Soundproofing against street noise - what can be done?

I can't imagine that it can be made really quiet. Maybe a bit quieter - but the houses opposite reflect the sound anyway... I would probably put bushes on the border and then something again directly in front of the terrace...

Ok, thanks for the info. Are there certain bushes/shrubs you have in mind?

no, I'm not even sure yet what I want to achieve with us, although we need less than you. But since I tend to be more "eco" there, it should definitely be something native, and mixed, so not just one type, and not strictly in a row to go along with the hedge trimmer.
for example
- Schlehdorn
- Roter Hartriegel
- Kornelkirsche
- Hasel
- Eberesche, Vogelbeere
- Schwarzer Holunder
- Berberitze
- Wildrosen
- Alpenjohannisbeere
- Feldahorn
..... whatever grows well in your soil.

3 meter stone wall

- Blackthorn
- Red Dogwood
- Cornelian Cherry
- Hazel
- Rowan, Mountain Ash
- Black Elderberry
- Barberry
- Wild Roses
- Alpine Currant
- Field Maple

I will pass this on to the landscape gardener! Thank you!

We once had to calm down a whirlpool in the old town center (mixed-use area) so that the neighbors wouldn’t go crazy. It was just barely under the allowed decibel level. We were dealing almost exclusively with the low frequencies. I believe traffic noise on cobblestones has rather lower than higher frequencies. You have to use something heavy and dense. It must not be able to vibrate like, for example, a lighter metal structure. Sound stops at obstacles. It doesn’t climb up or anything like that. It would have to originate at the ground level with a tire/cobblestone noise. Anywhere you can potentially even just peek through, the sound will come through as well. Concrete or thick natural stone blocks should help. Best regards Gabriele