# Possibilities of Evaluating the Effectiveness of Noise Barriers in Slovakia
## 4 Discussion  
In this study, we used several methods to evaluate the effectiveness of noise barriers used in real conditions in Slovakia intended for noise reduction in the vicinity of newly constructed motorways. The methods specified by standard ISO 10847 [28] are proposed for determining the insertion loss of noise barriers for acoustic shielding of various types of noise sources. The standard specifies detailed procedures for measuring the insertion loss of barriers at their locations (in situ), including definitions of the microphone positions, source conditions, and the acoustic environment of the measurement sites. It allows measurement of the insertion loss of a barrier at a given location and for given meteorological conditions. However, it does not allow comparison of the values of the insertion loss of the equivalent barrier measured at different locations. It can be used to compare the values of the insertion loss of different types of noise barriers at the same location and under given meteorological conditions using a direct measurement method. This standard specifies a method for determining the insertion loss from the level difference before the installation of a barrier (without barrier) and after its installation (with barrier). If this is not possible because the barrier has already been installed, then the indirect method should be used to estimate the sound pressure levels prior to the installation of the barrier by measurement at another location that is considered as equivalent. For an equivalent location, a close match of the characteristics of the source, the positions of the microphone, the characteristics of the Earth's surface, and the terrain profiles, in the surrounding man-made structures and in the meteorological conditions is required. The standard prescribes principles to ensure sufficient equivalent conditions that allow some reliability and repeatability of determining the value of the insertion loss of the barrier between the situation before and after the installation of the barrier. This standard does not cover the determination of acoustic quantities of a barrier in an indoor environment, such as the airborne sound insulation index and the sound absorption coefficient. We used this method to measure the insertion loss of the selected barrier at the end of the bridge structure on the newly built section of the D1 motorway. A regulated artificial sound source was used as the noise source, thus fulfilling the condition of close matching of the characteristics of the noise source. The resulting value of the insertion loss of the barrier obtained from the measured values was 19.1 dB(A). At the same time, simulation of sound propagation from a source was performed using our own calculation program based on the methodology according to Commission Directive (EU) 2015/996 [31,32]. From the simulation, a value of 19.6 dB(A) was obtained, which testifies to the quality construction and fabrication of the assessed barrier. Further measurements were performed according to standard EN 1793-6 (Adrienne method) [29], which is used to qualify the products being installed along roads as well as to verify the compliance of the installed noise reduction of barriers with their design specifications. This method can be used to qualify a barrier for noise reduction for other applications, such as barriers along railway lines or industrial zones. Regular application of the method can be used to verify the long-term properties of a barrier. The method uses the same principles and devices to measure sound reflection (given by standard EN 1793-5 [27]) and airborne sound insulation (given by this standard). This test method should not be used to determine the intrinsic airborne sound insulation characteristics of barriers that are installed in reverberant conditions, e.g., inside tunnels or deep cuts or in galleries. This standard introduces a specific quantity called the sound insulation index to define the airborne sound insulation of a barrier.