In many countries' urban areas, noise pollution is produced by frequent use of car and motorcycle horns. It is necessary to clarify the reasons for horn use and propose measures to control it. To investigate the relationships among horn use and such factors as driver awareness, behavior, and vehicle environment, we conducted a questionnaire survey in Taipei, Taiwan. Respondents were asked about their normal horn use, their understanding of the law about such use, their impressions of horn sounds, and their personal attributes. The questionnaire covered the following: intrinsic factors (e.g. attitudes, personal norms); frequency of horn use (i.e. behavioral intention); and judgement about horn use under certain traffic conditions. Our results should lack of awareness about legal horn use. Regarding the relationship between intrinsic factors and behavioral intention for horn use, such factors as attitude, perceived behavioral control, and moral obligation were related to the strength of the behavioral intention to use the horn. Concerning extrinsic factors, logistic regression analysis revealed that speed differences with the vehicle ahead and another car cutting in ahead affected horn use.