The AARoads Wiki is live! Come check it out!

Main Menu

I-40S in Barstow

Started by Max Rockatansky, February 10, 2024, 12:03:49 PM

Previous topic - Next topic

Max Rockatansky

Interstate 40 Spur is 0.794-mile hidden State Highway which exists in the city of Barstow, California. Interstate 40 Spur originates at National Trails Highway and follows Main Street west to the vicinity of Coolwater Lane. Interstate 40 Spur is a former segment of US Route 66 which was bypassed during July 1961. The purpose of Interstate 40 Spur is to permit movement from westbound Interstate 40 to northbound Interstate 15.


^ The PQT identifies part of Main Street (from just west of I-15 to just south of I-40) as "Route 40" rather than "Route 40S". The PQT, as Caltrans does internally, doesn't differentiate between Interstate, U.S., and state routes, nor between regular, business, and other routes (except with the "S" suffix for supplemental routes), so long as they're state maintained.

Also, the Colorado Ave. Freeway Extension in Glendale, discussed in one of your recent posts, is shown in the PQT as "Route 5S" rather than part of Route 5. But FHWA's online map of the National Highway System doesn't identify the Freeway Extension nor "Route 40S" as part of the Interstate system, but rather as "principal arterial", even though the Freeway Extension is clearly freeway-grade (not necessarily Interstate-grade). I have found that tool useful in other contexts, such as to confirm "dangling" ends of Interstate routes like I-105 east of I-605, and I-780 west of I-80. Then again, it still shows I-710 ending at CA 1, despite strong signage that it extends southwest to CA 47. So I would not consider the FHWA map super-dispositive.

But I nevertheless suggest caution in describing routes like 5S in Glendale or "40S" in Barstow as "Interstate" rather than plain-vanilla state routes.
my Hot Springs and Highways pages, with links to my roads sites:

Max Rockatansky

Noted, I'll add a line to both blogs tonight noting the semantics of what Caltrans and the FHWA consider to be Route designations.  To your point, 710 north of I-10 isn't classified by the FHWA as Interstate but it is signed as such in-field.  I think that I hit on the phenomenon at hand better in the 710 blogs.


Oof.  Keep in mind as well that there are various definitions of what is considered to be an Interstate out there.

FHWA's map notwithstanding, some types of funding are based (sometimes, I suspect just by a simple reference error) upon the definition of the Interstate Highway System at one particular point of time.  Various sections of signed Interstate in NYC fall into the category of having to make sure that you're using the proper fund source on them.  They're still officially Interstates, but Congress deemed them ineligible for whatever reason.

Gets really tricky depending on the context.
Please note: All comments here represent my own personal opinion and do not reflect the official position(s) of NYSDOT.

Max Rockatansky

FWIW this example was already existing as surface highway and was more or less wedged between two chargeable corridor projects where a connection ramp movement wasn't desired.  5S was built as part of the larger construction of the Golden State Freeway.  One of the CHPW articles I referenced certainly implies the project was likely constructed as a glorified off ramp from a chargeable I-5.  For one thing, 5S was for a time the interim mainline of I-5 to San Fernando Road.  Why that latter example is no longer a standalone state highway I don't understand. 


To be precise: This is not Route 40S (as it, a route in the database with an S suffix, such as I-5S or I-10S). It is Route 40, with a segment with S postmiles, where S means " Spur mileage of original or realign mileage". Perhaps a niggly difference, but we're a roadgeek community and embrace such differences. There is no suffixed Route 40.

According to the SHN Database ( ), the segment is:

OBJECTID   483   
Route   40   
RouteS   40   
PMRouteID   SBD040.S.L   
County   SBD   
District   8   
PMPrefix   S   
bPM   0   
ePM   0.794   
bPMc   S0.0   
ePMc   S0.794   
bOdometer   0   
eOdometer   0.794   
AlignCode   Left   
RouteType   Interstate   
Direction   WB   
Shape__Length   1,571.488   
Daniel - California Highway Guy ● Highway Site: ●  Blog: ● Podcast (CA Route by Route): ● Follow California Highways on Facebook:


So the point is that this piece of Main St is still a state highway? Ho hum. I wonder how many people actually use it for transitioning from I-40 WB to I-15 NB, or from I-15 SB to I-40 EB, given that you can save a lot of time taking Newberry, Riverside, and Harvard Rds, and staying out of Barstow entirely.

BTW, I see that Google labels that bit of Main Street as part of I-15 Business. But I always take Google's road identification with a grain box of salt.

Max Rockatansky

Depends on how you view it.  This segment of Main Street is a state maintained road which is actually longer than fully signed and independent state highways.  I can only speak for myself, but I enjoy digging on weird oddities in the state highway system.  The spur mileage and routes are some of the last frontiers left to cover for state highways left in California. 

And yes, Main in Barstow is signed as I-15 Business. 


Yes, I see that now in GSV. One thing I don't see is pentagonal county route 66 signs, although Google calls it that too. In California, can a piece of road be both a County Sign Route and a state highway? Or was SBD's fairly recent designation of the former an informal thing?

I do see a combination of I-15 Business Route signs, brown Historic US-66 signs, and Barstow US-66 signs on brick pedestals, through the downtown, but the first county route 66 sign I see is at Barstow Rd.

Max Rockatansky

There aren't many, but I can think of several examples of State Routes and County Routes being multiplexed.  J18/CA 165 east of Newman and A28/CA 3 in Montague come to mind.


Quote from: Max Rockatansky on February 10, 2024, 11:16:32 PM
There aren't many, but I can think of several examples of State Routes and County Routes being multiplexed.  J18/CA 165 east of Newman and A28/CA 3 in Montague come to mind.

CA 120 and J9/J14 in Oakdale if you want a double.
Please note: All posts represent my personal opinions and do not represent those of my employer or any of its partner agencies.

Travel Mapping (updated weekly)

Opinions expressed here on belong solely to the poster and do not represent or reflect the opinions or beliefs of AARoads, its creators and/or associates.