I certainly agree that lingering in the vicinity of big trucks longer
than necessary is indeed a bad idea from many standpoints.  However,
it is irrelevant to this accident, in which the loose wheel bounced
over the center divide like a demented robotic deer and bashed
somebody in the midst of multiple lanes of oncoming traffic.

As I understand it, this is pretty typical ofttruck-wheel-separation
accidents -- those things have a lot of momentum and, being round and
rubber and fast moving,  take crazy bounces (amid a general trend of
moving forward and outboard, which makes sense considering the
momentum vector they have when they come off).   The only real way to
guard against it is in truck maintenance -- not only care to torque
the lug nuts (doublechecked by the driver) but inspection for fatigue
cracks, etc., and proper lubrication, adjustment, and inspection of
bearings.

I don't have recent statistics, but the problem came up for a lot of
scrutiny in the early 90s when in a span of a few months it caused
five separate fatality accidents (three in one state), and at that
time it was estimated that there were 750-1000 such failures annually
in the US.  (http://www.ntsb.gov/publictn/1992/SIR9204.htm)

Once they *do* come off,  the only chance you have is to not be in the
wrong place at the wrong time, and perhaps hope to see it coming and
hit the hole.[1]  That tire/wheel combination can weigh upward of 200
pounds and if that truck was moving fast, so is the wheel, a speed
that you can add to your own...

--Joe

Teaching oneself how to seek refuge under the dashboard without losing
control is a useful skill in various rare but plausible situations,
like the time either a flying ostrich or a reincarnated pterodactyl
escaped from some secret genetic engineering lab and hit my
windshield.   Actually it was one of the really big owls -- wingspan
about enough to fill the windshield of one of those big old Jeep
Wagoneers.  It swooped down into my headlights to get some owl
delicacy off the freeway, and  my higher mental functions had just
enough time to think, "Owl," when the lizard part of my brain decided
it would be a good idea to inspect the transmission hump at close
range.    I cautiously raised back up and discovered a ruined but
intact windshield and a rather graphic tableau of what's inside an
owl.  I just happened to have some clear packaging tape and a pair of
safety glasses in my toolbox, so I  fortified it and drove home
cautiously at the minimum order of 45 mph.  The next day the insurance
lady expressed considerable skepticism over the phone.  I offered to
stop by so the remaining smears of small-animal carnage could be
inspected in person.  At that point she realized that a glass shop
near me had a direct-billing program with my insurance company and
they really wouldn't have to deal with it in person after all.

And that was at least an order of magnitude lighter, not to mention
softer and slower moving, than a lost wheel from a truck coming the
other way...  It's bigger than you are and coming fast from an
unexpected angle and (plus or minus the state trooper advice quoted in
that article) quite often there probably isn't much that even a fairly
alert driver can hope to do in terms of evasive action.