I’d always seen a red coloured “TMC” on the bottom of the sat nav screen and wasn’t really sure what it meant. It’s not until I upgraded the sat nav box that the TMC turned green which prompted me to find out more about what it does / means.
Traffic Message Channel (TMC) is a technology for delivering traffic and travel information to motor vehicle drivers. It is digitally coded using the ALERT C or TPEG protocol into Radio Data System (RDS) carried via conventional FM radiobroadcasts. It can also be transmitted on Digital Audio Broadcasting or satellite radio. TMC allows silent delivery of dynamic information suitable for reproduction or display in the user’s language without interrupting audio broadcast services.
More info at …… https://en.wikipedia.org/wiki/Traffic_message_channel
A thread on the 75&ZT OC forum explaining in more detail for our cars here …… https://the75andztclub.co.uk/forum/showthread.php?p=43716#post43716