Why didn't I-5 go through Bakersfield, Fresno, and Modesto?

[NE2]

I doubt they cared about Interstate standards when approving routes in the 1950s.
http://cahighways.org/001-008.html#005

Many ask why the Westerly routing in the San Joaquin Valley was constructed. One poster on MTR noted that in 1965 or thereabouts, in response to a legislative request, the then California Division of Highways prepared a report on the effect of the Interstate system on California highway development. One important point noted in this report was that although both I-5 and Route 99 were planned for eventual development as freeways, I-5 had received artificially higher priority over Route 99 because it was funded as an Interstate and so attracted federal completion deadlines. This in turn meant that more resources were being devoted to I-5 even though it was projected to be far less busy than Route 99. This might imply that the Division had had the decision to build I-5 on an independent alignment wished on it–possibly by the Legislature, the Highway Commission, or even the B.P.R.–and would rather have chased the traffic on Route 99, possibly by building it as an Interstate, while leaving the facility now known as I-5 to be developed as a western relief route at some point in the relatively distant future.

[myosh_tino]

So the posted speed limit is now 55 mph truck, 70 mph car?  That seems like an excessive difference.

Yes.  In fact, it's been this way ever since the NMSL was repealed.

On roads with speed limits in excess of 55 MPH, 3+ axle trucks are limited to 55 MPH.  Instead of using the standard TRUCKS XX sign, California developed their own separate truck speed limit sign (R6-3 (CA)).

FWIW, any auto towing a trailer is also limited to 55 MPH and yes, it has it's own sign too (R6-4 (CA)).

[TheStranger]

One thing that just came to mind now:

Using Interstate funding for new terrain bypass corridor isn't unique to 5 & 99 in the valley - the practice was pretty much repeated with the completion of I-15 between Devore and Corona in the 1970s and 1980s (a full decade or so before the older ex-US 395 corridor that is now I-215 was fully converted to freeway), even though I-15 was originally planned for the Riverside/San Bernardino route (including being signed along today's 215 from I-10 to Devore in the 1960s).

[DTComposer]

Meanwhile, over on the I-5 corridor, I believe the focus currently is on high speed rail as a means of moving passengers between Los Angeles and the San Francisco Bay Area. There have been repaving jobs especially in Kern County over the last few years, but I am not aware of any pending capacity improvements on I-5 at least between Wheeler Ridge and Tracy.

This is a topic of discussion that comes up every once in a while up here in the S.F. Bay Area, typically around major holidays due to the sheer number of people who travel to and from the Los Angeles area.  Many want to see Caltrans add a 3rd lane in each direction but according to our traffic pundits like Gary Richards of the San Jose Mercury News, the cost of adding an additional lane from Tracy to the 99/5 interchange near the Grapevine is pretty steep.  From my personal experience driving I-5 between CA-152 and CA-46 a couple of times a year going to and from Las Vegas, I think a 3rd lane should be considered given the amount of truck traffic on I-5.  Either that or remove the 55 MPH speed limit for trucks (which isn't going to happen).

I don't see how it would be prohibitively expensive, unless he's just referring to the basic cost of several hundred miles of asphalt. The ROW is already there, the bridges are wide enough, the terrain is mostly flat.

How about even having a passing lane every 20 miles or so, and otherwise restricting trucks to the right lane?

I prefer using 99 in almost all cases. Mostly because the options for stopping are a lot better, but it's also more pleasant. 99 carries more local traffic while the cars on the Westside Freeway seem to almost all be going as fast as possible between the Bay Area and LA.

I do this trip four-six times a year. I usually use US-101 for on my way to L.A. (more stopping places with more choices, more scenic), which maybe adds 45 minutes to my trip (mostly because I spend more time during the stops (usually San Luis Obispo or Santa Barbara)). I'll use I-5 on the way back, though, simply because I want to get home.

The same was true when I was living in L.A. and going up to the Bay Area (again, several times each year).

[coatimundi]

How about even having a passing lane every 20 miles or so, and otherwise restricting trucks to the right lane?

YES, TRUCK RESTRICTIONS, PLEASE...
Seriously, I spend most of my drives on the I-5 trying to get around trucks before they hit another truck going 1mph slower and try to pass. I think enforcing the 55 limit would help immensely. I've seen trucks pass me while I'm going 75 on there.

I prefer using 99 in almost all cases. Mostly because the options for stopping are a lot better, but it's also more pleasant. 99 carries more local traffic while the cars on the Westside Freeway seem to almost all be going as fast as possible between the Bay Area and LA.

I do this trip four-six times a year. I usually use US-101 for on my way to L.A. (more stopping places with more choices, more scenic), which maybe adds 45 minutes to my trip (mostly because I spend more time during the stops (usually San Luis Obispo or Santa Barbara)). I'll use I-5 on the way back, though, simply because I want to get home.

The same was true when I was living in L.A. and going up to the Bay Area (again, several times each year).

Well, yeah, I prefer the 101 to go from LA to my house, particularly since I'm only a couple of miles from the 101. I was mainly talking about coming from Sac or going to Fresno, where you have to jog south a little on something. I don't think 99 is really a reasonable alternative for LA-Bay Area traffic. It adds a lot of mileage.

[myosh_tino]

Meanwhile, over on the I-5 corridor, I believe the focus currently is on high speed rail as a means of moving passengers between Los Angeles and the San Francisco Bay Area. There have been repaving jobs especially in Kern County over the last few years, but I am not aware of any pending capacity improvements on I-5 at least between Wheeler Ridge and Tracy.

This is a topic of discussion that comes up every once in a while up here in the S.F. Bay Area, typically around major holidays due to the sheer number of people who travel to and from the Los Angeles area.  Many want to see Caltrans add a 3rd lane in each direction but according to our traffic pundits like Gary Richards of the San Jose Mercury News, the cost of adding an additional lane from Tracy to the 99/5 interchange near the Grapevine is pretty steep.  From my personal experience driving I-5 between CA-152 and CA-46 a couple of times a year going to and from Las Vegas, I think a 3rd lane should be considered given the amount of truck traffic on I-5.  Either that or remove the 55 MPH speed limit for trucks (which isn't going to happen).

I don't see how it would be prohibitively expensive, unless he's just referring to the basic cost of several hundred miles of asphalt. The ROW is already there, the bridges are wide enough, the terrain is mostly flat.

I'll agree that there's plenty of ROW but I don't recall seeing too many bridges that, as constructed, are wide enough for a 3rd lane plus a standard left shoulder.  Keep in mind we're talking about constructing two lanes (one each way) over a distance of almost 240 miles.  A project of that scale will most certainly not be cheap.

[DTComposer]

Meanwhile, over on the I-5 corridor, I believe the focus currently is on high speed rail as a means of moving passengers between Los Angeles and the San Francisco Bay Area. There have been repaving jobs especially in Kern County over the last few years, but I am not aware of any pending capacity improvements on I-5 at least between Wheeler Ridge and Tracy.

This is a topic of discussion that comes up every once in a while up here in the S.F. Bay Area, typically around major holidays due to the sheer number of people who travel to and from the Los Angeles area.  Many want to see Caltrans add a 3rd lane in each direction but according to our traffic pundits like Gary Richards of the San Jose Mercury News, the cost of adding an additional lane from Tracy to the 99/5 interchange near the Grapevine is pretty steep.  From my personal experience driving I-5 between CA-152 and CA-46 a couple of times a year going to and from Las Vegas, I think a 3rd lane should be considered given the amount of truck traffic on I-5.  Either that or remove the 55 MPH speed limit for trucks (which isn't going to happen).

I don't see how it would be prohibitively expensive, unless he's just referring to the basic cost of several hundred miles of asphalt. The ROW is already there, the bridges are wide enough, the terrain is mostly flat.

I'll agree that there's plenty of ROW but I don't recall seeing too many bridges that, as constructed, are wide enough for a 3rd lane plus a standard left shoulder.

This is my recollection of a typical bridge over I-5:
https://www.google.com/maps/@35.8440688,-119.8240082,3a,75y,333.8h,89.74t/data=!3m6!1e1!3m4!1sjWVfUMIBg4IUPHY7qAR4ng!2e0!7i13312!8i6656!6m1!1e1
It seems to have enough room, but I'm not qualified to make an expert opinion on this. And you're right, there may very well be numerous bridges with less clearance than this.

Keep in mind we're talking about constructing two lanes (one each way) over a distance of almost 240 miles.  A project of that scale will most certainly not be cheap.

I didn't meant to imply otherwise - the tone of the original comment made it seem like there was reason to think it would be more expensive than an average project of this scale.