Insulation, Radiant and Vapor Barriers - Sound Insulation

Hi,

I live in a 10 year old house. I'm currently upgrading the trim - adding new base,crown, window casing etc. Our den faces a freeway that is about 2 miles away. The noise is not that bad but since I will have limited access to the wall space I thought I would ask about the possibility of adding sound deadener. The house framing is 2x6 and there is insulation in the walls. The room also has a large Viking double pane window (typical builder grade window). Exterior of hosue is stucco. So a few basic questions first -

1. With the window I described, how much sound transmits via the windows vs. the walls? The window has a metal frame. I would entertain replacing the window but since the house is stucco with the exterior bumpouts around the window I think it becomes a real mess.

2. With limited wall access (ie. holes under crown, base and casing) and existing fiberglass insulation I assume nothing can really be done without removing existing insulation. In other words nothing could be "pumped in" effectively because of course it would just be blocked by the existing insulation.

3. If I were to remove large sections of drywall, what would my options be then?

Thanks

Windows will be only thing you can improve on. Walls are fine.