A well-designed and constructed road allows the driver to avoid encroachments into an area with obstacles in the road environment and to return safely to the carriageway. This is possible when there is an obstacle-free zone in the road environment or, in the absence of an obstacle-free zone, when a road safety barrier is used. This paper discusses the probability of a vehicle hitting a road safety barrier, assuming five sequences of events from the time the vehicle leaves the carriageway until the damage to the barrier is registered by maintenance services. The paper also presents the influence of key factors on each of these sequences. The analyses were based on data collected from a selected section of the A1 motorway, where uncontrolled encroachments of vehicles and their consequences were observed. Knowledge of the probability of vehicle collision with a road safety barrier can be used to estimate the number of potential repairs and the length of barriers (of each type) requiring repair or replacement by maintenance services.