Dan Simmons - Darwin's Blade

“The details are pretty boring,” said Dar.

“Details don’t bore me, Dr. Minor,” said the chief investigator coolly. “They’re the core of my job, too, remember.”

Dar nodded. “OK, first I’ll run through the data and equations and then show you the forensic animation that results from them,” he said. “I prefer metric units in this sort of work, though I usually translate to English units of measurement for demonstrations.”

Dar typed and the street scene appeared again without a van, with only the two men emerging from the apartment building and one of them stepping into the street. The viewpoint swooped down again as if the viewer were looking from a van turning west onto Marlboro Avenue from Fountain Boulevard. The figure far down the street was clearly visible.

“Nighttime visibility studies show that even on a dark country road, even with the van’s dim lights on, the pedestrian—in dark clothing—would be visible for about one hundred seventy-five feet, even if the driver had poor to mediocre eyesight. It’s one hundred and sixty-nine feet from the Fountain Boulevard intersection to the point of impact with Mr. Kodiak.”

“She saw him as soon as she came around the corner,” mused Syd.

“Had to,” said Dar. “Whether he was still on the curb or had stepped out. Her high beams would have picked him out at more than three hundred forty-three feet away. Hell, if she’d had no headlights on at all, she could have seen him from one hundred fifty feet away because of the streetlights and spill light from the apartment building main lobby.”

“But she accelerated,” said Syd.

“She sure did,” said Dar. “The front tires of the van left skid marks for a total distance of one hundred thirty-two feet. That is, she kept skidding for twenty-nine feet beyond the point of impact where Mr. Kodiak left his right shoe and scuff marks from his left shoe.”

“She says she ran over him at that point,” said Syd.

“Impossible,” said Dar. “Once we have the skid marks, everything becomes a matter of simple ballistics. Velocities and distances traveled—for the van, the man, and the body—can be figured easily. Shall we skip the equations?”

“No,” said Syd. “I meant it when I said that I liked details.”

Dar sighed. “All right. Both the LAPD Accident Investigations Unit and I conducted separate skid tests on this street with vehicles equipped with bumper guns—”

“Pavement spotters,” said Syd.

“Right. The test vehicles’ speeds were determined by radar. The test skids yielded a consistent value for a drag factor, f, to be 0.79. From that we can find the initial velocity of the pedestrian at the contact point…Remember, all testimony says that Mr. Kodiak was struck while standing still and facing the van. His velocity can never be greater than the van’s. So we use this equation—

The values are simple. The van skidded to a full stop, so its velocity can be given as ve = 0. The value for acceleration, a , is given by a = fg. As I explained, we determined the drag factor, f = 0.79. The figure for g , the pull of gravity, = 32.2 feet per second in U.S. measurement.”

“Or 9.81 meters per second per second,” Syd said quietly.

Dar blinked at her. “ You think in metric equivalents,” he said. “Shall I skip the rest of these equations and go to the animation? You’re probably ahead of me.”

Syd shook her head. “Details. Show me.”

“OK,” said Dar. “Because the van was decelerating, a has to be a negative number. Gennie’s van skidded a total of one hundred thirty-two feet. Therefore, we just substitute back into the equation for initial velocity—

The van’s velocity when there are twenty-nine feet left to skid can be done in the same way. The only value that changes is the value for distance, d. So that equation would read—

That was the van’s speed at impact. And that would become Mr. Kodiak’s speed as he became airborne at impact. This equation works with tall-fronted vans, by the way, but won’t work with most smaller cars.”

Syd nodded. “The vertical grille of a truck or tall van produces a flat-on impact, near the pedestrian’s center of mass,” she said. “A regular sedan or a smaller car would hit below that center of mass and throw the victim onto the hood or over the roof of the car.”

“Yep,” said Dar. “Or cut him in half.” He looked back at the equations on the screen. “So because Ms. Gennie was driving this rental van and got Dickie front on with the grille, the math is simple. We just have to know the typical values for pedestrian drag factors over various surfaces.”

He tapped a key. The screen read—

SURFACE RANGE

Grass .45–.70

Asphalt .45–.60

Concrete .40–.65

“And Marlboro Avenue?” said Syd.

“Asphalt.” Dar typed in the pedestrian drag factor, f, as 0.45.

“The value for this particular pedestrian’s center of mass height, h, was—2.2 feet,” said Dar. “And the measured distance between the initial contact point of impact—confirmed by the shoe he left behind and the scuff marks from the other shoe—to his final position as determined by blood and body scuff marks was seventy-two feet. So we substitute those values into the above equation—

“So the velocity at the beginning of Mr. Kodiak’s fall—that is, his separation from the braking van—calculates out as—

Which is consistent with the earlier skid analysis,” said Dar.

“So she actually hit him doing about twenty-seven miles per hour, braking from a top speed of almost fifty-six miles per hour,” said Syd.

“Fifty-five point seven,” agreed Dar.

“And he flew backwards seventy-two feet from the point of impact, coming to rest on his back with his head farthest from the van,” continued the chief investigator.

“As ninety-nine-plus percent of pedestrians hit straight on by such a van would,” said Dar. “That’s why Larry and I knew that foul play was involved as soon as we saw the officer’s photographs.” He tapped at keys until the equations disappeared from the screen and the original animated street scene returned. Another tap got rid of all the numerical values of lighting, curb height, skid length, and so forth.

Two male figures stepped out of the building. The van screeched around the corner from Fountain Boulevard and began accelerating madly down Marlboro Avenue. One of the men pushed the other man, who stumbled into the street, almost fell, and then righted himself just as the skidding van slammed into him. The body flew a long distance, landed on its back, and skidded farther, finally coming to a stop. The van pulled away and accelerated around the corner of the next intersection, cutting off a Ford Taurus that stopped. A man got out, knelt by the victim, and then ran west, disappearing around the corner to go to his friend’s apartment to call 911.

“We found blood, hair, and brain matter on the right wheel, the hub of the right wheel, the front transaxle, the shocks, and on part of the catalytic converter of the van,” said Dar tonelessly.