## Traffic Science

NPR this morning had a program on speeding. One of the "experts" they brought in was Richard Retting, senior transportation engineer with the IIHS (that's the Insurance Institute for Highway Safety, a group funded by auto insurance companies).Early on they asked him why speeding was bad. He said there were three reasons. The first two were straightforward: when you're going faster, you (1) travel farther before you can react to something, and (2) take longer to stop. No problem there, and I waited for the third reason, presuming it was going to be kinetic energy.

Well, almost.
The third reason, he said, was energy. "Remember that equation
E = mc^{2} from high school?"

Wow! If I drive faster than the speed limit, I'm converting my mass
into energy?
For those who haven't studied physics recently, he was probably
confusing Einstein's equation relating energy, mass and the speed of
light with Newton's formula for kinetic energy,
KE = mv^{2}/2. The host responded incredulously
"The speed of light?" but Retting didn't seem to notice, and pressed
on: "When you're going faster, your energy is disproportionate and
exponential."

Okay, you're talking on the radio and you have a brain-o.
I'm sure we've all said silly things when we knew better, like
reciting the wrong equation then not noticing the gaffe.
But he also
seems confused about what "exponential" means, perhaps because of that
"exponent" of 2 in the equation. An exponential
curve is when you
have something like 2^{X}, not X^{2}. Admittedly, the
dictionary of "exponential" includes vague definitions like
"Pertaining to exponents", and I suppose there is an exponent
of 2 involved. But really, folks: kinetic energy
increases as the square of speed.

A little later in the program, someone called in to mention studies showing that higher speeds don't necessarily correlate with accidents, and Redding chastised him for doing google searches for studies: "That's not how we do science in this country." Hey, Mr. Retting -- it might pay to be a little more careful with your own science if you're going to be dismiss callers with remarks like that.

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*18:37 Jun 07, 2007 More science | permalink to this entry | comments*]