3D Traffic vs Live Traffic using Android Phone

 

I just purchased a Nuvi 3490lmt. I understand it has lifetime 3d traffic. I am also getting an Android phone to use to connect to the "Smartphone Link" services.
What I can't find out is, what's the difference between the existing 3d traffic and the Live Traffic.
Does the Live Traffic cover secondary roads more? Does it add to the coverage of the 3D Traffic, or just replace it? I know it is considered a premium service for $19.99 a year.
If anyone has any information about the differences, I'd appreciate it.

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Don't let people know you're having fun...they'll try to stop it! Nuvi 3490lmt,Nuvi 880, GPSV, Etrex Venture HC, Nuvi 750