In general, human drivers inevitably experience a time delay when they recognize the danger they encounter, make a judgment, and take action. This time delay is called cognitive reaction time, and is an important figure in response to emergency traffic event, such as collision avoidance. Cognitive reaction time has been studied by researchers in various fields, and it is estimated to be about 0.75 seconds based on measurements of responses to stimuli or driving experiments. However, these cognitive reaction times are experimental values for the case of psychological readiness, and it is inappropriate to apply directly to actual cases in the real traffic situations. In this study, more than 300 commercial vehicles in daily operation were equipped with commercially available drive recorders to measure the cognitive reaction time under actual traffic conditions. The data obtained from more than 1000 cases showed that the 95% confidence interval of the population mean included a cognitive reaction time of 0.75 seconds to 0.8 seconds, which is reasonable for psychologically unprepared human drivers in an actual traffic environment.