Numbering of 3di interstates ... why not use the lowest digit available?

[TheStranger]

Though growing up in California we were lucky when any 3di number was available for a spur or loop off its 2di, let alone having them be in a pattern of any sort.

What I wonder: Is a geographic pattern why I-405 and I-605 were used before I-205, and why I-905 was chosen for the Otay Mesa spur instead of I-705?

[agentsteel53]

What I wonder: Is a geographic pattern why I-405 and I-605 were used before I-205, and why I-905 was chosen for the Otay Mesa spur instead of I-705?

the location of I-805 seems to confirm it, though I am not sure chronologically when 805 was designated, relative to 405 and 605.

however, why was 105 used as that brief segment of East LA Interchange in the beginning of the system, as opposed to 705?

[TheStranger]

What I wonder: Is a geographic pattern why I-405 and I-605 were used before I-205, and why I-905 was chosen for the Otay Mesa spur instead of I-705?

the location of I-805 seems to confirm it, though I am not sure chronologically when 805 was designated, relative to 405 and 605.

Looking at the Yellow Book scan from Froggie's page, 405, 605 both were planned in the earliest stages:

http://www.ajfroggie.com/roads/yellowbook/losangeles.jpg

Wikipedia notes in the I-805 article that that route was approved as an Interstate in 1958, so after 405/605 had first been proposed.

however, why was 105 used as that brief segment of East LA Interchange in the beginning of the system, as opposed to 705?

Looking at that above Yellow Book map, the 105/110 pair of 1964-1968 was part of the original planning, too - which is interesting given that that segment of the Santa Ana Freeway that was unsigned 105 has NEVER been upgraded to Interstate standards from what I recall.

That might explain why that was "105" as the original proposed first odd branch route from I-5.  The only other odd 3di that I-5 had (until the FHWA creation of unsigned I-305 in 1982) was I-505 from 1964 onwards, whose number (as was 580's) was derived from the former designation of I-5W.

[machias]

How about I-481 in New York and I-587/I-787? Maybe it's worth trying to complete this list. I-393 NH is another.

I-481 was originally I-281, but NYSDOT wanted to avoid confusion with NY Route 281, which is about 20-25 miles south of I-481.

[WNYroadgeek]

How about I-481 in New York and I-587/I-787? Maybe it's worth trying to complete this list. I-393 NH is another.

I-481 was originally I-281, but NYSDOT wanted to avoid confusion with NY Route 281, which is about 20-25 miles south of I-481.

The portion between the Thruway and its' southern terminus was, but the portion between the Thruway and NY 481's northern terminus was intended to be an extension of NY 57.

[Scott5114]

It's not silly.  Duplicating route numbers creates confusion giving directions, reporting location when calling 911, discussing highways among officials and legislators, creating reports like statistics for every route in a state, etc., etc.

When you duplicate route numbers across systems, you get silliness like this:

Only if you don't take care to keep routes far enough apart that it isn't a concern. OK doesn't have an issue with there being an I-44 and an OK 44, a US 56 and an OK 56, a US 266 and an OK 266, etc. (US 270 and OK 270 are kind of confusing but US 270 is concurrent with I-40 at the bit where the conflict arises, so it's likely nobody is really looking for it.)