I don't know how TMC works in the rest of Europe but in the UK it definitely piggie backs onto an existing FM radio station and it is encrypted. You don't need to enter a code to decrypt it though, the nav unit manufacturers pay a licence fee and the decryption is enabled on all their TMC products.

http://en.wikipedia.org/wiki/Traffic_Message_Channel
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Remind me to change my signature to something more interesting someday