Soundproofing existing double glazed windows

So we have a new build which is 3 years old and has new double glazed windows with trickel vents.

We get a bit of noise from the main road which is about 20m away, but there is about to be 1500 houses built on the other side of it and we think we need to increase the soundproofing on that side of the house. Considered secondary glazing, but I just wondered if anyone had any other ideas? I’d really not rather rip out a practuclaly new double glazed window and replace it, unless anyone knows of any good solutions?
Thanks…

As usual, I need to answer with some questions.

Is there adequate ventilation without the trickle vents at the front of the house,

How deep are the window reveals from inside wall to glass?

Perhaps more surprisingly, what type of floor and flooring do you have?

Here is something for you to ponder regarding sound waves. You will see that the sound will travel between buildings and defract around corners, so you may need to soundproof more than just the front of your house.

https://www.docbrown.info/ephysics/wavesound-2.htm