Ditto a short stretch shared by I-77 and I-81 in southwestern Virginia where you are simultaneously going north on one and south on the other.
Back in the 60s the highway planners here in the Phoenix metro decided they didn’t need no stinkin’ freeways – the surface streets will serve just fine. After a while they realized their mistake and we now have two, I-10 and I-17. The two of them intertwine around downtown, following the usual urban renewal meme of knocking poor folks’ homes, so they form a sort of minibeltway.
Didn’t help much. During rush hour there’s not much point in using the HOV lanes are about as jammed as the regular lanes.
There are various nerdy details having to do with history and funding, but for practical purposes of driving on them, probably the biggest difference is that interstates are all controlled-access. That is, the only way to get on or off of them is by ramp. There are no stoplights, intersections, railroad crossings, etc. This is designed to facilitate high-speed travel.
Many parts of the US Highway system are built to the same standard, and there are places where US highways are physically indistinguishable from interstates. But this is not a requirement, and there are a lot of areas where it’s not the case. In rural areas a US highway might be the main street through town, and will have stop signs, traffic lights, and even houses or businesses right along the highway.
Interstates will bypass smaller towns, and even when they go through cities you will still use an entrance or exit ramp to get on or off. US highways still serve many of the smaller cities and towns, and often provide important regional access routes.
As huge of a highway and central to the Dallas area as it is, it’s still just US-75 north of downtown Dallas (it’s I-45 south of there to Galveston). I guess because north of Dallas, it doesn’t actually go anywhere considered very “big-time”- Tulsa, Topeka, Omaha, Sioux City, Sioux Falls and Fargo are the biggest cities north of Dallas that US-75 passes through.
I suppose they could have/could still label it I-45 all the way up, but there’s no real push that I’m aware of to do so.
Sure, but that’s more a quirk of geography rather than a measure of the city’s importance. Austin is maybe 80 miles north of San Antonio on I-35, and it almost surely made more sense when the interstates were being built to send I-10 from Houston to San Antonio, because it was a better hub point for other highways/railways already, and because it was a considerably larger city at the time. Austin has only been “big” since the tech boom of the mid-late 1990s. Prior to that, it’s only claims to fame were being the state capital and having UT, and it was a town of 500k. San Antonio has for centuries, been the primary city in that part of the US/Mexico.
So in a sense, Austin got bypassed in favor of San Antonio, and there’s just nowhere but little towns to the east and west for a long way. They might want to eventually make US-290 from Houston to Austin an in-state interstate, but so far it hasn’t been an issue.
Well said. It is interesting that the second largest US state (by population) has no interstate between its largest city and its capital. I wonder how much further north Austin would have to have been located (in an alternate universe) in order to have gotten its own interstate — or, conversely, how much further south it would have to be, to have had the existing interstate deviate from the straight Houston-San Antonio path and pass through Austin.
Much like the way I-35 is split between east and west in DFW and Minneapolis/St. Paul, in a perfect world, they could split I-10 north through Austin and south through San Antonio.
Then there are the state capitals without an interstate connection: Pierre, SD; Dover, DE; Juneau, AK; Jefferson City, MO.
Sure, but the Denton / Hillsboro split section of I-35 is only about 90 miles.
To do what you’re describing is essentially naming US-290 as I-10N, and the existing Houston-San Antonio stretch as I-10S. Both are somewhere in the neighborhood of 250-300 miles.
I think the main issue is that 290 is really used for 3 main purposes - Houston/Austin, Houston/College Station, and Austin/Fredericksburg. There’s VERY little Houston/Fredericksburg traffic really, and it’s kind of a wash whether you go I-10 through San Antonio, or 290 through Austin anyway. The Houston/College Station part is pretty much already interstate-quality, so it just leaves the Hempstead/Austin leg that needs a bit of work, most of which would be bypassing smaller towns with streetlights (Giddings, I’m looking at you).
I think a lot of the reason Houston and Austin aren’t connected by interstates is due to the fact that it’s so close to San Antonio that is, and that 290 is adequate for the relatively limited amount of traffic between the two. I’d be willing to bet that a significant chunk of Houston/Austin traffic is related to UT football in the fall, if that gives you an idea of the level of traffic on that stretch of road.
I’m of the opinion that this fact, though not exactly common, is not rare, and pops up more often than one at first might think. I-41 & I-43 in the south Milwaukee suburbs is another example.
This has actually been mentioned numerous times on this board (I think even earlier in this thread?). In this case, it comes about as an artifact of the re-numbering of an existing freeway: What used to be State Route 17 ran from Santa Cruz, through Berkeley, Richmond all the way to San Rafael. The portion from Berkeley to San Rafael was made part of the Interstate system and re-numbered to be I-580, which now runs from the San Joaquin Valley to San Rafael. The portion of this that runs through Berkeley is also (and has always been) part of I-80.
Here is a sampling of some prior mentions:
Well, at least none of those prior mentions were from me and I’m not guilty of repeating myself. 
Then there’s U.S. Route 19 Truck, which has a wrong-way concurrency with itself.
And until fairly recently they all crossed the Mississippi on the same damned bridge. Who the hell thought that was a good idea? Even with 70 now going over the Musial bridge, the PSB is still a horrorshow.