In urban areas in many countries, noise pollution is generated by the frequent use of car and motorcycle horns. The final goal of the present study is to clarify the causes of horn use and to propose a transportation system to suppress horn use. To this end, we have investigated relationships between horn use and factors such as driver awareness, behavior, and vehicular environment. Our previous study investigated causal relationships between horn use and the vehicular environment in Taiwan, and found that horn use was more frequent when gridlock occurred at intersections. The present study analyzed details of gridlock situations at three intersections in Taipei during which vehicle horns were used. We found many cases where honking began after vehicles entered the intersection to turn left during the green-light phase. In particular, drivers often used their horns when they had to wait for more than 4 seconds for the vehicles in front of them to start moving after a green light allowed left turns. Logistic regression analysis revealed that the probability of a driver using a vehicle horn was significantly affected by the duration between the signal turning green and the vehicle in front of them starting to move.