TMC - Traffic Message Channel is a technology allowing to visualize traffic news on enabled devices. Information is transitted on FM radio frequencies, through the RDS channel and uses the TMC protocol which defines the codification rules.
Every traffic news is sent as an indipendent message.Messages are composed of an event code, a localization code and some more information, such as the expiry date. Messages are coded in Alert C and can be cripted, following the specifications defined in the TMC protocol.
The receiving system decodes the messages to show the traffic news on the map, using the TMC protocol and the localization tables, available in the maps by all major providers.
The device can also provide the traffic news in a text, translating it in the user language.
The TMC protocol is defined and mantained by TMC Forum.
You can find the Italian official location table on the site by the Italian Ministero dei Trasporti.