The main danger (which the Manual, to give it proper credit, does warn motorists about) is that a vehicle visible in the extra small mirror is MUCH closer than it appears. If the driver cannot also see the car in the main mirror, then the logical conclusion is that the car is already in the notorious blind spot. The incident occurred in twilight, before many drivers had turned on lights but when cars could be harder to see. The driver’s brain, in low light, might confuse the two mirror images and believe the car to be at a safe distance when it is already trying to pass, a “human error” that is more likely than it sounds. (Fortunately there was plenty of shoulder yesterday where this happened. But a passing driver could be thrown into a ditch or into a barrier, with the driver causing such an accident unaware of what he or she has just done. )
The Focus does offer the Blind Spot Information System, described on p. 167. Mine does not have this, and I have never rented or driven a car with one. It could probably be installed by a dealer for several hundred dollars.
Again, the Manual warns that the Information System is not a substitute for actually looking. Dependence on the dual mirror is not a substitute for the shoulder glance maneuver. Again, cars in other lanes without lights in twilight can be hard to see, even by a driver operating properly. Leaving the power window down a bit can help, making hearing the vehicle more likely.
In early 2012, an older Focus was struck by a car to my right on a local street when I was in its blind spot, resulting om $3000 damage (although it looked cosmetic).
The blind spot to one’s left can be as tricky as the better known blind spot to the right.
In older eastern cities and suburbs, many intersections need protected left turns. In Arlington County VA, for example, a protected turn is badly needed from Geroge Mason northbound onto 16th St., or from Glebe Road northbound onto 16th St. Many intersections still need “No Right Turn on Red” because of poor sight distance, requiring drivers (under pressure from motorists behind) to creep forward to look, risking pedestrians and wrong-way cyclists.
There is controversy in San Francisco over whether cyclists should be required to come to a complete stop at every stop sign, link here. This would not be a big deal in itself, but cyclists should be required to ride with traffic (not against) and honor stop lights. One problem with cyclists running lights is that a motorist has to pass the same cyclist multiple times safely (which is not a problem if there is a separate bike lane). Wrong-way cyclists are likely to be missed by motorists turning onto a street, expecting traffic from only a legal direction. FindLaw has a primer on all this here. The biggest liability risk for the average motorist is probably still striking a cyclist or pedestrian in a hard-to-see environment.
Update: Oct. 30
Last night, as I approached the Breezewood exit on the Pennsylvania Turnpike from the west, at night, I was confronted with the sudden loss of the right lane when the road work signs warned only of loss of shoulder. Since there was a concrete birm on the left, this could obviously cuase the deceived driver to make a sudden maneuver, forcing someone behind him or her into the birm, a catastrophic accident. Maybe Pennsylvania law gives the lead car the right-of-way, but I was shocked at such a dangerous situation was allowed. ,
Update: Nov. 9
Cyclists: At night, if you barrel down a hill in rain, with glare from street lights, and have only a small head light and dark clothes, drivers just might not see you, even when you have the right of way. Watch your speed around any intersection.
Update: Jan. 28, 2017
Here's an LTE to the Washington Post where a cyclist says growups need not to become cowards and be willing to ride in full traffic (LTS4).