Best way to help reduce street noise

[Lacey Denton]

I recently purchased a great duplex, but it is on a busy street. The street noise drives me crazy! All of the other units are rented out, so obviously it is not a deal breaker for everyone, but are there any tips on how to reduce heavy street traffic noise? I have researched sound-proof windows, but they are very expensive. Anyone else have any inexpensive, DIY tricks? Thanks!