I am not American but I know this.

RDS is traffic information by radio announcement. When the radio station that broadcasts traffic information announces that info, it also broadcast a signal that activates RDS (or is RDS, I am not techncal either). Then the traffic announcement from that station is on speaker, whatever other radio station was playing or whatever sound source (like CD) is active. Everything else is interrupted and only traffic information, which is louder than normal sound, is active.

And TMC in the States needs, besides the correct settings, extra licenses I think, because AFAIK it's a normal paid service.
Not 100% sure, however.