Wow, that's not good... A large Sedan from early 2000s driven well can easily beat that..
I regularly hear about small cars doing 70 mpg == 30km/L
My Toyota Yaris is not fuel efficient at 130 km/h on the highway, but it still manages 40mpg = 17 km/L
Of course, it's not SUV.. I basically decided against buy a big car until EVs are ready -- they are now, but that doesn't mean I should throw out my existing car :)
First off, if you're not in the US, make sure that you are converting from a US gallon, and not imperial gallon.
35 MPG (US gallons) = 6.72 Liters per 100 km
Any case, my car does roughly 17 megameters / meter^3 -- that's proper SI units :)
US cars are a bit bigger than european or asian models, so they are probably a bit heavier. Still, I think fuel efficiency is pretty optimized in all modern cars regardless of where you live.
But maybe that's only downhill -- I'm certainly not reaching it :)
But other mini cars like: https://en.m.wikipedia.org/wiki/Volkswagen_Lupo
Or so I hear...