You Cannot Use Traffic or TrafficTrends without a receiver.
TrafficTrends is supposed to learn the Traffic in your area and build some sort of a database that will help the Nuvi to calculate more efficient routes based on Historic Traffic Data.
It can only do this if you have a traffic receiver connected and a valid subscription to one of the traffic providers in your area (country).
I believe that traffic in the US is free if you are willing to put up with adverts. Maybe someone from the US can provide more info.
You Can also use traffic by means of SmartPhone Link if your Nuvi and Smartphone is supported and you have purchaced the subscriptions for your Country.