RDS is the initialism for 'Radio Data System', it's used in all developed countries and is a method of embedding digital data silently into conventional FM radio sound broadcasts. It can be used for many sub-carrier uses and one of those is TMC, initialism for Traffic Message Channel. So, in a simplified way TMC is RDS or at least one important use of FM RDS and although more commonly used in FM RDS, Traffic Message Channels can also be found in Satellite Radio and DAB in UK, EU for example and Digital Radio in NA. A specifically enabled dual purpose or standalone receiver is required to receive and process the messages and give alerts. An example of an standalone receiver is a car charger/TMC receiver for GPS receivers such as TT and Garmin which will only receive and decode the TM Channels for which it's programmed.