You can replace the windows on the street side with triple panes instead of double panes. I've heard that helps reduce outside noise and have heard if people doing that who live under National's flight path. And make sure installation is as tight as possible.

We live on an avenue with local neighborhood traffic only. It's not a huge noisy problem at all, but for our child's comfort level since her room faces the street, we want her to feel totally cocooned and hear virtually nothing. Any recommendations? Thanks!