ᐅ Noise protection

Hello everyone,

I’m new here!
I just registered and would ask you to please be patient with me.
I hope my topic fits here.
This is my first forum!

My name is Chris, and I am from southern Germany.

My garden is located below a busy country road.
My sloped property is separated from the road by an old stone wall.
The wall is about 1 meter (3 feet) high and 50 cm (20 inches) thick, a typical old rubble stone wall.
The wall runs along the entire length of the property and has an arched opening every 10 meters (33 feet), measuring 115 cm by 60 cm (45 inches by 24 inches) through which the traffic noise is clearly audible in the garden.
Trees or hedges are not possible because the garden and the road surface have a height difference of about 4–6 meters (13–20 feet) with a steep slope.
By the time plants would grow that tall, only electric cars might be around. I don’t want to wait that long.
What could I do to cover or close the openings in the wall to reduce the road noise?
In summer, especially motorcycles accelerating on the scenic winding mountain road can be heard loudly, which I understand.
That’s why I’m asking for your advice.

Thanks in advance for your answers.

Best regards,
Chris