Acoustic barriers which are positioned along traffic lanes are designed to protect the surroundings from excessive noise. Such structures are to reverberate, diffract and damp the propagating acoustic waves. However, this method of shielding has some disadvantages which include constraint visibility and structure-born noise. The interaction between traffic-caused movement of air mass and acoustic barriers may generate infra noise waves. That is undesirable and should be estimated. The authors undertook the research to diagnose the plausible side effect of structure-born noise of such barriers because it may influence human body (Kasprzak, 2014). As a mechanical structure, the acoustic barrier is characterized by mechanical parameters which, in the field of modal analysis, are made up of natural frequencies, damping factors and mode shapes. In this paper the authors investigated the acoustic pressure distribution in the neighborhood of a real acoustic barrier in the scope of infra noise propagation. The methods of modal analysis were used to identify natural frequencies of the barrier and dominating frequencies of propagating waves in the far field. The correlation between observed vibration and acoustic signals is presented.

The author analyzes the relationship between the size of GDP generated in the region and its metropolitan capital city, and the level of budget revenues of local government units – including the metropolis. On the example of Małopolska and Cracow, it observes tendencies of the growing level of income of local governments in relation to GDP, but fi rst of all it points out that in the metropolitan city the ratio is much lower than in the whole region. This defi ciency is called the „metropolitan income gap” and looks for the reasons for its occurrence. He points to the dynamic suburbanization, which causes that more and more groups of people contributing to the production of GDP in a metropolitan city pay property taxes, personal income and a large part of VAT in the suburban area. What is more, the areas of this zone use various forms of development support – for example, development of rural areas. The author considers the phenomenon of the «metropolitan income gap» to be a negative phenomenon, limiting the ability to compete on a global scale and points to several possible ways leading to its reduction. The author considers the phenomenon of the «metropolitan income gap» to be a negative phenomenon, limiting the ability to compete on a global scale and points to several possible ways leading to its.