SuperSleeper,
I have posted pertaining to the same subject but a much more specific question. Anyway, the MKIV does not support RDC/TMC itself. In fact that has nothing to do with the Navigation system,it is actually the Radio module. As far as I know you must install a TMC device to your vehicle in order to receive the traffic information. The BM54 and possibly the BM53 business radio have the TMC built in. These can be purchased from bimmernav. The only question is will these actually work in the US? I don't know, maybe. Hopefully someon eelse can shed more light on this. I am sure as TMC becomes more readily available there will be more retrofit solutions.
------Kham