Each driver should drive according to the actual road traffic rules of the country in which is he currently located. The law systems of various states of Europe allow an increased maximal blood alcohol level of driver. As the fact that no small number of road accidents is caused because of the influence of alcohol on the driver, it is necessary to focus the attention of the society on this issue. The paper deals with the influence of alcohol to change of the reaction time of the driver. During the project of the alcohol effect on the driver and its behaviour, the reaction time of several drivers of a selected group of people was measured. At first (before alcohol drinking) it was assessed the physical and mental condition of the drivers, using a series of question. Subsequently were carried out the measurements by car with sober driver. After this initial measurement the driver began to drink an alcohol and after 20 minutes the level of alcohol in driver´s breath was determined by certificated equipment. After finding of this value was the driver re-tested by the car, where he had to stop the vehicle before simulated barrier. During the tests the stopping distance, the mean fully developed deceleration was explored as the supporting variables. As the most important variable was the driver´s reaction time. It was researched by using of the video-analysing from two synchronized cameras. The aim of this paper is to focus on the fact that there is a dependence between the amount of consumed alcohol and the driver´s reaction time, which significantly affects the road safety. The reaction time of the driver directly influences to the stopping distance thus it is resolute for stopping the vehicle before a barrier