Time- to- line crossing (TLC) is defined as the remaining time that a vehicle travels from the current po-sition to the lane boundary.It has been used as a trigger warning criterion for lane departure warning system,sothat its calculation accuracy plays a key role.In this paper,the trajectories of vehicles driven on straight andcurved road sections are investigated on the basis of vehicle kinematics and trigonometric function,and the estima-tion models of the TLC respectively in straight and curved vehicle paths are then presented.Finally,the effects ofvehicle lateral distance,relative yaw angle and road curve radius on TLC are analyzed in a simulative way.The re-sults show that (1) in straight paths,TLC is inversely proportional to the relative yaw angle but is proportional tothe transverse distance; (2) in curved paths,TLC is inversely proportional to both the relative yaw angle and thepath curve radius but is proportional to the transverse distance; and (3) the above- mentioned relationships are op-posite to those when the vehicle runs across a lane border in an opposite direction.This research effectively reducesthe false alarm rate for lane departure warning systems using TLC as the decision criterion.