Question:
I would suspect that you would see the total miles rode per year go up fairly steadily, while the fatalities declined 15% from 1993 to 2000.

If there was just a 10% increase in total miles, then added to the 15% decline in fatalities would give about a 25% relative decline in fatalities per miles rode. That isn't bad.

BUT... this data gives no info on WHY the decline. Better safety education? Better brakes? Safer road conditions? More aluminum frames (just being facetious)? Fewer cars on the road?! More recumbants? Fewer children riding? Brighter colors? Who the heck knows!?

This graph says virtually nothing about helmet effectiveness. All I know is that helmets saved the lives of a couple of my buddies when we rode motorcycles (helmets destroyed on impact but heads not harmed at all). And if I were to get slammed into a telephone pole I would rather be wearing a helmet than not. Obviously helmets can't protect from all injury, but they can certainly reduce head injuries in many situations. (At about 5% or less of the bicycle and gear cost, and a few ounces, that is not a burdensome price)

Answer: If I had a choice, I certainly wouldn't wear one if it it made me uncomfortably hot. I've looked at many sets of data before huge increases in helmet wearing when laws were introduced and I really don't believe there's any evidence to suggest helmets work well enough to make it worth wearing them, if it's at all inconvenient.

There's even a theory that, though helmets prevent minor wounds to the head, they may even increase the risk of brain injury because they increase the size and mass of the head which may increase the turning forces on the head, leading to rotational injury. (Most brain injuries are what is known as DAI (diffuse axonal injury) caused by roatations of the head, not direct blows.)

The National SAFE KIDS Campaign and Founding Sponsor Johnson & Johnson are teaming up to send a simple message to parents and kids when on any kind of wheels – Use Your Head. Wear a Helmet!

“Brain injury is the leading killer and disabler of children,” says Dr. C. Everett Koop, Sc.D., former U.S. Surgeon General and chairman of the National SAFE KIDS Campaign. “Damage to the brain from an external blow can affect one’s ability to walk, talk and think. The consequences can be devastating and permanent and change a child’s life – suddenly and forever.”

While more than three-quarters of tweens surveyed said that a brain injury could occur as a result of a wheel-related crash and 65 percent of kids knew that the effects of a brain injury could last a lifetime, less than half said they wear a helmet on every bike ride. Less than a third wore a helmet while riding scooters, skateboards or inline skates. Only 9 percent said that it is likely they will suffer a brain injury while riding.