I am from The Netherlands, where noise barriers like these are commonly built along motorways:
Now I live in England, where such structures are almost non-existent. In The Netherlands, living 200 metre from a motorway, I experienced far less noise than I do in England, living roughly 1.5 km from a motorway.
How much noise does a motorway noise barrier typically block? I realise the answer will depend on a lot of factors, probably primarily noise barrier design and distance from motorway, and likely others. The extreme case would be to completely bury the motorway, which should reduce noise to essentially zero. Ideally, I would like to have a map like the England noiseviewer where the user can toggle on or off a basic, intermediate, or advanced noise barrier and observe how noise at particular distances gets reduced, although I expect such a map does probably not exist.