If your house is on a busy street, you can buy special windows that absorb sound, or you can insulate your existing ones, but you might also want to look outside the windows to address the problem.
The best way to reduce traffic noise is actually to break up the sound waves. Generally speaking, if a barrier blocks your view of the road, it will do a good job reducing noise transmission. You can put up a sturdy fence, or you can plant some trees (trees do tend to be prettier than fences).
Though hedges grow quickly, evergreen trees work the best for blocking noise. They are better than hardwoods, too, because they are fuller and they stay that way all year long. If they will thrive in your climate, plant a screen of evergreens as close to the roadway as possible to create a barrier that will reduce traffic noise for years to come.
Hope this helps and good luck