## 3 Analysis of Current Knowledge
### Studies Discussing the Impact of Advertising Devices on Road Accident Occurrence  
One of the first studies to address this topic was a study from the 1950s (USA, Michigan) in which rural area roads and their surroundings were studied. The roads were divided into equal length sections, where the occurrence of accidents, the causes of the occurrence, their distance from significant objects in the vicinity of the road and their possible influence on the occurrence of traffic accidents were analyzed in detail. As a result, it was found that the more complex the traffic situation (road crossings, number of traffic signs, significant objects in the vicinity attracting attention, density and intensity of traffic flow, speed), the more the number of accidents increases. The accident rate increases most in the area of both level and off-grade crossings, especially if there are advertising devices in the area of the intersection. In contrast, however, no direct and independent effect of advertising devices on the number of traffic accidents outside intersections has been demonstrated by data [13]. The results of this research were confirmed by another study conducted in the USA (Minnesota). The approach of the authors was the same (road segmentation and traffic accidents analysis). The final results were also very similar--advertising devices in intersections increase accident rates. However, unlike the previous study, this fact was also confirmed with regard to intersection sections [14]. Similar results were also reached by other authors who took a similar approach; however, the method of selecting the roads or parameters monitored differed [15; 16]. One of the major studies was a 1967 study. It was a comparison of accident rates before and after the installation of advertising devices. The authors chose 12 advertising devices and monitored the accident trends for 12 months before and the same number of months after their introduction into service. They also selected so-called control sections for these advertising devices, where they recorded the overall accident trends, which could prevent other global influences from being projected. However, during the actual processing, it was found that consistent and relevant data were only available for three of the selected advertising devices [17; 18; 19]. One of the other studies that did not clearly prove the negative impact of advertising devices is a study carried out in Sweden on the occasion of the commissioning of the first 12 advertising devices based on LED technology. This was a new element among advertising devices and its suitability was tested. The authors of the study followed the evolution of accident rates from 2003 to 2010, with 2009 being the key year in which all the devices were put into operation. The main negative aspect of the research was the short time interval after the start of operation of each advertising devices. For each facility, three sections were delineated--before advertising devices', 'during placement of advertising devices' and 'after advertising devices'. The first was the section from where the device could already be observed from the road, the second where the advertising device was clearly recognizable and the third behind the advertising device. The second and third s were generally chosen to be the same length. No increase in the number of accidents was found for these sections, which were at the level of the average of the selected period. Only for the first section (\"before the advertising device\") an increase in the number of traffic accidents could be found, but there is no clear evidence that this is an effect of the LED advertising device [20]. Another study that used accident data to demonstrate the effect of advertising devices on traffic safety also focused on LED advertising devices. Specifically, eight of these were located in Alabama and ten in Florida and were limited access highways with over 450 traffic accidents.