The area of human factors psychology is concerned with how we can improve the interface between humans and machines to make it safer to operate cars, planes, and other machinery. Our cars must have horns that we can use to get a child's attention if they run out in front of our car. Before a dangerous intersection, bumps on the road may alert you of the impending stop sign. A warning light tells you that a car's gas tank is empty. However, these warnings are not foolproof. Psychologists have worked to improve the interface between humans and machines to make technology safer and more effective for the people using them.