The Rearward View with Mirrors
When do we rely our mirrors the most? Probably when we are changing lanes. Our objective is to change position without getting in another driver's way or cutting him/her off.
The positioning for the inside rearview mirror is fairly obvious -- you should be able to see out of the rear window. Be sure the day/night switch found on most rearview mirrors is in the day position during daytime operation
As for the sideview mirror or mirrors, most people adjust them so they can see the side of the car on the inside edge of the mirror. Consider the view when the sideview mirrors are set up as just described. Essentially, you have created "tunnel vision" to the rear. Your sideview mirrors overlap much of what your inside rearview mirrors sees and you've also created blind spots.
What in the solution to tunnel vision and blind spots? Simply adjust the sideview mirrors just beyond the point where you could see the side of the car on the inside edge of the mirror. With this setup, you almost completely solve the blind spot problem.
For the case where there is a vehicle present that isn't visible when checking the mirrors, the vehicle's position will probably be such that its front is adjacent to your door and you'll spot it in your peripheral vision as you check the sideview mirror.
Most of us have dealt with blind spots by turning our head for a quick check. This isn't generally a problem in terms of missing something ahead; however, there can be a dangerous side effect. Unless you've worked to control it, your arms will move in the direction your eyes are looking causing the steering wheel to turn. With well-positioned mirrors, your head won't have to turn as far to check any remaining blind spots.
There are other applications of changing lanes that this setup is useful for as well. For example, when getting on a highway, your ability to judge how to best merge with the traffic flow will be greatly enhanced with the view provided by the "wideview" side mirror.
Likewise, as you pass interchanges on the highway, your ability to monitor traffic entering the highway is enhanced.
And finally, a good guideline for deciding when to move into the passing lane or back into the traveling lane is to make sure that you can see the headlights of the vehicle you want to pull in front of in the rearview mirror. We can all appreciate the value of adequate pull-in space.
Source: "NMA Motorist's Guide to State and Provincial Traffic Laws", pg 6-8; 1994, National Motorists Association (6678 Pertzborn Road, Dane, Wisconsin 53529; 608/849-6000; firstname.lastname@example.org).