| 6. | Planning
indications |
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6.2.1.6 Noise barriers The appropriate geometrical arrangement of obstacles (noise barriers, walls, buildings, etc.) can effectively reduce the influence of a sound source on a receiving point. Similar to the shadow of light, an acoustic shadow is formed behind an obstacle but is reduced by sound diffraction at the edges.
A noise level reduction by a barrier can be estimated in accordance with the following equation: ∆Lz = 10 lg(3 + 0,12 · f · z) The frequency f in Hz is assumed at 500 Hz for industrial noises for example.
The diagram in figure 6/12 also allows for an estimation if heff and the distance e between sound source and receiving point (flat) are known.
Noise protection walls (as in figures 6/13a and 6/13b) are frequently used in town planning as noise protection features, especially for noise abatement at roads. Adequately shaped walls can be easily integrated into the surroundings, they can be planted and the required masses of earth arise from the anyway existing earth that is excavated during the digging of a road or a building area. The area averted from the noise source can be used e.g. for playgrounds and chutes for children, pavements, bike paths and garages. Figures 6/13c and 6/13d give examples of the application of noise protection walls. One disadvantage of noise protection walls is their relatively large space requirement, which is often not available in already developed areas. In the case of newly planned projects it is both possible and necessary to secure the space required for noise protection features in the legally binding land-use plan (§ 9 (1) 24 of the Federal Building Code) even if a road for example is only to be built
later.
Another disadvantage is the reduced efficiency of walls compared to noise barriers as the upper edge of the wall is farther away from the sound source (due to the angle of repose) and bigger heights are therefore generally necessary. The solution could be a combination of wall and barrier or steeper retaining walls, which can be
planted.
As for the overall appearance of the landscape, noise protection walls are mostly preferred to noise barriers. Individual walls and barriers can disturb the discharge of cold air near the ground (CLIMATE BOOKLET FOR URBAN DEVELOPMENT, 1990; REUTER et al., 1991). Other solutions should be found in this case (e.g. cuts or a
tunnel).
The use of both noise barriers and noise protection walls is restricted within towns or cities due to structural limits. It is up to the city planners to weigh and compensate the conflicting interests justly. Noise barriers (as in figures 6/14a and
6/14b) are an efficient noise abatement measure. Many years of experience have led to a huge number of optically appealing barrier systems, which also withstand weather
conditions.
The advantage of barriers compared to walls is their significantly lower space requirement and this is why they are often the only possible shielding measure in already developed areas. They can be better integrated into the landscape by using adequate materials and by planting them with climbers. Urban design difficulties are to be assessed similarly to those of noise protection walls
(see above).
Figures 6/14c, 6/14d,
6/14e and
6/14f give some examples of how to use noise
barriers As a barrier can be established relatively close to the noise source, the height of the barrier is mostly lower than the height of the equivalent wall.
Very positive experiences were gained with low barriers (0.7 m) immediately along the tracks of railway installations in Stuttgart (FEDERAL ENVIRONMENTAL AGENCY, 1983) as the primary sound source (tracks) is directly shielded. The sound level is reduced by more than 10 dB at a distance of 10 m
(figure 6/15). In the case of multi-track routes, of course, such barriers must be established along every
track.
Standard drawings for noise barriers outside of civil engineering works ("Richtzeichnungen für Lärmschirme außerhalb von Kunstbauten", RiZaK-88) contain schematic diagrams and indications for the planning and installation of noise barriers. The technical structuring of noise barriers is laid down in the Additional technical regulations and directives for the installation of noise barriers at roads ("Zusätzliche technische Vorschriften und Richtlinien für die Ausführung von Lärmschutzwänden an Straßen", ZTV-Lsw, 1988). This directive issued by the Federal Transport Minister specifies the requirements on the material, the stability, the persistence and the sound absorption of noise barriers. It also defines inspection procedures, allocation, approval and
warranty. What has to be considered when installing noise barriers is the sound reflection. Otherwise the barriers can cause an increase of the noise level by up to 3 dB(A) for the residents living in opposite places of immission, and this corresponds to a doubling of the traffic
volume. Figures 6/16 and
6/17 give examples of this problem. So we can see that it is important to verify in every single case whether it is necessary to install sound-absorbing barriers. sound level increases at the opposite side, sound level increases in the proximity of roads due to multiple reflections and The absorption characteristics of noise barriers and sound-absorbing wall coverings are determined according to DIN EN ISO 354. We speak of highly absorbing noise barriers if the reflected acoustic beam is by 8 dB lower than the beam hitting the barrier. A special form of noise protection features are steep walls (figures 6/18a and
6/18b), which can be located between noise barriers and noise protection walls. A steep wall is a soil prism planted with low vegetation, which prevents the propagation of the sound coming from a road. The use of artificial supporting structures allows for a significantly steeper inclination of the prism's sides than the usual slope inclination determined by the shear strength of the integrated soil (KRELL). Steep walls can be used if the average sound level is to be reduced by about 6 to 12 dB through features lining the roads, the available space is not enough for a traditional earth wall or Effective noise protection can be achieved by directing roads through cuts or troughs
(figures
6/19a, 6/19b,
6/19c and
6/19d). Raised transport routes (roads, tracks), e.g. on embankments or bridges, have the advantage that the abutments or the bridge railing along the route also function as noise barrier (figures 6/20a and
6/20b). Additional noise barriers can substantially intensify the shielding effect in a given case. Three or four-storey developments for example can be protected through a raised road in an altitude of 6 m with low noise barriers. An interesting noise protection measure for the planning are long buildings which are insensitive to noise. These are closed sound-reducing buildings whose rooms facing the road are not permanently used by people (store rooms, parking garages, staircases, pergolas, bathrooms, toilets) or are protected from noise by e.g. soundproof windows (e.g. air-conditioned workspaces). This also includes e.g. uses planned along a road or the allocation of a road to a built-up area. This means that a road passing a residential area in the North is less problematic than a road in the South as there are generally less sensitive uses on the north side of a building (kitchen, toilet, bathroom, staircase). Cut-and-cover methods like detached or semi-detached houses or groups of adjoining houses do not prevent the propagation of sound through the gaps with the result that there are no quiet zones behind the buildings. Such gaps can be partly closed by garages.
Figures 6/21a,
6/21b,
6/21c and
6/21d give examples of noise abatement through buildings. According to Krell, an enclosure is a capping body over a deep-set transport route (lying in a cut), which reduces the sound from the transport route in combination with a slope or retaining wall on at least one side of the cut. An overhead noise barrier is a long hall-like construction over a transport route, which prevents a direct propagation of the
sound. Figure 6/23 gives some examples of already realized or proposed enclosures, overhead noise barriers and tunnels. Tunnels are optimum noise abatement features as the noise from roads or tracks is completely dammed in the protected area. Furthermore tunnels protect from exhaust gases.
Problems caused by exhaust gases and noise can reoccur, however, at the tunnel portals provided that there are sensitive uses. This is why tunnels must be long enough to effectively protect an
area.
The construction of tunnels is very expensive and they require costs of operation (lighting, ventilation, cleaning). On the other hand, the space above or beside a tunnel can be additionally used at higher quality for town planning purposes - an aspect which must not be neglected considering that building plots in cities are very expensive and rare.
The following example represents a special case of a noise protection tunnel. In the context of the expansion of Kleiner Ostring to two lanes, a lightweight noise protection tunnel was built in the region of the districts Neugereut and Steinhaldenfeld with a length of about 415 m and provided with continuous openings above the roadsides for natural ventilation and lighting (figures 6/24a and
6/24b). Studies supported by the Federal Ministry of Research and Technology in 1979/80 are the basis of these concepts.
Acoustic measurements carried out by the Fraunhofer Institute for Building Physics in Stuttgart gave noise reductions at ground level of about 20 dB(A) (at a distance of 10 m to 20 m from the
tunnel). Figure 6/25 shows the isophones of the noise reduction related to a road with undisturbed sound propagation. Measurements of the concentration of exhaust gases (CO) inside the tunnel proved that the natural ventilation of this tunnelling system is
sufficient.
The natural lighting through the sound features allows for a generally very good light on the road. The installed electrical lights are only turned on rarely during the day in the annual
average.
Within the first year of operation the energy consumption was lower by about 80 % than the consumption of a conventionally equipped closed tunnel. The net building costs amount to about 10,000 euros (about 15,000 dollars) per running metre and are therefore only slightly lower than the costs for a conventional closed
tunnel.
As the operational equipment is smaller, about 800 euros (about 1,200 dollars) can be saved per running metre every year (SCHURR and BÖKELER, 1990). The sound-absorbing characteristics of vegetation are traditionally overestimated. Vegetation as a noise protection measure in town planning is practically out of question as only a strip of thick woodland with a width of at least 100 m and thick undergrowth reduces the sound level by 5 to 10 dB. Single trees or bushes offer practically no noise protection.
Table 6/2 shows the reductions of the continuous sound level at a road through homogeneous vegetation in protection zones.
Table 6/2: Noise reduction through vegetation What must not be underestimated, however, is the visual shielding effect of vegetation and the resulting positive psychological implications for the affected people (figure 6/26). So we can certainly say: What the eye does not see, the ear does not hear consciously! Orientation of the buildings, constructional noise abatement measures The orientation of the buildings as well as a flat's or house's floor plan also allow for a reduction of the noise level (figure 6/27). Rooms with a less noise-sensitive use, like kitchens, bathrooms and staircases, can look onto the road while rooms with noise-sensitive uses are situated on that side of the building which is averted from the road, like living rooms or bedrooms. The noise level on the averted side is reduced by about 15 dB in the case of closed development and by about 5 dB in the case of dispersed development. (What serves as a good example of noise reduction due to a closed development is the residential quarter "Bohnenviertel" in Stuttgart). The necessary designations can be fixed in the legally binding land-use plan for a binding determination of such a land-use allocation. Provided that all active noise abatement measures have been exploited or if they are impossible (in inner city districts or in already built-up areas), only constructional noise abatement measures beyond the standard measure at the building itself can be applied. The requirements for constructional noise abatement measures can be deduced from DIN 4109 Section 5 (Sound insulation in buildings) concerning the reduction of exterior noise. The basis for the designation of the required sound insulation of exterior building components against exterior noise are different sound level ranges, to which the existing or expected "relevant exterior noise levels" are assigned. Table 6/3 gives the requirements for the sound insulation of exterior building components, separated according to sound level ranges and room uses.
Table 6/3: Requirements for the sound insulation of exterior building components pursuant to DIN 4109 The nomogram deduced from DIN 18005 Part 1 (simplified procedure, see also section 3.1.2.1) for typical road traffic situations can be used for estimating the "relevant exterior noise level" in front of facades (figure 6/28). If necessary the following additions are to be added to the average sound levels in figure 6/28:
The levels given in the nomogram take into account an addition of 3 dB compared with sound propagation in the open land.
As the walls of houses generally possess a high sound insulation value (except for some old buildings), additional noise abatement features are usually only required at windows and roller shutter
boxes.
The quality of the soundproof windows must correspond to the existing exterior noise level and the desired indoor
level.
Details on the sound insulation of windows are given in VDI guideline 2719. This guideline also contains reference values for indoor noise levels (for incoming exterior sound), which are outlined in a simplified way in the following
table 6/4.
Table 6/4: Reference values for indoor noise levels pursuant to DIN 2719 VDI guideline 2719 distinguishes windows into sound insulation classes from 0 to 6. Class 0 (leaky windows with single glazing) has an assessed sound insulation value of < 24 dB while windows within sound insulation class 6 (double windows with separate frames, special gaskets, very big pane distances and glazing with thick glass) have a sound insulation value of > 50 dB. 
and 6/30). Since the programme was launched, more than 15,000 dwellings have been subsidized in Stuttgart with a sum of about 38 million DM (about 28 million dollars). 4.5 million DM (about 3 million dollars) have been available as subsidies every year. The programme was abandoned due to savings.
Table 6/5: Sound insulation classes for windows pursuant to DIN 2719 The city promoted measures at buildings along roads with a sound level of more than 70 dB(A) during the day or more than 65 dB(A) during the night. The corresponding roads or road sections were listed in a promotional catalogue by the city. The average subsidies totalled 40 % of the costs.
Expanded subsidies pursuant to the Fiscal Equalization Act (Finanzausgleichsgesetz, FAG) were granted for buildings along particularly noisy through roads in the context of A-roads, secondary roads, district roads and major roads for supra-local traffic, starting as from a noise exposure of 70 dB(A) (previously 75 dB(A)) in residential areas and 72 dB(A) in core areas, village areas and mixed areas. Subsidies for the installation of soundproof windows in these cases totalled up to 75 %. These funds have also been abandoned.
The promotional requirements were, besides the according noise pollution, windows within at least sound insulation class 3 and a sound level reduction to at least 40 dB(A) inside the room after the installation by an expert (this was verified randomly). Dwellings which were ready for occupancy before 1 January 1973 were subsidized. Subsidies were restricted to windows in living rooms, bedrooms and children's rooms as well as breakfast kitchens of more than 12 sqm. For further information on the current promotional programme for soundproof windows in the Filder region, please
visit: (available in German) Flyer of the promotional programme for soundproof windows in the Filder region (as a PDF
file): (available in German) |
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| Fig. 6/11: Diagram of the shielding effect for a definition of the path length difference | |
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| Fig. 6/12: Sound level reduction through an obstacle depending on the effective barrier height and the distance from the development, source: DAL | |
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| Fig. 6/13a: Noise protection wall, Stuttgart-Weilimdorf, B 295 Pfaffenäcker | |
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| Fig. 6/13b: Noise protection wall, Stuttgart-Nord, Am Kochenhof | |
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| Fig. 6/13c: SNoise protection through a noise protection wall | |
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| Fig. 6/13d: Noise protection wall integrated into a row of garages | |
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| Fig. 6/14a: Noise barrier, Stuttgart-Mitte, B 14 Cannstatter Straße | |
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| Fig. 6/14b: Noise barrier, Stuttgart-Berg, B 10/B 14 Berger Tunnel | |
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| Fig. 6/14c: Noise protection through a noise barrier (as for a nearby road) | |
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| Fig. 6/14d: Noise protection through a noise barrier (as for a distant road) | |
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| Fig. 6/14e: Alternative between noise protection wall and noise barrier | |
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| Fig. 6/14f: Comparison between noise protection wall and noise barrier | |
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| Fig. 6/15: Noise protection through low noise barrier along railway tracks, source: Federal Environment Agency, 1983; Dorsch Consult | |
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| Fig. 6/16: Reflection from buildings | |
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| Fig. 6/17: Reflection from shielding buildings | |
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| Fig. 6/18a: Example of a steep wall, Stuttgart-Degerloch, Bodelschwinghstraße, B 27 | |
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| Fig. 6/18b: Noise protection through steep wall | |
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| Fig. 6/19a: Example of a location in cuts or troughs, Stuttgart-Degerloch, Bodelschwinghstraße, B 27 | |
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| Fig. 6/19b: Noise protection at roads (railways) through location in cuts or troughs | |
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| Fig. 6/19c: Noise protection at roads (railways) through location in cuts or troughs plus additional barrier | |
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| Fig. 6/19d: Noise protection at roads (railways) through location in cuts or troughs plus additional noise protection wall | |
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| Fig. 6/20a: Example of a raised transport route (B 27), Stuttgart-Zuffenhausen, Frankenstraße | |
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| Fig. 6/20b: Noise protection at roads (railways) through a raised transport route | |
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| Fig. 6/21a: Example of a seamless building block, Stuttgart-Mitte, Charlottenstraße (Bohnenviertel quarter) | |
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| Fig. 6/21b: Aerial picture of the Bohnenviertel quarter with a seamless building block, Stuttgart-Mitte, Charlottenstraße | |
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| Fig. 6/21c: Noise protection through buildings | |
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| Fig. 6/21d: Noise protection through buildings (perimeter development) | |
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| Fig. 6/22a: Noise protection tunnel, Stuttgart-Heslach, B 14 Heslacher Tunnel | |
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| Fig. 6/22b: Noise protection tunnel, Stuttgart-Vaihingen, bypass around Vaihingen | |
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| Fig. 6/23: Cross sections of different enclosures, overhead noise barriers and tunnels, source: Krell, 1990, Manual for noise protection at roads and railways (Handbuch für Lärmschutz an Straßen und Schienenwegen) | |
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| Fig. 6/24a: Noise protection tunnel, Stuttgart-Neugereut (with an acoustic ceiling by Züblin) | |
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| Fig. 6/24b: Lightweight noise protection tunnel, Stuttgart-Neugereut (by Züblin) | |
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| Fig. 6/25: Isophones of the noise reduction at the Züblin tunnel in Stuttgart-Neugereut, source: Züblin | |
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| Fig. 6/26: Noise protection through vegetation | |
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| Fig. 6/27: Orientation of the uses within a building | |
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| Fig. 6/28: Nomogram for determining the "relevant exterior noise level" in front of facades for typical road traffic situations (additional information is given in the text), source: DIN 4109 | |
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| Fig.
6/29: Audio samples of an open, tilted and closed soundproof window |
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| Fig. 6/30: Soundproof window | |
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