The Society of Automotive Engineers recommends adjusting the side mirrors on your car so that there’s no overlap between what you see in the interior (“rear view”) mirror and in the wing mirrors.

I made this adjustment a couple months ago and I love it. For me, the goal isn’t to avoid ever looking over my shoulder. That seems unnecessarily lazy and still potentially dangerous. What I avoid is the need to check repeatedly.

When looking for a safe opportunity to change lanes, I may know there’s a car passing me but not know how far it’s come or whether there’s still enough room behind it for me to merge there. I’d end up checking over my shoulder several times (taking my eyes off the road for many seconds in total) before maneuvering. With this simple adjustment to the mirrors I can watch the traffic develop through my peripheral vision and only check over my shoulder as a final precaution when I’m actually ready to move my car.