One of my favorite examples of Human Factors Engineering is the Center High-Mounted stop Lamps. We have all seen them on every personal vehicle manufactured today. They are now a safety requirement. But it was not always that way. So, what is a CHMSL? CHMSL are red stop lamps mounted on the center line of the rear of a vehicle, generally higher than the stop lamps on the sides of that vehicle. They are activated when the driver steps on the brake pedal and off at other times. A CHMSL is necessary on vehicles less than 80″ wide with a gross vehicle weight rating of 10,000 lbs. or less. The CHMSL must be on the vehicle’s rear center line, at least 34″ from the ground. In addition, the lamp must be red.