MUNDANE MYSTERIES: Why “Objects In Mirror Are Closer Than They Appear”

Anyone who’s ever driven a car has seen the little warning on basically every passenger-side mirror: “Objects in mirror are closer than they appear.” But, why can’t objects be displayed accurately in those mirrors?

It’s actually a careful design choice made with safety in mind.

The way we see things depends on how light reflects off the objects around us. An object’s shape, color, texture, other characteristics, all factor into the direction & intensity of the light which bounces off of them. If the objects are reflected off an intermediate object, like a mirror, then the way we perceive the original object could be distorted.

Our perception is also affected by the shape of the mirror. Here in America, passenger-side mirrors are convex, or curved slightly outward, while driver-side mirrors are flat. A convex mirror placed on the passenger side reduces the driver’s blind spots on that side of the vehicle by presenting a wider field of view. But, it also makes other cars appear farther away due to the slight distortion caused by the shape. The flatter mirror on the driver’s side gives you a more accurate depiction of what’s behind your car using a more narrow field of view, since light is bouncing off in the same direction that it’s hitting the mirror, so that it doesn’t distort the reflection of the object.

When the reflections of the two mirrors are combined into the driver’s point of view, you have the ability to see wider areas of the passenger side of the vehicle while also being able to keep your eyes mostly on the road. That flat-convex combo has been the U.S. standard for years. However, the Department of Transportation’s looking into the safety benefits of two convex mirrors, which are what most European cars usually have.

For now, though, you should always remember to check your mirrors frequently, and always look over your shoulder before you change lanes. Oh, and please, please, please…don’t forget to use your turn signal!

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