Most important interstate that isn't x0/x5

[Perfxion]

I-69 in Texas, one of the busiest highways stretches in the country. Might not be long(for now), but does move a lot of traffic in Houston.

[TEG24601]

I-94.  It's essentially an x0 but couldn't be numbered as such because they ran out of x0 numbers due to skipping 50 and 60.

Of Course, 94 should be 90, 90 from Gilette East should be 80, and extend to give Portland an x0.


I would say both 84s would qualify, as would 69, especially once it is completed.

[Darkchylde]

Maybe not most important, but I-12 is pretty important down in Louisiana, carrying a lot of long-haul traffic that's bypassing New Orleans. For an 85-mile Interstate, it's an extremely vital one.

[ilpt4u]

Maybe not most important, but I-12 is pretty important down in Louisiana, carrying a lot of long-haul traffic that's bypassing New Orleans. For an 85-mile Interstate, it's an extremely vital one.

Shoulda, Woulda, Coulda...

I-12 shouldn't exist. The Roadway should -- but it should either be an (even)10 3di, or it should be Mainline I-10, and the leg down to NOLA should be (even)10 3di -- but it is what it is. I-410 would be a just fine designation, for whichever segment one would choose to make the 3di

[hbelkins]

I-10 should stay on I-12, and the New Orleans segment of I-10 would make a nice I-6.

[plain]

^ I have mixed feelings about I-10 running through New Orleans. On one hand I can see where the interstate should have as many major cities on its route as possible as it's an I-x0 cross country interstate. On the other hand it deviates from its overall route across Louisiana to serve the NO.. that city was already major well before the interstate system was even thought of and it could've been served by another number. I actually like that I-6 recommendation though

[nexus73]

My comments weren't about a -current- rerouting of I-5, it was about previous comments about the -original- location of I-5, as to the question of why wasn't it routed within a band of about 5 miles on either side of CA-99.

Didn't realize your concept was retroactive to '57.  In either case, the Westside Freeway (as it was conceptually called in pre-Interstate days) had been a longstanding Division of Highways concept (since at least the immediate postwar time frame) as an efficient conduit between L.A. and the Bay Area.  US 99 through the major Valley cities & towns had been in a process of gradual upgrade since the late '30's, with full freeway sections through Galt, Manteca, Chowchilla, Tulare, and Delano fully deployed by the time the Interstate system was initiated in '56 (and the original Fresno freeway bypass was under construction as well).  The original concept was to simply route I-5 up US 99, expanding on what was already in place, and splitting into I-5E and I-5W in Modesto (the grading for the "split" interchange is still in place today!).  The Division of Highways saw the opportunity to get the direct LA-SF route built with 90% federal funds, so they petitioned to reroute I-5 over the Westside alignment, claiming that the projected AADT derived from interregional travel would at least offset that of the aggregate local and long-distance totals for the US 99 routing.  Despite the original stated Interstate system concept of connecting cities over 50K (and the 1955 census estimates showed both Bakersfield and Fresno exceeding that number), FHWA elected to relocate I-5 to the Westside alignment, much to the consternation of officials along the US 99 corridor.  The Division reassured these folks that even though the Interstate took the "beeline" metro-to-metro route to the west, they wouldn't be left out -- that US 99 would continue to be improved until it was itself a full freeway (which finally happened some 59 years later -- and 50 years after the U.S. shields were replaced!). 

To the Division of Highways, the I-5 location was a stark choice -- continue with what they were already doing along US 99, or take the most direct route possible -- where I-5 is today.  Although at that time there was sufficient land, mostly to the west of the 99 alignment, to deploy a route such as was suggested in the prior post, it would simply be a way to avoid a lot of in-town freeway mileage through the various Valley cities -- but still maintaining the basic 99 trajectory, laid out as it was along the original Southern Pacific rail line -- it wouldn't have "solved" the issue of the conception of I-5 as the aforementioned inter-metropolitan "beeline", but merely recasting the US 99 alignment to a new-terrain route a few miles away.  And that wasn't a choice even offered back in '57 -- it was 99 or the Westside -- period (this was 2 years prior to the conception of the omnibus California Freeway and Expressway system, which codified this and other statewide highway planning efforts).     

Thanks for the detailed explanation, that is what I was looking for, as to how CalTrans made the decision in the late 1950s.

However, as I pointed out, the mileage savings is insignificant, 2 miles out of 388 miles.  I-5 between Wheeler Ridge and Tracy goes thru areas of very low population, even today.

I-5 between Tracy and Sacramento is more of the idea that I had in mind, a new location routing within about 6 to 8 miles away from CA-99 that is a bypass but also close enough to provide access to the CA-99 corridor.

I just don't see the logic for how Caltrans routed I-5 between Wheeler Ridge and Tracy.  The "Westside Freeway" concept from the 1940s just doesn't seem to have any advantages over the CA-99 corridor.

Yeah -- it's ironic that as a LA-Sacramento route, there's scant mileage difference between the full I-5 route and the I-5/CA 99 alternative via Bakersfield and Fresno.  However, it does cut off several miles from the L.A. to San Francisco "inland" route (as opposed to US 101), which was nominally a combination of US 99, CA 120, and US 50.  In that context it must be noted that the original I-5 concept included service to and from the Bay Area (via the "split" of I-5W and I-5E); the selection of the Westside alignment was intended to emphasize that particular priority.  The decision to jettison the E/W designations in 1963 -- 17 years prior to AASHTO's policy change re suffixed Interstates -- was more due to the fact that this would have required a nearly 50-mile multiplex of I-80 and I-5W only a few miles from the west I-80 terminus; that was considered a bit awkward -- and happened at the same time that the Division of Highways was formulating plans to eliminate in-state multiplexes in general (as expressed in the next year's mass renumbering).  The elimination of both the suffixed routes and the long Interstate multiplex was simply the "first shot across the bow" of that entire process.

Interesting to think how much more awful the 99 corridor would be if I-5 used it in the Central Valley and all you had was 33 as the quasi alternate.  I-5 really does get a ton of truck/commuter off 99 already and its still congested as all hell.  I couldn't fathom how many lanes it would take to handle the traffic of both 99 and I-5 in the Central Valley today onto one route.....maybe 8 from Bakersfield to Fresno?

Exactamundo Max!  If it was up to me, I-5 in the San Joaquin Valley would be 4 lanes in each direction with a top speed of 85 MPH between the I-5/99 split and the I-580 interchange. 

Rick

[nexus73]

I-84 from PDX to I-80 east of SLC is the most important E/W route for the northwestern section of the USA that meets the no 0/5 test.

Rick

[sparker]

Thanks for the detailed explanation, that is what I was looking for, as to how CalTrans made the decision in the late 1950s.
However, as I pointed out, the mileage savings is insignificant, 2 miles out of 388 miles.  I-5 between Wheeler Ridge and Tracy goes thru areas of very low population, even today.
I-5 between Tracy and Sacramento is more of the idea that I had in mind, a new location routing within about 6 to 8 miles away from CA-99 that is a bypass but also close enough to provide access to the CA-99 corridor.
I just don't see the logic for how Caltrans routed I-5 between Wheeler Ridge and Tracy.  The "Westside Freeway" concept from the 1940s just doesn't seem to have any advantages over the CA-99 corridor.

Yeah -- it's ironic that as a LA-Sacramento route, there's scant mileage difference between the full I-5 route and the I-5/CA 99 alternative via Bakersfield and Fresno.  However, it does cut off several miles from the L.A. to San Francisco "inland" route (as opposed to US 101), which was nominally a combination of US 99, CA 120, and US 50.  In that context it must be noted that the original I-5 concept included service to and from the Bay Area (via the "split" of I-5W and I-5E); the selection of the Westside alignment was intended to emphasize that particular priority.  The decision to jettison the E/W designations in 1963 -- 17 years prior to AASHTO's policy change re suffixed Interstates -- was more due to the fact that this would have required a nearly 50-mile multiplex of I-80 and I-5W only a few miles from the west I-80 terminus; that was considered a bit awkward -- and happened at the same time that the Division of Highways was formulating plans to eliminate in-state multiplexes in general (as expressed in the next year's mass renumbering).  The elimination of both the suffixed routes and the long Interstate multiplex was simply the "first shot across the bow" of that entire process.

The I-580 connection to I-5 might have needed to be moved 8 or 10 miles to the west, but the overall distance difference would have been insignificant.  Maybe 10 miles longer than the current 383 miles between LA and SF.

As the diagonal part of I-580 just to the NW of the I-5 junction lies along the eastern fall line of the Coast Range, repositioning it west would have put it up into the mountains -- something Caltrans or its predecessor agency wouldn't do unless at the point of a gun; that would have required two Interstates (I-205 as the other) heading up into the hills, with an interchange close to the top of the Altamont summit.  The current triangular (5/580/205) arrangement around Tracy is probably the most optimal, considering the traffic patterns (most peak traffic coming EB on 580 remains eastbound on I-205, as that's the route that passes or leads to most of the areas than have become Bay Area commuter exurbs).  One of the alternatives considered between '57 and '59, after the Westside alignment had been selected, was to run I-5 a little farther up what's now I-580 and then curve it north through the east side of Tracy to a directional "T" interchange which would serve as the split point for I-5E and I-5W.  However, when the first iteration of the California Freeway & Expresway system was published in 1959, the current triangle was in place, including a continuation of the I-580 (then I-5W) trajectory as a future freeway (now CA 239).  The southwest side of the triangle was legislatively LRN 110 (the designation also applied to CA 132, which was the original I-5W route prior to the Westside relocation).

Just as well -- a single Tracy-bound I-5 alignment would have added some 12 miles to the LA-SF trip and 7-8 miles to LA-Sacramento; it certainly would have posed problems for the commute situation decades later!  With the mountains to the west and the San Joaquin Delta wetlands just to the north of Tracy, the "Tracy Triangle" is probably the best that any road-building agency could hope to do.       

[Beltway]

The I-580 connection to I-5 might have needed to be moved 8 or 10 miles to the west, but the overall distance difference would have been insignificant.  Maybe 10 miles longer than the current 383 miles between LA and SF.

As the diagonal part of I-580 just to the NW of the I-5 junction lies along the eastern fall line of the Coast Range, repositioning it west would have put it up into the mountains -- something Caltrans or its predecessor agency wouldn't do unless at the point of a gun; that would have required two Interstates (I-205 as the other) heading up into the hills, with an interchange close to the top of the Altamont summit.  The current triangular (5/580/205) arrangement around Tracy is probably the most optimal, considering the traffic patterns (most peak traffic coming EB on 580 remains eastbound on I-205, as that's the route that passes or leads to most of the areas than have become Bay Area commuter exurbs).  One of the alternatives considered between '57 and '59, after the Westside alignment had been selected, was to run I-5 a little farther up what's now I-580 and then curve it north through the east side of Tracy to a directional "T" interchange which would serve as the split point for I-5E and I-5W.  However, when the first iteration of the California Freeway & Expresway system was published in 1959, the current triangle was in place, including a continuation of the I-580 (then I-5W) trajectory as a future freeway (now CA 239).  The southwest side of the triangle was legislatively LRN 110 (the designation also applied to CA 132, which was the original I-5W route prior to the Westside relocation).
Just as well -- a single Tracy-bound I-5 alignment would have added some 12 miles to the LA-SF trip and 7-8 miles to LA-Sacramento; it certainly would have posed problems for the commute situation decades later!  With the mountains to the west and the San Joaquin Delta wetlands just to the north of Tracy, the "Tracy Triangle" is probably the best that any road-building agency could hope to do.       

If I-5 could have been routed about 6 to 8 miles west of Modesto, then it would have connected to I-205 about 2 miles west of the current I-5/I-205 junction.  It could be adjusted a bit due to topography, but we would be looking at 5 miles or so more for LA-SF and LA-Sac, which would not be significant for a ~388 mile trip.

I'm not really saying that anything is intrinsically wrong with the "super bypass" alignment, I just see no compelling reason for it, it is about 240 miles and 26 interchanges in an area with very little population.

[kkt]

Even today the I-5 "super bypass" goes thru areas of very little population that don't warrant an Interstate highway.
Why not route I-5 within a band of about 5 miles on either side of CA-99?  That way it would take advantage of being a new location highway with the most modern design standards, being a bypass of CA-99, and being in relative proximity to the populated areas along CA-99.

Even the relatively large central valley towns are still small compared to the metropolises of the S.F. Bay Area and greater L.A.  I-5 is a shorter distance between them, so it would remain the preferred route for through traffic even in CA 99 were completely upgraded.

Six lanes is a pretty big reach for CA 99.  It would be a lot more cost effective to make CA 99 four lanes with geometric design appropriate for an interstate, and instead upgrade I-5 to six lanes.  Most of I-5 was designed with some growth space.

Los Angeles to Sacramento is 386 miles via I-5 alone
Los Angeles to Sacramento is 388 miles via CA-99 north of Wheeler Ridge

Oakland to L.A. via I-580 and I-5: 372 miles
Oakland to L.A. via I-580, I-205, CA 120, CA 99, I-5: 396 miles

It's about a faster route between the major metropolises.

[Beltway]

Los Angeles to Sacramento is 386 miles via I-5 alone
Los Angeles to Sacramento is 388 miles via CA-99 north of Wheeler Ridge

Oakland to L.A. via I-580 and I-5: 372 miles
Oakland to L.A. via I-580, I-205, CA 120, CA 99, I-5: 396 miles
It's about a faster route between the major metropolises.

I get 383 and 404 miles respectively between S.F. and L.A.
That is still only 5.1% difference.

There are significant direction changes on that segment of CA-99, so a straighter "near western" I-5 bypass of CA-99 could have been devised that might have cut 5 or 10 miles off of that 404 miles.

[sparker]

Los Angeles to Sacramento is 386 miles via I-5 alone
Los Angeles to Sacramento is 388 miles via CA-99 north of Wheeler Ridge

Oakland to L.A. via I-580 and I-5: 372 miles
Oakland to L.A. via I-580, I-205, CA 120, CA 99, I-5: 396 miles
It's about a faster route between the major metropolises.

I get 383 and 404 miles respectively between S.F. and L.A.
That is still only 5.1% difference.

There are significant direction changes on that segment of CA-99, so a straighter "near western" I-5 bypass of CA-99 could have been devised that might have cut 5 or 10 miles off of that 404 miles.

As they say, true that!.  The particular alignment of the Westside/I-5 freeway was selected to avoid much of the more valuable land owned by the various large-scale agribusinesses that dominate Valley commerce.  An effective "straight-line" alignment avoiding the mountains and intersecting (then) US 50 west of Tracy would have passed east of Los Banos and Huron -- but it would also have cut through the historic Tulare Lake bed southwest of Corcoran (which essentially re-formed back during the 1997 regional flooding).  It's more than likely that any "quasi-Westside" alignment in between the current I-5 route and the US/CA 99 corridor would have drawn considerable political opposition from very influential landowners; the basic Westside alignment was something that had been worked out in the postwar years; the advent of the Interstate system gave the Division of Highways the opportunity to deploy a "relief route" for 99, which was even then inundated with both agricultural and interregional commercial traffic.  And while the actual mileages show only a marginal difference between the travel distances from both Sacramento and San Francisco vis-a-vis L.A., it was also conceived as an effective doubling of overall capacity regarding the N-S Valley arterials (there's a reason I-5 is mostly 8 lanes south of Wheeler Ridge!).  The Westside -- as far as alignment is concerned -- was a "done deal" well prior to the granting of Interstate status.  And since in 1957 Bakersfield, Kingsburg/Selma, Merced, Livingston, Turlock, and Modesto still lacked freeway or even expressway bypasses, the shift of I-5 to the west was a relatively easy sell to everyone who didn't reside or have business along the 99 corridor -- the fact that it went through a lot of nothing was in fact one of the great marketing points of the concept -- less likelihood that over time development would overtake the efficiency of the route.   
   

[kkt]

Los Angeles to Sacramento is 386 miles via I-5 alone
Los Angeles to Sacramento is 388 miles via CA-99 north of Wheeler Ridge

Oakland to L.A. via I-580 and I-5: 372 miles
Oakland to L.A. via I-580, I-205, CA 120, CA 99, I-5: 396 miles
It's about a faster route between the major metropolises.

I get 383 and 404 miles respectively between S.F. and L.A.
That is still only 5.1% difference.

There are significant direction changes on that segment of CA-99, so a straighter "near western" I-5 bypass of CA-99 could have been devised that might have cut 5 or 10 miles off of that 404 miles.

I measured from Oakland, as the transportation and industrial center of the Bay Area. 

[Flint1979]

Maybe not most important, but I-12 is pretty important down in Louisiana, carrying a lot of long-haul traffic that's bypassing New Orleans. For an 85-mile Interstate, it's an extremely vital one.

It could have very easily been a child of I-10.

[Beltway]

I get 383 and 404 miles respectively between S.F. and L.A.
That is still only 5.1% difference.
There are significant direction changes on that segment of CA-99, so a straighter "near western" I-5 bypass of CA-99 could have been devised that might have cut 5 or 10 miles off of that 404 miles.

As they say, true that!.  The particular alignment of the Westside/I-5 freeway was selected to avoid much of the more valuable land owned by the various large-scale agribusinesses that dominate Valley commerce.  An effective "straight-line" alignment avoiding the mountains and intersecting (then) US 50 west of Tracy would have passed east of Los Banos and Huron -- but it would also have cut through the historic Tulare Lake bed southwest of Corcoran (which essentially re-formed back during the 1997 regional flooding).  It's more than likely that any "quasi-Westside" alignment in between the current I-5 route and the US/CA 99 corridor would have drawn considerable political opposition from very influential landowners; the basic Westside alignment was something that had been worked out in the postwar years; the advent of the Interstate system gave the Division of Highways the opportunity to deploy a "relief route" for 99, which was even then inundated with both agricultural and interregional commercial traffic.  And while the actual mileages show only a marginal difference between the travel distances from both Sacramento and San Francisco vis-a-vis L.A., it was also conceived as an effective doubling of overall capacity regarding the N-S Valley arterials (there's a reason I-5 is mostly 8 lanes south of Wheeler Ridge!).  The Westside -- as far as alignment is concerned -- was a "done deal" well prior to the granting of Interstate status.  And since in 1957 Bakersfield, Kingsburg/Selma, Merced, Livingston, Turlock, and Modesto still lacked freeway or even expressway bypasses, the shift of I-5 to the west was a relatively easy sell to everyone who didn't reside or have business along the 99 corridor -- the fact that it went through a lot of nothing was in fact one of the great marketing points of the concept -- less likelihood that over time development would overtake the efficiency of the route.   

The late 1940s would still have been in the Interstate era, the first route approval package was in 1947 even though no funding was authorized then.

"On August 2, 1947, Commissioner MacDonald and Federal Works Administrator Philip B. Fleming announced selection of the first 37,700 miles. The routes had been proposed by the State highway agencies and reviewed by the Department of Defense. However, neither the 1944 act nor later legislation in the 1940's authorized funds specifically for the Interstate System. As a result, progress on construction was slow."
https://www.fhwa.dot.gov/programadmin/interstate.cfm

The entire CA-OR-WA I-5 corridor would undoubtedly have been included, even though numbers weren't assigned then.

Very little stood in the way of rural Interstate construction back in 1950s and 1960s, and with many Interstates they crossed to the other side of the pre-existing highway when needed to avoid something.

There is very little online about this alignment, and it would be interesting to see the official location report that the DOT would have produced back then.

"1963
Westside Freeway (1-5): The 321-miles-long Westside Freeway was the longest freeway project undertaken by the State at that time on entirely new alignment. In addition, due to coordination with the California Aqueduct Project, the project required a close collaboration and development of new engineering technologies with Department of Water Resources and the Federal Bureau of Reclamation."
http://www.dot.ca.gov/hwy50/

[sparker]

Definitely part of the appeal, at least to the Division of Highways, was the proximity of the 5/Westside freeway to the nascent California Aqueduct project; much of the northern third of the route is immediately adjacent to the canal.  And as the two most prominent public-works contractors of the era, Atkinson and Teichert, were the principal contractors of both projects (Sacramento-based Teichert in the north and L.A.-based Atkinson for the southern reaches), some semblance of construction coordination was able to be reached (not that such translated into actual cost-cutting at the public funding level, but simply meant shared resources within the scope of the parallel projects). 

From discussions with Division/Caltrans personnel (several of which are family members), there was an internal timetable within the agency as to just how quickly the main corridor (5 from Wheeler Ridge to the 580 split and 580 north from there to [then] US 50 at Altamont) could be built and opened.  As it turned out, that was a bit over 12 years, from the beginning of grubbing in 1959 (the segment between CA 152 and US 50, not surprisingly the first to be opened to traffic six years later) to the final Westside segments being opened in early 1972.  Even taking into consideration the chargeable funding availability then, it's difficult to imagine a 300+ mile new-terrain route going from unimproved land to full facility in that period of time today.  The Division/Caltrans had no illusions about the timeframe of I-5 north of the Westside because of the San Joaquin/Sacramento delta wetlands that it encountered -- which it why it took an additional 9 years to finish off the remaining 70-odd miles into Sacramento. 

[Beltway]

Definitely part of the appeal, at least to the Division of Highways, was the proximity of the 5/Westside freeway to the nascent California Aqueduct project; much of the northern third of the route is immediately adjacent to the canal.  And as the two most prominent public-works contractors of the era, Atkinson and Teichert, were the principal contractors of both projects (Sacramento-based Teichert in the north and L.A.-based Atkinson for the southern reaches), some semblance of construction coordination was able to be reached (not that such translated into actual cost-cutting at the public funding level, but simply meant shared resources within the scope of the parallel projects). 

If it was anything like most Interstate projects back then, there would have been many construction contracts averaging 5 miles or so in length, and many different prime contractors.

There are considerable differences in highway engineering and highway construction, as compared to canal aqueducts.  I don't really understand the DOT's claim that there was a synergy between the two projects.

From discussions with Division/Caltrans personnel (several of which are family members), there was an internal timetable within the agency as to just how quickly the main corridor (5 from Wheeler Ridge to the 580 split and 580 north from there to [then] US 50 at Altamont) could be built and opened.  As it turned out, that was a bit over 12 years, from the beginning of grubbing in 1959 (the segment between CA 152 and US 50, not surprisingly the first to be opened to traffic six years later) to the final Westside segments being opened in early 1972.  Even taking into consideration the chargeable funding availability then, it's difficult to imagine a 300+ mile new-terrain route going from unimproved land to full facility in that period of time today.   

Many 300+ mile state Interstate corridors were built from scratch within 12 years back then.  It was a function of the prevailing cost of new rural Interstate highways of about $1 million per mile, the amount of revenue generated by the 4 cent per gallon federal gasoline tax, the lower level of prevailing population densities back then for rural areas, and the lack of any requirement for an NEPA EIS study.

The Division/Caltrans had no illusions about the timeframe of I-5 north of the Westside because of the San Joaquin/Sacramento delta wetlands that it encountered -- which it why it took an additional 9 years to finish off the remaining 70-odd miles into Sacramento.

Also took advantage of the fact CA-99 between Manteca and Sacramento was already a full freeway, thus lessoning the urgency as compared to south of there.

[sparker]

Definitely part of the appeal, at least to the Division of Highways, was the proximity of the 5/Westside freeway to the nascent California Aqueduct project; much of the northern third of the route is immediately adjacent to the canal.  And as the two most prominent public-works contractors of the era, Atkinson and Teichert, were the principal contractors of both projects (Sacramento-based Teichert in the north and L.A.-based Atkinson for the southern reaches), some semblance of construction coordination was able to be reached (not that such translated into actual cost-cutting at the public funding level, but simply meant shared resources within the scope of the parallel projects). 

If it was anything like most Interstate projects back then, there would have been many construction contracts averaging 5 miles or so in length, and many different prime contractors.

There are considerable differences in highway engineering and highway construction, as compared to canal aqueducts.  I don't really understand the DOT's claim that there was a synergy between the two projects.

From discussions with Division/Caltrans personnel (several of which are family members), there was an internal timetable within the agency as to just how quickly the main corridor (5 from Wheeler Ridge to the 580 split and 580 north from there to [then] US 50 at Altamont) could be built and opened.  As it turned out, that was a bit over 12 years, from the beginning of grubbing in 1959 (the segment between CA 152 and US 50, not surprisingly the first to be opened to traffic six years later) to the final Westside segments being opened in early 1972.  Even taking into consideration the chargeable funding availability then, it's difficult to imagine a 300+ mile new-terrain route going from unimproved land to full facility in that period of time today.   

Many 300+ mile state Interstate corridors were built from scratch within 12 years back then.  It was a function of the prevailing cost of new rural Interstate highways of about $1 million per mile, the amount of revenue generated by the 4 cent per gallon federal gasoline tax, the lower level of prevailing population densities back then for rural areas, and the lack of any requirement for an NEPA EIS study.

The Division/Caltrans had no illusions about the timeframe of I-5 north of the Westside because of the San Joaquin/Sacramento delta wetlands that it encountered -- which it why it took an additional 9 years to finish off the remaining 70-odd miles into Sacramento.

Also took advantage of the fact CA-99 between Manteca and Sacramento was already a full freeway, thus lessoning the urgency as compared to south of there.

California rural freeway contracts back in those days ('50's through the mid-70's) were a bit longer than 5-mile chunks; IIRC the average contract was between 15 and 20 miles for the I-5/Westside project, with some exceeding 40 miles (particularly the segment between CA 198 and CA 152, which was the most difficult to "stage", being the farthest from existing material/labor resource bases).  South of the Coalinga area, much of I-5 (save the Kettleman Hills segment) fit neatly as a diagonal laid across the existing grid pattern of farm roads; access to the construction site(s) was a relatively simple matter.  The portion north of CA 152 was sited right at the east Coast Range fall line parallel to existing CA 33; access was again thus simplified (a decent number of lateral roads).  The "synergy" with the parallel construction of the aqueduct was simple equipment and "staging" redundancy; the field materiels and equipment yards could be sited adjacent to one another (particularly if the primary contractor was the same for both projects).  Construction equipment could be shifted between the projects as needed -- saving the need to schlep stuff out from the corporate yards. 

I-5 was completed north to Stockton in the summer of '72; Charter Way (CA 4 & CA 26 at the time) was signed as "Temporary I-5" over to CA 99, which was likewise signed from there to the (then) I-80/US 50 "Oak Park" interchange in Sacramento.  The "W-X" section of the E-W freeway (then I-80, now US 50) also was signed as "Temporary I-5" over to the completed I-5 alignment east of the Sacramento River, completing the detour.  This arrangement continued until early 1981, when I-5 was completed from Stockton to Sacramento (after multiple drainage-related delays).   

[OracleUsr]

Definitely I-94.  Connects several of the mid-west's largest cities and continues onto I-90 to connect Seattle.

[Beltway]

There are considerable differences in highway engineering and highway construction, as compared to canal aqueducts.  I don't really understand the DOT's claim that there was a synergy between the two projects.

California rural freeway contracts back in those days ('50's through the mid-70's) were a bit longer than 5-mile chunks; IIRC the average contract was between 15 and 20 miles for the I-5/Westside project, with some exceeding 40 miles (particularly the segment between CA 198 and CA 152, which was the most difficult to "stage", being the farthest from existing material/labor resource bases).  South of the Coalinga area, much of I-5 (save the Kettleman Hills segment) fit neatly as a diagonal laid across the existing grid pattern of farm roads; access to the construction site(s) was a relatively simple matter.  The portion north of CA 152 was sited right at the east Coast Range fall line parallel to existing CA 33; access was again thus simplified (a decent number of lateral roads).  The "synergy" with the parallel construction of the aqueduct was simple equipment and "staging" redundancy; the field materiels and equipment yards could be sited adjacent to one another (particularly if the primary contractor was the same for both projects).  Construction equipment could be shifted between the projects as needed -- saving the need to schlep stuff out from the corporate yards. 

The requirements for an optimum alignment for a particular highway, as compared to the optimum alignment for an aqueduct system, are not necessarily the same and can easily be quite different.

Locating this aqueduct system as far west in the valley as possible, put it in the most rural land and (I would surmise) took the best advantage of topography for the siting of reservoirs and for reducing channel grades and pumping station needs as much as possible.

A very different set of requirements than what would be the best place to put an Interstate highway, regardless of the issue of synergy between the two projects.

"Super bypass" Interstate highway routes are rare, I can think of only three, this segment of I-5, the entire I-57, and I-80 across PA and NJ. 

In the case of I-80 a book was produced and I have a copy of it, _The Story of the Keystone Shortway_, by Keystone Shortway Association, 1970.  It goes into a lot of detail about the decision process and benefits, in sum a major mileage reduction over the turnpikes in the New York/Chicago route, plus the fact that 10 rural counties in PA strongly lobbied for the route for economic development.

I don't know of anything in detail published about the I-5 westside route, it would be nice to have.

[sparker]

I don't know of anything in detail published about the I-5 westside route, it would be nice to have.

Try to access past copies of California Highways & Public Works, the Division of Highways "house organ" journal published from the 1920's through the beginning of 1967 (and one of the first things cut by the incoming Reagan gubernatorial administration).  Multiple articles regarding the selection of the alignment of the Westside Freeway and how it related to the (often) adjacent California Aqueduct project.  Since publication ceased during the time period that I-5 was being constructed, the articles related to the construction project itself are limited; most of what saw print dealt with the preliminary planning phases and the first segments to be opened (those north of CA 152).  But good reading for anyone interested in the whole process.

While it's true that aqueducts and freeways have their own individual criteria, the juxtaposition of I-5 and the CA aqueduct north of CA 152 was because the intake for the aqueduct was sited on a branch slough of the San Joaquin River north of Tracy, and the aqueduct's pathway coincidentally mimicked that of the freeway, since the aqueduct system included the San Luis reservoir directly south of CA 152 and a few miles west of I-5, which is part of the system that "siphoned" off some of the aqueduct's water to serve the far reaches of the South Bay (Gilroy, Hollister, San Juan Bautista, etc.) as well as providing a "holding tank" for excess water in rainy years.  In order to serve that reservoir (water was emptied into the reservoir's "forebay" downgrade from the dam itself and pumped into the main reservoir as needed), the aqueduct path needed to stay as close to the mountain fall line as possible to remain elevated above the valley floor (to avoid having to install multiple pumping stations along the way -- since the water flow was south -- which in the SJ valley, meant slightly uphill).  The initial segment of the aqueduct was some 350 feet above the valley floor; Delta water was pumped uphill to this facility, and the subsequent waterway was all slightly downhill to the San Luis forebay.  The economics of the whole water project was predicated upon a minimum of pumping facilities -- just those needed to overcome mountainous topography.  And since part of the I-5 design criteria took it off the valley floor in the northerly stretches, it was only natural that the facilities paralleled each other rather closely. 

[Beltway]

I don't know of anything in detail published about the I-5 westside route, it would be nice to have.

Try to access past copies of California Highways & Public Works, the Division of Highways "house organ" journal published from the 1920's through the beginning of 1967 (and one of the first things cut by the incoming Reagan gubernatorial administration).  Multiple articles regarding the selection of the alignment of the Westside Freeway and how it related to the (often) adjacent California Aqueduct project.  Since publication ceased during the time period that I-5 was being constructed, the articles related to the construction project itself are limited; most of what saw print dealt with the preliminary planning phases and the first segments to be opened (those north of CA 152).  But good reading for anyone interested in the whole process.

Looks like they have been online since 2013 ... perhaps you could find the articles.
http://www.americanroads.us/forum/index.php?topic=249.0

While it's true that aqueducts and freeways have their own individual criteria, the juxtaposition of I-5 and the CA aqueduct north of CA 152 was because the intake for the aqueduct was sited on a branch slough of the San Joaquin River north of Tracy, and the aqueduct's pathway coincidentally mimicked that of the freeway, since the aqueduct system included the San Luis reservoir directly south of CA 152 and a few miles west of I-5, which is part of the system that "siphoned" off some of the aqueduct's water to serve the far reaches of the South Bay (Gilroy, Hollister, San Juan Bautista, etc.) as well as providing a "holding tank" for excess water in rainy years.  In order to serve that reservoir (water was emptied into the reservoir's "forebay" downgrade from the dam itself and pumped into the main reservoir as needed), the aqueduct path needed to stay as close to the mountain fall line as possible to remain elevated above the valley floor (to avoid having to install multiple pumping stations along the way -- since the water flow was south -- which in the SJ valley, meant slightly uphill).  The initial segment of the aqueduct was some 350 feet above the valley floor; Delta water was pumped uphill to this facility, and the subsequent waterway was all slightly downhill to the San Luis forebay.  The economics of the whole water project was predicated upon a minimum of pumping facilities -- just those needed to overcome mountainous topography.  And since part of the I-5 design criteria took it off the valley floor in the northerly stretches, it was only natural that the facilities paralleled each other rather closely. 

I much agree with all those design criteria up to the last sentence.  Move the water toward the populated areas with as much natural flow as possible, reduce the need for pumping facilities as much as possible; IOW water does need to go "uphill" at certain points to clear higher areas, but reduce total elevation changes as much as possible.

However the routing of I-5 is no more directly related to that of the aqueduct system than the routing of CA-99 is directly related to that of the aqueduct system.

[paulthemapguy]

I-94 should have been the northernmost x0 (so I-90), but you know, that whole problem of having to dodge the US Highways in the middle of the country.  The answer is I-94 thread over lol

[RobbieL2415]

QC Prov. HWY 15 and I-87.  Essentially connects Montreal to the East Coast.