Authors: Dan Simmons
“You do three-D accident reconstruction videos,” said Syd. “I didn't see the CAD monitors in your loft.”
“They're there,” said Dar. “Tucked away in a corner behind some bookcases. Preparing these provides a big share of my income.”
Syd nodded.
“So, Chief Investigator,” said Dar, “do you see some irregularities in this accident?”
Syd looked at the dossier, at the photograph on the screen, and then at the 3-D image that showed essentially the same picture as the photograph. “Something's wrong here.”
“Correct,” said Dar. “First I investigated the lighting under similar conditions with a specialized light meter.”
“At two-forty-five
A.M.
on a cloudy, rainy night,” said Syd.
Dar raised his eyebrows. “Of course.” He tapped some keys.
Suddenly numbers appeared on the 3-D image of the street scene. Dar moved the mouse and rotated their viewpoint until they were looking straight down at the street, east to west, with the van near the bottom of the screen, the body centered, and the rest of the block visible. Areas on both sides had small rectangles of data listed as FC.
“Foot-candles of light,” said Syd.
Dar nodded. “Despite Donnie and Gennie's claims, it was fairly well lighted for such a poor neighborhood. You can see that at both intersections, there are large pools of light covering most of the street at three foot-candles. The lighting at the front steps of the building puts out about one and a half foot-candles, and even in the middle of the street beyond where Dickie was hit, the lowest reading was one foot-candle.”
“She should have seen the victim even if the van's lights weren't working,” said Syd.
Dar touched the screen with a stylus and a red line appeared, running most of the way back to the intersection with Fountain Boulevard from whence the van had come. “Gennie came around through rather bright lightingâthree foot-candlesâand moved through this long area of two foot-candles of light until just before the impact. The van headlights were both intact and working. In fact, she had the brights on.”
Dar tapped keys and the visual on the screen disappeared, to be replaced by a real-time animation. Two men, three-dimensional but featureless, emerged from the front door of the apartment building. Suddenly the viewpoint switched to an aerial shot. The van accelerated around the corner from Fountain Boulevard and continued to accelerate. One of the figures stepped out into the street and faced the oncoming van. The van slammed on its brakes and slid most of the distance from the intersection to the impact siteâfinally hitting the man head-on and continuing to skid for another thirty feet or so. The featureless victimâDickieâflew through the air and landed on his back in the roadway, head away from the van.
Dar tapped keys and the earlier aerial animated view was superimposed over this one. “This is the actual position of the van and body at the scene.” Suddenly the van was at least forty feet back up the street to the east and the body had also moved eastâat least twenty feet from its actual point of rest, its head now pivoted around toward the van.
“Quite a discrepancy,” said Syd.
“It gets better,” said Dar. He pulled a six-page typed statement out of the dossier and let Syd glance over it. “Officer Berry, number 3501, took this statement from the first witness to drive down the streetâ¦a Mr. James William Riback.”
Syd's eyes flicked back and forth down the pages. “Riback says that he saw a van pull away from the scene, almost cut him off, and then he saw DickieâMr. Kodiakâlying on his back in the street. Riback stopped his Taurus, got out, and asked Richard Kodiak if he was alive. He reports that Kodiak said, âYes, go call an ambulance.' Ribeck left his car in the street and ran to a friend's apartment around the cornerâ3535 Gramercy Streetâawoke his friend, told her to call 911, grabbed a blanket, and rushed back to the sceneâ¦where he found Mr. Kodiak lying in what Ribeck thought was a different location, certainly turned in a different direction, in much worse shape and unconscious. The paramedics arrived seven minutes later and Kodiak was pronounced dead. The van was parked where it is in the police photos.” Syd looked up at Dar. “The bitch drove around the block and ran over Dickie Kodiak again, didn't she? But how do you prove it?”
“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 pedestrianâin dark clothingâwould 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 traveledâfor the van, the man, and the bodyâcan 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 gunsâ”
“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 pointâ¦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 equationâ
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,” 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 velocityâ
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 readâ
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 readâ
SURFACE | RANGE |
Grass | .45â.70 |
Asphalt | .45â.60 |
Concrete | .40â.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,
wasâ2.2 feet,” said Dar. “And the measured distance between the initial contact point of impactâconfirmed by the shoe he left behind and the scuff marks from the other shoeâto his final position as determined by blood and body scuff marks was seventy-two feet. So we substitute those values into the above equationâ
“So the velocity at the beginning of Mr. Kodiak's fallâthat is, his separation from the braking vanâcalculates out asâ