There’s a section of I-5 in California, between exits 176 and 183, where the Northbound and Southbound lanes cross over one another. Why? Anything having to do with giving one direction a grade advantage would, it seems to me, be exactly negated by the resulting grade on the other direction. I realize there’s some grade separation due to terrain, but that only explains the split, not the crossover, afaict. Is there (or was there expected to be, when they designed it) a lot more traffic in the one direction compared to the other?
Ariaona has a similar stretch, in this case of a divided 4-lane:
In this case, it was because of the terrain, and that the highway was initially a two-lane road. The land is irregular and rugged, and it seems that if the lanes continued to keep proper left-right arrangement at Rincon pass, that the northbound lanes would have a real sharp bend at that rock.
Perhaps I-5 has a similar design history.
Northbound I-5 in the vicinity of Castaic was originally US 99 and covered both directions. Presumably it was more cost-effective to lay the southbound lanes near Ridge Route Road, which dates to 1915, rather than with the northbound lanes.
‘You’re not from around here, are you?’ 
From Interstate Guide - Interstate 5:
The roadbeds are cut into the sides of the valley, I’ve always assumed they could only fit half the lanes on either side. It just so happens the west side of the valley has a shallower grade so they ran the up-hill traffic there, thus requiring these crossovers. It’s the Grapevine, sure, not Cabbage, but still, it’s the Grapevine.
So the reasoning was, better Northbound traffic have an easier grade on the way up than Southbound traffic having an easier grade down? I drive an old Volkswagen, and always found an easier slope down to be more desirable; a tough slope up might kill my engine, a tough slope down might kill me.
Oddly, I live near Castaic, where they cross over. It is odd, unless your on them, when you dont really notice it that much.
I’m depressed that I’ve been away long enough that “I-5” didn’t leap out at me as being horribly wrong. I was just back in LA last week and actually had to force the words “the 101” out of my mouth. I never should have moved away.
At any rate, I’d wondered about the reason for this myself, so it’s nice to have an answer. Certainly makes for an odd driving perspective.
Arizona is a weird hybrid. All those ex-Angelenos that come out here have infected the language, but not fully.
Here they talk about “The I-10”. That’s so painful to hear!
Also, who refers to exits by their number???
OP should have been, “On the Grapevine, there’s a part of the 5 between Parker Road and Templin Highway…” and then we would have known wtf he was talking about.
Nothing wrong with “I-5” . 
I clicked the link to make sure, but I knew right away what the OP meant … it’s something of a memorable sight right after the top crossover … the way the freeway is cut into the steep canyon walls down into a sea of yellow haze … with just the tops of buildings visible in the downtown area.
The vista all but speaks to you, loud and clear, should’ve took the 58 over to 395 and catch I-15 through the Inland Empire …
ETA: Yeah, “Eye Five” is very common here, I have to think about it if someone says “The Purple Heart Freeway” or whatever it’s “officially” called.
The post above yours addresses this. 
In the case of the beeline highway the downhill side of the crossover section is straighter and engineered for a much higher speed. If you’re caught off guard by a turn uphill you’re likely to be going slower to begin with and gravity will slow you faster than you can brake regardless of traction. Panic braking on the same turn at high speed downhill will just make a lot of tire smoke and put you in to or through the guard rail.
Exactly! You have to be specific with your questions!
Oh, you mean the “the” number SoCal 'thing".
Having lived in both, i can tell you it’s not that much a “thing” outside message boards. Sure in SoCal “the” is more common, and sometime given the accent, while in Norcal "the’ is use more rarely and rarely emphasized.
But it’s a “meh” all around, i was surprised that someone would post to "correct’ it as it certainly not wrong…either way.
I lived in Santa Barbara for two years, plenty long for me to develop a profound distaste this kind of California exceptionalism.
And, it’s not real. It’s blown way out of proportion. (well, it’s true, we rarely refer to exits by their numbers)
Right … that’s the “California Hwy 22 Garden Freeway Exit brought to you by Burger King”
No, you’re thinking of the Bette Midler Freeway.