Great article.
 
You're right, that 92% figure (people who signal) sounds 
way to high.  Because signalling lets people know what 
you're doing, signalling is in fact an act of common 
courtesy.  From what I've experienced, I don't think 92% 
of Americans -- or North American for that matter -- have 
enough common courtesy to signal.
 
Other usability/safety features I would like to see on vehicles:
 
Blindspot-free rear view mirrors:  Checking your blindspot is 
actually dangerous, since you're looking over your shoulder 
and really taking your eyes off the road.  Making the rear view 
mirror a little wider and a little more convex can help.  I'm 
not sure why car manufacturers are so skimpy on this feature.
 
Brakes lights in the front:  Brake lights should also be in the 
front of the car for the same reason that turn signals are also 
in the front of the car:  It tells people what you're doing.  
Seeing brake lights in the front allows me to react faster than 
waiting to figure out whether or not the guy towards me is 
intending to slow down or stop.  Reading the brake lights are 
as useful as reading turn signals when I'm about to engage a 
heavy intersection.
 
Pressure-sensitive brake lights:  I would like to see brake 
lights that are sensitive to how hard the person is pressing 
on the brakes, telling me whether they're intending to slow down 
or to stop immediately.  This could be very useful on larger 
vehicles, as they tend to cover a large portion of your field 
of view.  For usability reasons, the lights should be in a series.  
One light would indicate light brakes, whereas all lights would 
indicate heavy brakes.  Combied with the brake lights in front 
idea, this could also give law enforcement an edge over speeding.