I've driven I-90 west out of Boston many times. Eventually you get to a bridge over the highway that is much higher than average, given my driving experience in the area. I won't attempt to estimate the height, but you can see in the link that it is well higher than a big rig.
https://www.google.com/maps/@42.2133217,-71.7753806,3a,45.7y,222.16h,83.73t/data=!3m6!1e1!3m4!1sKo6Q6QeK9JoZu6UqvUikuA!2e0!7i16384!8i8192!5m1!1e4
Further west, you come across the reverse situation: the interstate crosses a river and is well higher than the roadway along the bank.
https://www.google.com/maps/@42.1574415,-72.8151552,3a,75y,158.36h,77.1t/data=!3m7!1e1!3m5!1sgeiOwzG3I9hn9M8DTSG9bA!2e0!5s20180801T000000!7i13312!8i6656!5m1!1e4
What is the most extreme example of either (or both) of these scenarios? Examples that don't involve river beds would be especially intriguing.
In Google Earth, there's 3D imagery for that area, and you can see that the Park Hill Ave road surface is 48ft above the I-90 road surface, so subtract a few feet for the thickness of the bridge. That doesn't seem very high.
Major bridges are often very high, as they pass over other roads. The US record may be the New River Gorge Bridge in West Virginia, which is 876ft above the river, and looks like it's about 600ft above Fayette Station Rd, although the clearance to the arch is much less. But that's not an Interstate. There are a couple higher bridges in the US, but they don't pass over roads. The George Washington Bridge (I-95) looks like it's over 200ft above the parking lot on the NJ side. The Long Beach International Gateway bridge (I-710) is a couple hundred feet above Pier D St that runs next to the ship channel, and that's true clearance. One non-Interstate that doesn't involve water (although I'm sure there's a little creek in there somewhere) is the Cold Spring Canyon Bridge on CA-154 north of Goleta, which looks like it's a couple hundred feet above Stagecoach Rd, although there's an arch that reduces the clearance.
US 27 over I-275 near Newport, KY comes to mind.
https://goo.gl/maps/A18BPFQYDVZG6igh8
Muholland Drive over I-405 in LA is another.
https://goo.gl/maps/Hgm1fco27uzcuADa6
Clay's Ferry Bridge near Lexington Kentucky
SM-G996U
While technically not an Interstate, French A75 over D41 near Millau is what first came to mind :sombrero:.
I always think of this bridge over US 65 in Missouri. Not currently an Interstate, but it very well could be one day. It is not only really high above the highway, but it is an interesting looking bridge as well.
https://goo.gl/maps/MiXCxFZCSCzZGT577
There is one over the Ohio Turnpike in Eastern Ohio.
Existing 5-page thread on this: https://www.aaroads.com/forum/index.php?topic=8710.0