I find adjusting them properly is all that is needed. It takes some getting used to, but it works.

Most people have their side mirrors adjusted so they can see the side of their car, and they cover pretty much the same area as the rear view mirror. Wrong!

To adjust the left (driver side) mirror - Place your head on the window - adjust the mirror out until you can just barely see the side of car.

On the right (passenger) side - sit as you normally would, but lean your head far to the right - adjust the mirror so you can barely see the side of the car.

When done correctly, you can watch a car approach in your rear view mirror - just as it is passing out of site in that mirror, it will become visible in your side mirror - as it passes out of that mirror, it will be next to you and visible in your peripheral vision.