We live about 100metres away from a dual carriageway. The noise was disturbing, especially at night when it is used as a launch pad, for high powered motor bikes hoping to break the land speed record.
We already have a new UPVC window, so what I have done is fit blocks of Celotex very snugly between the roof joists in the area above the noisy room. The effect on noise was instant, it also made the room a lot warmer in the winter, even without the heating on.
My wife made roman blinds with a blackout lining to fit inside the window reveal ... and we then fitted new heavy curtains also with a blackout lining. For the curtains I fitted a new track, so they hung very close to the wall. We dont see street lights shining round the side of the curtains at night, in fact we dont see anything at all and are no longer bothered by the noise from the road.