"Depuis quand on roule ?"
I'm not 100% sure on the meaning of the french sentence (maybe a native speaker can enlighten us a little). They either mean:
- 1) "Since when do we drive?" as almost a "WTF? Since when have we ever driven to the video store?" Meaning the speaker and his friend agreed to go rent a movie at the video store, and the speaker assumed that they would walk (as they always do), but the friend jumped into the car. To which the speaker reacted by saying "Since when do we drive?" In which case, your translation "since when have we been driving" does not work.
- 2) "Since when do we drive?" is being used incorrectly as an English translation, and it should be "How long have we been driving?". Meaning you and I are on a road trip from Montreal to Ottawa...roughly a 2 hour drive. After about an hour and a half you're getting tired and ask "How long have we been driving?" as an alternative to asking the dreaded "Are we there yet?" If this is what's meant by the French sentence, then your proposed "Since when have we been driving?" is correct, but to me sounds a little off. "What time did we start driving" or "how long have we been driving" sound better.
Hope that helps a bit!
Well as native speaker, both #1 and #2 are correct for this type of construction, but no for this specific sentence.
"Depuis quand on roule ?" means that the person asking is not driving the car herself/himself, that's why he/she doesn't use the word "conduire" to mean "drive".
But if it was about asking why we use a car to go somewhere, we would not use the verb "rouler" :
"Depuis quand on prend la voiture pour aller là-bas ?" = "Since when do we drive to go there ?"
That's what I meant. I hope it's clear enough.
The only difference I can see between the two is what I pointed out in suggestion #1. In that situation one could say "Since when have we driven?" but "Since when have we been driving?" doesn't work. Other than that context, the sentences do pretty much mean the exact same thing, and since Duolingo doesn't provide context, they should probably accept your translation.