I've been there only once, but I can't remember the place. It is kind of tricky and not that easy to be found. I tried to post earlier but I was disconnected and it seems that my post is not here. Man you can pay at any time but before renewing your car registration. When you go for that they will ask you to clear all the violations that you got. First time I hear about the 10% thing, might be a new thing but never hear of it.

The guys are right as well as the Airport one is less crowded than the Khalifa branch. You can also pay for that in 'Giant Stores' or 'Villagio' as I remember. I saw an office there for the Traffic Department. There is also in 'Hammad Hospital' down there near the Parking area down there. It is empty all the time.

Good Luck