is not signed as such; it is simply called the 'Falmouth Spur' ;)

jcranmer 10y ago

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.