It’s used by everyone in informal communication, but you won’t find it on road signs. (You might find it on the occasional ski track sign and such though.)
11.2 is easier to communicate than 0.112, it’s even easier than 1.12. As long as everyone uses the same scale you don’t have to write L/100km everywhere either, and then 11.2 takes less space (not less than 1.12, but us Norwegians have that 10km bias that other Europeans lack and we don’t get a say in Eu decisions)
Interesting - and I can see the point. However, I suspect there’s simply too many such words with long histories in the English language (footage, yardage, tonnage, acreage) to be able to impose a subsequent scientific criteria.
It also simply makes sense in the context - nobody really needs to know how much fuel a car burns over one km, but they need to know how much it burns over a 100km journey.