Secondary glazing used in conjunction with our acoustic Window Reveal Liners the best all round approach for noisy windows but if the costs are prohibitive or you are renting a property then the following suggestions may be helpful.
You need sound absorbing foam in combination with a heavy sound blocking layer (foam/barrier composites) to reduce traffic noise through windows.
As simple way to achieve this is to build your own removable window plug.
The plug ideally needs to seal well against the battens or frame so sealing tape is a good idea. It is also a good idea to keep the wood sheet from directly touching the frame by using more neoprene strips. The plug needs to fit as tightly as possible. You can increase performance by doubling the layers of composite.