The OP is right,
If you code in a Trip Planner route it has to fulfill each segment of the route before it will attempt the next segment.
You can manually send the Nuvi to the next waypoint by going into Trip planner on the Nuvi.
Traffic is innefective when using Planned Trips most of the time. Traffic is innefective most of the time anyway.
I can count on the fingers of one hand how many time traffic has helped me.