US Patent 7532981 Vehicle departure detecting device

Lane width information Winf acquired by a traffic lane detector is retrieved (step S1); when a value of the lane width information Winf is within a predetermined range of change amount relative to a lane width output Wout_old at a previous time step, i.e., not less than (Wout_old+Wdec) nor more than (Wout_old+Winc), Winf is used directly as the lane width output Wout (steps S5→S9→S11→S8); when the value of lane width information Winf is off the predetermined range, i.e., less than (Wout_old+Wdec), (Wout_old+Wdec) is outputted as the lane width output value Wout (steps S5→S9→S10→S8); when the value of lane width information Winf exceeds (Wout_old+Winc), (Wout_old+Winc) is outputted as the lane width output Wout (steps S5→S6→S8).