I drive a stretch of Interstate 75, between Lexington KY and Knoxville TN, every week. The first 17 miles in Tennessee are run along the top of a mountain ridge. While this makes for lovely views (albeit some of it is of strip mined mountaintops), the highway has several issues. There is frequent fog and ice, the trucks slow to a crawl going up the mountain (1000 foot elevatin gain in 4 miles), no truck lanes, rockslides, etc. There appears to be a perfectly serviceable valley just to the west which, had the highway gone that route, would have avoided a lot of these issues.
Second example: I-80 between Laramie and Rock Springs. The locals all told the highway planners that if they routed the highway over/near Elk Mountain, rather than following the existing US 30 route, it would close frequently due to the weather. They were right.
Aquiring highway rights-of-way is a tedious, difficult, complicated, and politically charged endeavor, in my experience. I bet that that no highway route is ever built exactly on the alignment which the transportation planners know is best.
There are, of course, many legitimate things to be avoided (floodways, archaeological sites, wetlands) and those pesky highway safety standards. Add property owners who don’t want to sell, and favors to be handed out to local politicians who just happen to own land somewhere close to the proposed roadway and you get some pretty crazy highway alignments.
I’ve seen a similar thing. Now, our population base means that Australia’s highways tend to be many decades behind US ones in standard. So the Great Western Highway west of Sydney was a case in point: it’s theoretically the road across the continent, but two and a half hours west of Sydney you’d be crossing a mountain range on two-lane (one each way) concrete slabs laid in the 1940s. The road was busy, and there were sharp, poorly-banked corners, limited overtaking opportunities, etc. In the late 1990s, they upgraded it to freeway standard. What happened? The proposed reductions in road fatalities didn’t eventuate because, although the road was wide and straight now, the lack of tree cover meant it was much more prone to “black ice” in winter.
Looking at the satellite view, it might be because they valley to the northwest of the I-75 ridge looks to be the only flat farm land in the area. That may have something to do with it.
Interstate 75 had to go up and over that ridge anyway in order to get to Knoxville. Might as well keep the road along the top of the ridge and out of the populated areas, especially since they were already up there.
When I interned in a Kentucky planning org, even demographic factors and impact on local business were considered. Are there small communities in the valley?
Maybe it’s like in “Good Omens,” where the demon Crowley messes up the highway plans to make a highway into a demonic symbol that screws up traffic, makes people angry, and generally contributes to chaos.
There is a story told of when they were planning the streets of Greenville, SC. Purportedly, the debates of construction were long and harried and finally the committee agreed to adjourn to one of the member’s houses for a homecooked dinner.
One of the members brought along drafting paper and had laid it out on the floor. The committee resumed their debate and in the heat of it all, much arm-waving and description ensued. The housewife walked by with a bowl of the remains of their spaghetti dinner - and it was inevitably struck by one of the waving arms and landed plop on the paper.
In desperation the chairman yelled, “Hold it right there!”
And thus the streets of Greenville, SC were designed.
A few - the area’s not well populated by any means. My own uneducated guess, in retrospect, is that an interstate might have gotten in the way of all the coal trucks coming down off the strip mines. There are roads throughout the mountains like that - you take your life in your hands driving along the northern valley of Kentucky’s Pine Mountain, for instance.
I drove that section of 75 on a non-stop run from Orlando to Cincinnati once. Yeah, it’s weird, and my ears popped a dozen times, but the views were nice.
You don’t usually see anything more interesting than accidents on interstates. I-95 might be the most boring stretch of road running through interesting places ever.