Motion Settings

Very frustrated. If I set my motion settings to pick up movement around my vehicles I also pickup every car going past. If I set it low enough to miss the cars I don’t pickup around the vehicles. If I set it strong enough to pick people up it also gets the cars. I have the cameras pointed down as far as possible, the motion zones are set way back. I walk into it and the camera does not trigger on me but does pick the car up 30 yards away. Any suggestions???