Interstate 10S and the original Interstate 110 in California

[cahwyguy]

Tom didn't do an AARoads post when he posted https://www.gribblenation.org/2024/03/interstate-10s-and-original-interstate.html . I was going through the post as I was working on highway page updates. Most of the post isn't directly related to Route 10S, and focuses more on general US 60 / US 70 / I-10 history, with a bit of the short-lived I-110 thrown in.

However, it is incorrect with respect to Route 10S, because it is a bit more confusing.

Look closely at the Postmile tool. In the short stretch between US 101 and I-5, there are TWO different designations.

Route 10, with "S" postmiles, is the mainline. I think these are "S" postmiles in the spur sense, not realignment of "R" miles, and I think Tom is correct in noting they are not counted as part of I-10's chargable miles. He is also correct in that the route is so short there is no reassurance signage of I-10, so they can be ambiguous.

Route 10S is something different, and if you look closely in the Postmile Tool, you'll see 10S extends onto US 101 ending at Alameda Avenue. Route 10S is the designation for the El Monte Busway.

So, in this stretch, you have both Route 10 "S" postmiles, AND Route 10S with regular postmiles.

To see, look up Route 10S, LA 17.024 in the PM tool, or Route 10 LA S0.266, or Route 10S LA 18.012.

Daniel

[ClassicHasClass]

After CA 86S became mainline 86S, I think 10S is the last of those suffixed routes, yes? (Still hoping an 86S shield turns up in a scrapper yard.)

[Max Rockatansky]

There are a couple others that I've hit on over the last year like 40S in Barstow and 5S in Glendale.  I got something for 178S in Bakersfield coming up also this month (not sure how I forgot to post this one).  That also doesn't account for the very much signed 14U.

[cahwyguy]

There are a couple others that I've hit on over the last year like 40S in Barstow and 5S in Glendale.  I got something for 178S in Bakersfield coming up also this month (not sure how I forgot to post this one).  That also doesn't account for the very much signed 14U.

Remember: There is a distinction between suffixed (10S) routes, and routes with S postmiles. The only SUFFIXED routes are: two instances of 5S, 10S, 15S, 880S, and 178S
https://gisdata-caltrans.opendata.arcgis.com/datasets/77f2d7ba94e040a78bfbe36feb6279da_0/explore?filters=eyJSdGVTdWZmaXgiOlsiUyJdfQ%3D%3D

Notably, Route 40 in Barstow is NOT Route 40S.

The "S" postmile prefix is found on Routes 4, 7, 10, 18, 38, 40, 101, 178. Note that the "S" PM Prefix is either Spur or realignment from "R". See https://gisdata-caltrans.opendata.arcgis.com/datasets/77f2d7ba94e040a78bfbe36feb6279da_0/explore?filters=eyJQTVByZWZpeCI6WyJTIl19

Route 10 is notable for having both Route 10 PM Prefix S and Route 10S on distinct roadways next to each other. The Route 178S PMs also seem to be S Prefix. Tom's blog post erred in that it talked about 10S, when it means Route 10 "S" PM Prefix. Route 10S is the El Monte busway, and runs from Union Station much further (to near the 710 or the 605, if memory serves correct).