Install thick, well-fitted curtains or soundproof drapes
Add window inserts or interior secondary glazing
Seal gaps around the window frame with acoustic caulk
Apply weatherstripping to sash and frame edges
Replace single-pane glass with double- or triple-pane windows
Use laminated acoustic glass
Install exterior storm windows
Add removable acrylic or polycarbonate panels
Use window film designed for noise reduction
Fill frame gaps and cracks with low-expansion foam where appropriate
Upgrade to tighter-fitting window locks and latches
Add heavy blinds or cellular shades
Cover vents or openings near the window if they transmit noise
Use mass-loaded vinyl panels over the window when needed
Combine multiple methods for better results