The least expensive option is going to be to create white noise.
Otherwise, you'll need some type of sound insulation and dense pack cellulose might be able to be retrofitted into the wall cavity. But ... read more
Remember also that the window will need to be tempered glass, if you try to DIY this project. While you should consult with a local remodeler (find a chapter of NARI near you, or a Builders Associatio ... read more