Privacy and noise protection on a slope through poplar caps or fir trees?

We are building on a medium-sized road. In the photo taken from the northwest, I have marked the embankment leading from the property down to the road in red:

In the site plan (oriented to the north), the various trees can be seen (they are all poplars) as well as the slope with elevation meters marked:

Unfortunately, the growth is not as dense as it appears in the photo, especially in autumn and winter it is rather bare there, and you can easily see through. Accordingly, the noise from the road is quite high.

Our idea was now to prune or break the poplars at about 4-5m height and lay them sideways, so that they continue to sprout and over time we obtain a natural "hedge." To reinforce this, we considered planting fir trees at the bottom of the slope, as these also protect well against views and noise and look good in winter. These should also be pruned after a maximum (!) of 4-5m above our property, partly to keep maintenance manageable, and partly not to overly block the western sun.

Is this at all feasible, or is there a better solution?

A retaining wall is unfortunately too expensive.

hmm so you can cut back poplars as long as enough green remains at the top so that the tree continues to grow upward and does not form extreme root suckers.
To my knowledge, firs/spruces are not suitable for being regularly cut at the top – firstly, the shape no longer looks nice, and secondly, they probably become unstable due to the unnatural growth form/weight distribution.

I would first shape the poplars and see how they grow and where there are gaps. Then consider with a gardener or preferably an arborist what might make sense to add.

Nice that the poplars would work out!

I have already read about the unwanted side effects of topping fir trees, but somehow hoped that regular pruning at this relatively low height could counteract them. A neighbor has a similar "fir hedge" at about 3-4 meters high, which he regularly trims, hence the idea.

Something evergreen would be nice, so that you don’t have to rely only on the poplars. Maybe cherry laurel?

With cherry laurel, you're totally wrong with me, I hate that stuff
How about holly?

or rather I have to revise that - the locations don't agree. Poplars like it moist, holly less so... I'll keep thinking about it

Plant growth provides zero point zero sound insulation. If you need sound insulation, it must be incorporated into the building design.

Plant growth provides zero point zero sound insulation. If you need sound insulation, it must be incorporated into the building planning.

Damn, that's true. I quickly googled:

Planting

The sound insulation effect of plantings is often greatly overestimated by laypeople. As an urban planning measure for noise protection, planting is hardly considered, since only a 100 m wide dense forest strip with dense undergrowth results in a level reduction of 5 to 10 dB. Individual non-densely planted

trees or shrubs provide virtually no sound insulation.

Reductions in the continuous noise level at a street through homogeneous plantings in protected zones are shown in Table 7/2.

Planting
additional noise reduction
through planting

Forest without undergrowth0.05 dB(A)/m
Forest (average)0.10 dB(A)/m
Dense deciduous forest0.15 dB(A)/m
Coniferous forest stands0.20 - 0.30 dB(A)/m
Very dense hedges0.20 - 0.30 dB(A)/m
Tab. 7/2: Noise reduction through planting

However, the visual screening provided by planting and the resulting positive psychological effect on those affected should not be underestimated. Figure 7/27:.


In this respect: What one does not see, one does not consciously hear! Trees along the roadside can also serve as a design element to enhance the streetscape and reduce the nuisance effect of noise for residents and pedestrians.

Annoying!
Would it perhaps be more sensible in this case to pile up the slope somewhat and thus achieve a "noise protection wall," or to build a small wall at the upper end?
The street is already 1.5 to 3 meters lower than the property. So something along the lines of:


Sound insulation will be installed on the building anyway, but we are mainly concerned about the garden, which begins behind the trees.