"Backwards" California I-5 3di

[Quillz]

I think this was asked before, but I can't find the thread...

I noticed at some point California seems to have numbered its even numbered I-5 3di the inverse of the guidelines. Generally it's recommended to do lower numbers in the south and higher numbers in the north, but instead we got 805 as the southernmost, 405 in the middle, 205 in the north.

Is there a specific reason for this?

[NE2]

Where are those guidelines stated?

[Quillz]

Where are those guidelines stated?

I don't think they are ironclad stated anywhere, but it's more convention based on past patterns. Like how US routes would have 2di increase as you went westward and southward, and interstates would be reversed. If you look at most 3di in other states, you can see this trend (New York having 190, 390, 590 generally eastward, and so on).

[NE2]

Yeah, I don't think there are any such guidelines.

[Max Rockatansky]

Part of I-5W was renumbered as 505 in 1964.  Even still, you had the original I-105 in downtown Los Angeles.  The only kinda-sorta pattern with the even three digit spurs I-5. 

California wanted several different things with Interstate numbering conventions between 1957-1958:

https://www.gribblenation.org/2022/11/establishing-numbering-conventions-of.html?m=1

[vdeane]

Where are those guidelines stated?

I don't think they are ironclad stated anywhere, but it's more convention based on past patterns. Like how US routes would have 2di increase as you went westward and southward, and interstates would be reversed. If you look at most 3di in other states, you can see this trend (New York having 190, 390, 590 generally eastward, and so on).

While many states tried to do some kind of geographic system, many didn't.  Starting with low numbers and moving to high numbers as more 3dis are designated (chronological order) is also common.

[kphoger]

So, basically, it's not a guideline, and nobody recommended it.