In reply to:

except for the EON, which generally keeps you tuned in to the same station as you travel up and down our compact land.


EON (Enhanced Other Networks) makes the local TA work when you're tuned to a national BBC station. Every time a traffic announcement is triggered in a BBC local radio station the trigger is sent down to Broadcasting House and the appropriate message is sent out on the national network NICAM tribs. These can then be decoded at the local transmission station and the appropriate RDS flag triggered on the local RDS encoder.
It's actually AF that keeps the radio tuned in.
_________________________
Cheers,

Andy M