This paper presents a study on the implications for road safety of the use of passing beams during the day. The genesis of the problem and conditions that have led to the use of passing beams by vehicles during the day is presented first. Then, the photometric requirements for passing beams are evaluated in terms of their signal role, comparing them with the requirements for daytime running lights. The main part of this paper presents a report on field tests carried out under real road conditions. The tests were done in order to measure the impact of using passing beams by day on the distance at which the oncoming vehicle could be detected. Also, the correctness of the estimation of relative positions of oncoming vehicles at the same or different distances was examined with different combinations of passing beams on or off in the tested vehicles. The research confirms the effectiveness of using passing beams during the day and the need to harmonize the obligation to use passing beams.