If you have a unit like the nüvi 3790 or similar you can look in "[GPS drive]:\.System\TrafficProvider.xml".

Here's an example with extract of 2 entries from TMC providers in France:
Code:
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V-Trafic (FR):
FID=cc*256+sid=15*256+62=3902 REMARK: It's not always factor 256 for all FID calculations
PID=ltn1=30
RgnID=ltn2=32
VenID, use 1 for insert and 0 for remove

Via-Michelin (FR):
FID=cc*256+sid=15*256+58=3898 REMARK: It's not always factor 256 for all FID calculations
PID=ltn1=29
RgnID=ltn2=32
VenID, use 1 for insert and 0 for remove


Looking here in post #1 you can see the 2 code sets for France
Code:
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It was a year or two since I've tried this calculations. I don't have the complete calculations for all providers but this can be used as a starter for further investigations. The hardest to calculate would be the FID if you don't have a real 25-character unlock key to investigate with [Only registered and activated users can see links. ].


EDIT: Here's some more examples of my own previous investigations.

Sample calculation with Radio SI/TrafficNav (SI)
:Anim3: State Type of license Ltn 1 Ltn 2 SID
Radio SI/TrafficNav (SI) 9 1001 33 33 1
9=SL 1001 = lifetime
Formula Value
FID / MapID State*2^11+2^8+SID =9*2048+256+1 =18689 :Animated77:
PID =Ltn 1 =33
RgnID =Ltn 2 same as Ltn 1 =33
VenID (1=insert) (0=remove) 1

Sample calculation for Destia Traffic TMC (PL)
:111anim: State Type of license Ltn 1 Ltn 2 SID
Destia Traffic TMC (PL) 3 1001 5 5 2
3=PL 1001 = lifetime
Formula Value
FID / MapID State*2^11+2^11+2^9+2^8+SID =3*2048+2048+512+2 =8962 :Animated98:
PID =Ltn 1 =5
RgnID =Ltn 2 same as Ltn 1 =5
VenID (1=insert) (0=remove) 1

Maybe someone could find the pattern for generic calculation of FID values for TMC?