According to the National Highway Traffic Safety Administration (NHTSA), a statistical projection of traffic fatalities in 2011 shows that an estimated 32,310 people died in motor vehicle traffic crashes. Put in perspective, this is good news: Traffic fatalities have been steadily declining over the last five years since reaching a peak in 2005. These statistics are encouraging. But the truth is, accidents, fatal and otherwise, continue to pile up and investigators see no letup in the steady flow of crash scenes to document.
Crash scene investigations present multiple challenges: the need to quickly re-open partially or fully closed roads at a crash scene; keeping the scene and its evidence undisturbed as first responders enter it; and the substantial length and scope of some crash scenes, requiring lengthy data plotting. Moreover, investigators, who must often work close to moving traffic at a scene, must be kept safe (for more on the importance of reflective duty gear, check out "Time for Reflection"). Motorists, who can become anxious after long waits and distracted by crash scenes, must be prevented from causing secondary accidents.
This is intensive, specialized work. As police budgets have been slashed, the latest crash mapping tools have allowed agencies to do more with less. Reconstructionists must therefore be trained and skilled at scene mapping technology to get the job done well and quickly.
In the Palm of Your Hand
Michael Allard and George Maglaras are trained crash reconstructionists who have been field-testing the latest laser crash scene mapping system from Laser Technology, Inc. The Tru-Speed Sx—a rugged, handheld device that combines speed detection and the ability to measure horizontal distance, vertical distance and slope angle for crash and crime scene mapping—is their latest project.
The TruSpeed Sx comprises similar features and accuracies found in the widely used LTI Impulse 200 laser rangefinder for crash scene measuring and UltraLyte 200 LR speed measuring laser system. For scene measuring, it can instantly switch between reflector and reflectorless mode, and it will work with radial angle, range triangulation and baseline offset mapping techniques.
The TruSpeed Sx’s 7x sighting scope is easy to articulate, allowing quick location of a reflector. This magnification makes it easy to view a long-distance shot. Weighing less than a pound and fitting easily into the palm of your hand, the TruSpeed Sx deploys effortlessly. And, notes Allard, operating the TruSpeed Sx is enhanced by the “limited number of buttons on it.”
Allard particularly values the Sx’s ability to smoothly change between reflectorless and reflector modes, which is controlled by one button. “It’s quick,” Allard says. “There are internal and external filters that fit over the lens,” he says. “The external filter, for example, allows you to discriminate even more to look for the most reflective target.”
Maglaras, owner of Computer Collision Investigations in Southern California and a traffic patrol officer with a Southern California police department, estimates that using LTI’s new laser mapping system will allow most of his crash scenes to be mapped within three hours.
“This measurement system is quicker than manual methods, especially when you have a curved roadway and you must take a lot of measurements,” Maglaras said. “That’s where the Sx excels, because it accurately documents the curvature of the roadway.” Using the LTI mapping package “automatically calculates where to put those points in the XY coordinate system, and when you connect those points, you then get the curve of the roadway.”
A key feature of the Sx is its 2,000-foot range. Most scenes are mapped at a distance of 600 feet or less, but the 2,000-foot range works for extended scenes. Investigators can position themselves farther away and move equipment less. “I’ve yet to find a scene that’s been too large (to map),” Maglaras says. “And, the Sx has the same laser diode in it as the LR 200.”
Finally, the TruSpeed Sx’s light and compact design makes it ideal for Maglaras to break down with his other LTI equipment after mapping a scene and it’s easy to carry—a key advantage given how much equipment officers must bring with them to crash scenes.
The total station for years has been a widely used instrument for crash scene investigations. It takes fast, high-precision ground measurements.
Total stations come as reflectorless, robotic and with GPS applications capability. Reflectorless mode allows for measurements to objects or points without having to place a prism at those points. Robotic mode allows measuring from a distance via remote control, eliminating need for a second operator to hold a prism pole. For GPS applications a total station can be equipped with a GPS receiver on its prism pole. The receiver uses the transmission from a GPS base station, which establishes a known 3D coordinate point.
According to Sgt. Mark Kimsey, with the Traffic Homicide Division of Hamilton County (Tenn.) Sheriff’s Office, there’s increased mapping and diagramming of crashes because the public is demanding more intensive crash investigations. Sgt. Kimsey, with another sergeant and two crash investigators, mapped 100 crashes in 2011, 18 of which involved fatalities. The two Topcon total stations he and his team use each work in reflector and reflectorless modes.
For medium-size crash scenes, “We set up the total station close to the debris field and shoot a lot of the small pieces of debris reflectorless,” which would involve an area 400–600 feet, Sgt. Kimsey explains. “But when we get into distances, we want to use the prism for accuracy. We’ve shot scenes up to 2,600 feet long using our total station and a prism, and, in another case, a scene 191 feet vertically involving a car going off a bluff.”
Long Scenes in Open Areas
Las Vegas is a hotbed for crashes, particularly fatal ones. Already, the percentage of fatalities has risen nearly 76% this year over 2011, according to William Redfairn, lead detective in the Las Vegas Metro Police Department’s (LVMPD) Fatal Crash Investigation Detail.
The Detail investigates between 200 and 300 fatal crashes out of more than 30,000 traffic accidents annually. To document the fatal crash scenes, the LVMPD frequently uses two robotic total stations (Sokkia SRX series) and three Sokkia GRXI GNSS systems from among a large arsenal of mapping equipment. The LVMPD’s wide variety of total stations is essential due to the volume of crashes to be processed, a desire to keep abreast of technology, and so that detectives can map crash scenes independently whenever possible.
Total stations using GPS are ideal for Las Vegas, with its wide open desert terrain and clear skies, which allow satellite signals to be reliably captured. The receivers automatically generate any correction signals. “The two main benefits of using GPS total stations are quick, easy functionality and one-person operation,” Redfairn says. “These devices increase our detectives’ efficiency with investigating crash scenes, and the accuracy is second to none.” Perhaps the only downside to using GPS-assisted total station is that it can’t function effectively in the absence of satellite signals due to heavy cloud cover or dense vegetation and trees.
In addition to general crash scene documentation, the LVMPD also uses its total stations to map crush occurring in accident-damaged vehicles. “When you’re animating a crash scene, you can show the crush of the vehicle so much more accurately,” Redfairn says.
Redfairn views the scaled diagram created with total stations using GPS receivers as particularly useful for numerous forensic purposes: “Now you have data that you can use in animation, scene reconstruction and simulation.”
Photos & Data Points
Photogrammetry is another effective crash-scene documenting tool that is growing in popularity. With it, 3D measurements can be extrapolated from 2D digital camera images acquired from various angles at the scene. These images are fed into special software, which processes the data points captured and produces a 3D model. The 3D photogrammetry modeled points and lines are then converted into a 3D diagram using a computer-aided drawing program.
‘Point Cloud’ Models
Laser scanning for documenting crash scenes is attracting many law enforcement agencies. Although the cost of a laser scanner typically exceeds $100,000, it’s a compelling tool. With it, a laser is emitted from the scanner at thousands of times per second. The laser beam is bounced off the scanned area or object to fixate on the precise location of an X, Y and Z coordinate system. Millions of points are collected by a camera sensor built into the laser scanner. These points create a “point cloud” that’s then converted to a 2D or 3D model.
Investigator Troy Snelgrove of the Palm Beach County, Fla., Sheriff’s Department decided to use both a total station and laser scanner to map the crash scene for the recently closed case involving a Bentley slamming into a Hyundai and pushing it into a filled canal two years ago. The Bentley’s driver was convicted of DWI manslaughter and vehicular homicide as a result.
Snelgrove needed to prove there were no visual obstructions for the vehicles’ drivers as they were about to collide. He used a Sokkia 530R3 reflectorless total station to map the crash scene for an eventual 2D diagram. The MapScenes Evidence Recorder software was used to record total station points, along with MapScenes Forensic CAD/Capture to draw 2D and 3D diagrams and create animated 2D diagrams of the roadway and evidence.
Shortly after the diagrams were created, Snelgrove’s department acquired a laser scanner, which Snelgrove concluded would be ideal for texture mapping of the point cloud created for the crash scene and then building an animation. Using the total station and laser scanner would verify collected evidence points. Yet, he wondered, how could he validate the scanner’s representation of evidence?
Snelgrove decided that by overlaying the 2D diagrams of the scanned crash scene, he could provide the verification. “I wanted to be able to say, ‘here’s the animation as the car drives through, and the 2D drawings over the animation and point cloud to show that it’s dead on.’ I’m verifying that my point cloud is right based on my total station drawing. It’s my interpretation, but [the diagrams and point cloud] are doing exactly what I’m explaining [they’re] doing.”
In recent years, crash investigators have been using a somewhat newer approach to reconstructing scenes: satellite imaging, specifically, Google Earth and Microsoft Bing Maps. Used in conjunction with total stations and diagramming software, spatial imaging has been very effective.
Master Patrol Officer Joe Warren with the Chattanooga, Tenn., Police Department uses aerial imaging with a Topcon GPT 3207 NW total station. Crash evidence points plotted with the total station are fed into The Pocket Zone data collection software from The Crash Zone, Inc. Next, the 2D or 3D diagram created by Pocket Zone is overlaid onto the crash scene’s aerial view.
“This verifies what we measured on the ground with our total station—skid marks, length of skid marks, where tire marks ended and where the vehicles ended up,” Warren says.
Frequently, he and his investigators can map evidence on one side of a roadway, but since the road must be kept partially open, gathering evidence on the other side of the road is difficult or impossible: “The aerial photos of the scene allow us to fill in the rest of the diagram for the portion of the roadway or intersection we could not get using a total station.”
When It’s Time for Diagram, 3D Popular Choice
When it’s time to create a diagram based on plotted crash scene evidence points, some reconstructionists and traffic investigators prefer 2D. Others feel 3D is the only way to go.
The 3D representation is widely used because it helps juries best understand the sequence of events in a crash, as well as where key evidence is located. Specialized diagramming programs such as MapScenes Evidence Recorder/Forensic CAD, The CAD Zone, Inc,’s Pocket Zone (for on-scene data collection and quick diagramming) and The Crash Zone desktop drawing software, and FX 3 from Visual Statement, are software that collect data from total stations or laser devices. The data collected, in the form of points, arcs, curves, notes and so on, are then imported into diagramming programs.
These software programs also enable users to attach digital evidence to the diagram file, including photos, video and audio files. This allows you to substantiate your diagram against photo evidence.
Another advantage is that most crash diagramming programs today offer layering of various crash scene aspects. Reconstructionists in particular favor this capability. It saves valuable time and gives a variety of separate, individual scene perspectives.
One of the biggest achievements in crash scene diagramming software is the ability to show 2D or 3D motion of any symbols in a diagram. The user draws the path of the symbols he wishes to put in motion (vehicles, commercial trucks/trailers, bullets, people, etc.) based on measurements captured at the crash scene. Then, after adding variances of velocity and rotation, the whole scene can be animated.
Do animations really give an accurate representation of scene events as they most likely occurred? Many reconstructionsists feel they do, but agree that any animation must be accompanied by other data and evidence.
Rande Repp, an officer and reconstructionist with the Salina, Kan., Police Department, values animation. “The ability to have an expert witness giving testimony and showing animation and graphics and computer visuals would seem to carry a lot more weight with the jury than expert witness testimony alone,” he says. The animation isn’t ironclad, “but based upon the evidence, the testimony, the totality of circumstances, this is the best that we can reproduce as accurately as possible.”
Whatever crash measuring equipment you purchase, you must train on it. Although training is another cost, it’s well worth it. Once you’re officers are in the field, facing those dangers, they must be assured of the equipment’s full range of capabilities. Grants funding is available not only to acquire crash measuring systems, but to train on them too.
Joel Salinas, an officer with the Vallejo, Calif., Police Department and expert reconstructionist, thinks about training on another level: “Are [the agencies who are buying mapping systems] getting the right training?”
It’s not enough to simply go to a surveying equipment supply store, get some basic training on system setup and then begin mapping scenes. Officers must learn all of the equipment’s capabilities, how to diagram mapped scenes, then actually practice measuring sample scenes with the equipment under professional supervision.
Bottom line: To effectively document crash scenes, investigators and reconstructionists must always think about how a mapped scene will be received in court, and use whatever current technology is affordable to plot evidence and make presentations as compelling, accurate and as indisputable as possible.