The purpose of this research is to identify whether the road departure accident reduction performance of the Lane Departure Alert (LDA) system is consistent with driver acceptance. If a vehicle deviates from the lane, the LDA system warns the driver and/or automatically steers the vehicle back into the lane to help avoid an accident. However, the system cannot perform as expected if the driver feels that the system is annoying and turns it off. Therefore, the consistency between the accident reduction performance and driver acceptance of LDA was studied by investigating driving behavior based on a new form of two-dimensional analysis using the distance to the lane boundary (DTLB) and the lateral velocity of the vehicle.