It is known that the collisions caused by lane departure events account for range of percentages among the countries studied. To help prevent such collisions, the Lane Departure Warning (LDW) system has started to be introduced in production vehicles, but there is little research on its benefits and limitations so far. In this paper we performed an in-depth analysis of the collisions and driver-related essential variables for the lane-departure collision scenarios and demonstrated the benefit estimation process. The benefit of the LDW system is estimated by comparing lane departure events when the vehicle has no LDW, and how they change with the addition of LDW. The event without LDW was modeled in 5 phases: (1) before departure, (2) starting of the departure, (3) departed the lane, (4) at the impact with an object, and, (5) after the impact. “An extensive analysis was conducted of traffic crash data compiled by the Institute for Traffic Accident Research and Data Analysis (ITARDA). The results of this analysis were used to create models of each phase of an LDW event. The Advanced Safety System & Traffic REaltime Evaluation Tool (ASSTREET), which is based on Monte-Carlo Simulation, was then used to simulate a variety of collision types. The results of these simulations were validated by comparing the distributions of fatality, serious injury, minor injury and no injury that they generated to crash statistics for Japan. Then, the effect of the LDW system was added to the lane departure events. The drivers' response delay to the LDW and the possible reactions were measured in a driving simulator test. The comparison between events with and without LDW clearly shows which cases could be prevented by the use of LDW and the ones that could not be avoided, thereby, providing us with important guidelines to improve the system performance.