We all know the raised reflector buttons on the lane divider lines of a freeway. They have white or yellow retroreflectors embedded in their edges, so that at night they shine right back at you in the light of your car’s headlamps. Safety and beauty in the same simple device.

But what many may not realize is that they have another design feature, also safety related, and far more ingenious. At least in some freeways – California’s, for sure – the buttons’ other edge – the one facing away from oncoming traffic – has red reflectors in it. Why put reflectors on the side you never shine a light on, the side you can’t even see?

Precisely because of the one circumstance when one would be seeing it: when they drive on the freeway in the wrong direction, having entered via the off ramp instead of the on ramp by some colossal mistake – think DUI, for instance. Now you have a drunken driver going in the wrong direction at night; traffic is sparse, but any moment disaster may strike unless this fool notices his mistake. And now those reflectors return the investment – for this driver will see long lines of red lights shining ahead to infinity; so unusual as to immediately alert him that something is wrong.

And if, like me, you never did that, you can still see the effect if you drive facing straight into the sun when it is low in the sky; you can then see the red reflectors, shining back the in the sunlight, in your rear view mirror!