Lane change detection

The present invention relates to a vehicle safety system comprising a detection system (2), an emergency control unit (14) and safety means (15, 16). The detection system (2) is arranged to detect a target vehicle (8) positioned longitudinally and laterally displaced relative the detection system (2), and to define a target vehicle rectangle (22) that at least partly encloses the target vehicle (8), constitutes an approximation of the target vehicle (8). The target vehicle rectangle (22) comprises a boundary (k) positioned along a second bearing (13) having a second azimuth angle (´' 1 + ´' 2 ) with reference to a first reference line (6). The target vehicle rectangle (22) comprises a first corner (j) that is closest to the detection system (2) and is positioned along a first bearing (12) having a first azimuth angle (´' 1 ) with reference to the first reference line (6). The detection system (2) is arranged to calculate a yaw movement (¸ A ) of the target vehicle (8) by means of the first and second azimuth angles (´' 1 , ´' 1 + ´' 2 ). The present invention also relates to a corresponding method.