radiated from steel. This structure provides noise reduction from 3 to 6 dB(A)
through the elastic elements supporting the rail, which prevents direct contact
between the rail foot and sleeper (Nelson 1997). However, systems that use concrete ties with spring clips may not benefit from the use of resilient fasteners,
because the spring clips already eliminate any looseness between the rail and the tie
(Nelson 1997).
Another technique is the use of rail dampers (Fig. 6.1). This structure consists of
steel components and elastomeric material that absorbs the energy of rail (springs)
vibrations (Lakušić and Ahac 2012). The damping material reduces the displacement of the vibration waves along the rail, which results in the reduction of the rail
noise. Dampers are known to be an efficient way to reduce noise emission in
railway networks (Lakušić and Ahac 2012). Studies performed at the rail track
sections with rail dampers installed showed a reduction in noise from 4 to 6 dB(A),
and vibration up to 9 dB (Benton 2006; Koller et al. 2012).
Aside from rail noise, non-audible vibrations are also generated by the trains,
transmitted via the tracks, and transferred to the soil. In surface railway lines,
sleepers with elastic supports (under-sleeper pads—USPs) (Fig. 6.1) are an alternative with moderate costs (compared to floating slab track systems and ballast
mats) that increase track quality and achieve a significant reduction in vibrations
and railway noise (Schulte-Werning et al. 2012). USPs are resilient pads attached to
the bottom surface of sleepers to provide an intermediate elastic layer between the
sleeper and the ballast. The USPs are normally made of polyurethane elastomer
with a foam structure that includes encapsulated air voids (Johansson et al. 2008).
The use of USPs causes an average reduction of vibration of 16 dB due to the
reduction of the contact between the sleeper and the ballast, which increases
elasticity of the track (Lakušic et al. 2010; Lakušić and Ahac 2012).
Commonly used to isolate the noise on railways (and roads), noise barriers
(Fig. 6.1) can be an important tool for minimizing the negative effects of sound on
wildlife, especially for species that are extremely sensitive to it. These structures
can be constructed from soil, wood, concrete, or metal (FHWA 2011; Morgan and
Peeling 2012), or can be just the dense vegetation along the rails, which can, in
some cases, form an almost perfect noise barrier (Tiwari et al. 2013; Bashir et al.
2015). Soil verges along roads and railways can reduce, on average, 3 dB more
than vertical walls of the same height. However, the construction of soil verges can
require a huge area, especially if they are very extensive and elevated. The construction of artificial walls requires less space, but they are usually limited to eight
meters in height for structural and aesthetic reasons (FHWA 2011). Vertical walls
can be applied, together with soil verges, in order to further reduce noise.
Studies by Van Renterghem and Botteldooren (2012) show that a soil verge can
reduce, on average, noise levels of 11.1 dB, and walls can reduce, on average 7.7–
8.3 dB. According to the U.S. Department of Transportation, effective noise barriers can typically reduce noise levels by 5–10 dB (FHWA 2011). Noise barriers
have been mainly used to reduce the effect of noise on colonies of nesting birds
(Bank et al. 2002). However, when applied without planning, noise barriers can
cause various negative impacts on wildlife, such as the isolation of populations
90
P.S. Lucas et al.
through the elastic elements supporting the rail, which prevents direct contact
between the rail foot and sleeper (Nelson 1997). However, systems that use concrete ties with spring clips may not benefit from the use of resilient fasteners,
because the spring clips already eliminate any looseness between the rail and the tie
(Nelson 1997).
Another technique is the use of rail dampers (Fig. 6.1). This structure consists of
steel components and elastomeric material that absorbs the energy of rail (springs)
vibrations (Lakušić and Ahac 2012). The damping material reduces the displacement of the vibration waves along the rail, which results in the reduction of the rail
noise. Dampers are known to be an efficient way to reduce noise emission in
railway networks (Lakušić and Ahac 2012). Studies performed at the rail track
sections with rail dampers installed showed a reduction in noise from 4 to 6 dB(A),
and vibration up to 9 dB (Benton 2006; Koller et al. 2012).
Aside from rail noise, non-audible vibrations are also generated by the trains,
transmitted via the tracks, and transferred to the soil. In surface railway lines,
sleepers with elastic supports (under-sleeper pads—USPs) (Fig. 6.1) are an alternative with moderate costs (compared to floating slab track systems and ballast
mats) that increase track quality and achieve a significant reduction in vibrations
and railway noise (Schulte-Werning et al. 2012). USPs are resilient pads attached to
the bottom surface of sleepers to provide an intermediate elastic layer between the
sleeper and the ballast. The USPs are normally made of polyurethane elastomer
with a foam structure that includes encapsulated air voids (Johansson et al. 2008).
The use of USPs causes an average reduction of vibration of 16 dB due to the
reduction of the contact between the sleeper and the ballast, which increases
elasticity of the track (Lakušic et al. 2010; Lakušić and Ahac 2012).
Commonly used to isolate the noise on railways (and roads), noise barriers
(Fig. 6.1) can be an important tool for minimizing the negative effects of sound on
wildlife, especially for species that are extremely sensitive to it. These structures
can be constructed from soil, wood, concrete, or metal (FHWA 2011; Morgan and
Peeling 2012), or can be just the dense vegetation along the rails, which can, in
some cases, form an almost perfect noise barrier (Tiwari et al. 2013; Bashir et al.
2015). Soil verges along roads and railways can reduce, on average, 3 dB more
than vertical walls of the same height. However, the construction of soil verges can
require a huge area, especially if they are very extensive and elevated. The construction of artificial walls requires less space, but they are usually limited to eight
meters in height for structural and aesthetic reasons (FHWA 2011). Vertical walls
can be applied, together with soil verges, in order to further reduce noise.
Studies by Van Renterghem and Botteldooren (2012) show that a soil verge can
reduce, on average, noise levels of 11.1 dB, and walls can reduce, on average 7.7–
8.3 dB. According to the U.S. Department of Transportation, effective noise barriers can typically reduce noise levels by 5–10 dB (FHWA 2011). Noise barriers
have been mainly used to reduce the effect of noise on colonies of nesting birds
(Bank et al. 2002). However, when applied without planning, noise barriers can
cause various negative impacts on wildlife, such as the isolation of populations
90
P.S. Lucas et al.