###### Abstract
Through the combined application of these programs, the maximum reduction in \(L_{\text{Aeq,10 min}}\) was estimated to be 3.9 dB. The result revealed that the prohibition of horn use was not so effective. In controlling driver horn use, it is necessary to identify the factors affecting driver horn use. Various intrinsic and extrinsic factors are assumed to influence driver horn use. Driver horn use is considered an indicator of driver aggression [35]. In Scandinavia, the use of horns is generally regarded as a manifestation of driver aggression, whereas the threshold for horn use is lower and not necessarily regarded as such in Southern Europe [36]. [PERSON] has proposed a socio-psychological model representing driver traffic behaviors [37]. In this model, a certain traffic behavior is assumed to be caused by behavioral intention, which is related to psychological factors such as personal norm and moral obligation. From these studies, driver horn use can be considered one of the traffic behaviors and is influenced by the intrinsic (psychological) factors of the driver. A study conducted in South Korea investigated the relationship between driver awareness of their horn use and the manner of its use [38]. It was suggested that drivers who do not normally use horns are reluctant to use them, and that they sound a short horn when necessary to warn other drivers of danger or for the purpose of alerting them. Furthermore, another study conducted in Japan reported that the honking patterns of horn use were related to location and traffic volume [39]. The results suggested that driver horn use is influenced by extrinsic factors (i.e., situations). Based on these findings, we assumed a similar behavioral model in which intrinsic and extrinsic factors influence behavioral intentions and induce specific traffic behaviors, including the use of a horn. To address the horn noise issue, a comprehensive understanding of the intrinsic and extrinsic factors that lead drivers to use their horns is needed. The main purposes of the present study were to find the extrinsic factors of driver horn use, such as the behavior of other drivers and the traffic environment, and to propose the countermeasure to reduce driver horn use. Although the actual road conditions and situations surrounding drivers are complicated and change continuously, the relationship between the occurrence of horn use and the traffic environment was investigated. As a case study, measurements and recordings of horn use and the current circumstances of traffic were conducted at urban intersections in Taiwan [40]. We found traffic features at intersections and relationships between the extrinsic factors, such as traffic count and traffic signals, and driver use of horns. A microscopic analysis was then conducted to examine the quantitative parameters of the traffic environment related to driver horn use [41]. As a further study, this paper analyzes the effects of vehicle horn use and the traffic environment on the acoustic environment around intersections, i.e., \(L_{\text{Aeq}}\) and \(L_{\text{Amax}}\) at the measured point at intersections. Furthermore, based on the results obtained, countermeasures to improve the acoustic environment and to reduce drivers' use of their horns will be discussed. To approach these points, important data on the vehicular environment [40; 41] are restated in this paper.