About 3 weeks ago in a suburban neighborhood 25 mph zone here in SE PA there 
were 8 kids on small horses and ponies off the road proper, on the shoulder, 
when a 17yo came around a wide curve at nearly 75 mph.  It was too fast for the 
curve, and, surprise--there were the ponies.  He mowed them all down.  All the 
kids lived, with scrapes and bumps.  One went to the hospital because his head 
smashed the windshield, but because he'd worn a helmet, he survived, was 
treated for concussion, and released.  One of the kids that went high airborne 
had quite a few scrapes and bumps.  
One horse was killed almost instantly.  Another's rear legs were both broken.  
One gave its life to save the driver's by cushioning the impact of the car 
against the telephone pole that stopped it.  Its young rider was so traumatized 
by its crying that she got under the wreckage so as to sit with the pony's head 
in her lap trying to comfort it.  When he arrived, her father didn't find her 
at first and started to panic, until he followed the sound of it.  I don't know 
any more details, like how many ultimately survived.
2) helmets:  I think wearers- and non- should go see the slides of the head 
injuries at Equine Affaire (Ohio, in April), if they have the safety seminar 
again.  As well as statistics like % men & women & ages, you might learn what 
different types of injuries are common.  One almost unique to equestrians is 
the depression fracture which results when a horse kicks or steps on a person's 
head.  The piece of your skull that the hoof hits is punched into your head.  
On the x-ray it shows the usually roundish hoof-shaped bone lying against the 
brain and below the rest of the skull.  It requires careful manipulation, 
usually involving drilling some screws into that piece of bone, to get it back 
into place.  After seeing these slides, I started wearing my helmet when 
tacking up, and when I go into the pasture to fetch a horse whose buddies like 
to crowd and play rough.    
Live to ride again!   Bridget Brickson in SE PA