In order to reduce the fatality of traffic accident up to 50%, various tools are being developed for safer operation of vehicles on the road. Serious portion of accidents are believed to be the result of driving across the lane due to either negligence or drowsiness of the driver. As a prior step to lane keeping system (LKS) which enforces a vehicle to run within its current lane, lane departure warning system (LDWS) is developed to warn a driver before it moves over to next lane unintentionally and is being widely installed by a vehicle manufacturer or sold as an aftermarket product.

Even though LDWS is believed to prevent accident and reduce fatalities by 25% and 15% respectively, its effectiveness in performance is yet to be confirmed in many aspects.

LDWS is designed to issue a warning within the tolerance limits defined on both side of the lane boundary so that the driver would take evasive maneuver back to original lane securing a safe gap against vehicles moving in the adjacent lane. Since the driver may not perceive and respond properly due to human delay in recognition and in response, the warning may not be triggered early enough.

In this study, the vehicle lateral locations relative to warning zone envelop (earliest and latest warning zone defined in International Organization for Standardization (ISO) standard, Economic Commission for Europe (ECE) and National Highway Traffic Safety Administration (NHTSA) regulations) are compared with respect to various factors including delays, vehicle velocity, vehicle heading angle with respect to the lane.

Since LDWS is designed to be activated at the velocity over 60 km/h, vehicle velocity range for the study is set to be from 60 to 100 km/h.

The vehicle heading angle (yaw angle) is set to be up to 5 degree away from the lane (abrupt lane change) considering standard for lane change test using double lane-change test specification.

There are no solid guideline for human perception and response delay for imminent accident. Tentative delay up to 2.0 second is found from emergency braking case study for accident perception while 0.54 to 0.73 second range actuation delay is necessary.

Even though further study may follow as for the assessment for human delays in more systematic approach, preliminary study still suggests that LDWS might not be sufficient enough to issue a proper warning for drivers. Thorough knowledge of human factors to the system is needed in order to understand the limit of LDWS and to facilitate the technology like LKS.