As U.S. highways swell with more traffic each year, one thing is certain for the traffic safety units of law enforcement agencies: more traffic means more crashes, and in turn more scenes to measure. According to statistics from the U.S. Department of Transportation (DOT), 43,443 road deaths occurred in 2006.
Doug Hecox, spokesman for the U.S. DOT, estimates it costs $200 billion for motorists to wait during traffic slowdowns and stoppages due to crashes. In addition to long traffic delays, crashes cause secondary incidents and increased air pollution. "Motorists way in the back of the line may not know there's an accident, or there may be a hill and they can't react in enough time," Hecox says. "We're trying to change road design to avoid this."
Pressure to re-open roads closed due to crashes and the probability that an accident with fatalities will face a jury are prompting investigators to eye the latest mapping technology more closely.
Crash scene measuring falls into three distinct categories: manual measurement methods, electronic measurement methods and photogrammetry.
While many police departments face a rise in crashes to investigate, budgets for buying the necessary equipment remains anemic. However, today there is an ample variety of crash measurement tools that can accomplish most mapping requirements and at various pricing levels.Inch by inch
The simplest, and probably the most widely used, manual measurement method for crash scenes is the conventional tape measure. In an online article entitled "Documenting the accident scene and the vehicles," Danny Horton, a Mississippi Certified Legal Investigator, states that a 300-foot tape is "great for measuring a large curve."
He explains the method by saying, "Just anchor one end at a point where the curve begins and stretch the tape in a straight line to whatever distance you need. Measure at least every 10 feet, perpendicular, to the edge of roadway. When you plot this, you will have a very accurate curvature."
Depending upon scene complexity, a tape measure may take too long or sample the scene too sparsely. More popular is the Rolatape, from Rolatape Corp. in Watseka, Illinois. The Rolatape is a wheeled measuring device with digital counter that quickly and accurately measures critical distances (in feet or meters) for crash reports. With pricing beginning at $99, these devices are lightweight, durable, easy to store, and even measure accurately on rough, uneven terrain.Total package in total stations
Most law enforcement agencies today employ a mix of electronic accident scene mapping tools or just one specific kind of mapping device. Among the chief electronic mapping methods include total stations, laser measurement systems, GPS and laser scanners.
The total station remains a desirable measurement method among trained crash reconstructionists and traffic officers because it combines electronic distance measuring (via a cooperative laser to measure distances) and a theodolite, also known as an electronic transit, for measuring angles. The total station calculates distance by sending the laser to a prism attached to a prism pole, which is held on or over physical evidence found at the crash scene. By using a simple time and velocity calculation along with horizontal and vertical angle measurements, the "points" of evidence are collected.
After researching various equipment options, the Hamilton County (Tennessee) Sheriff's Office Traffic Division found that a Topcon total station from Topcon Positioning Systems Inc., located in Livermore, California, and the Pocket Zone data collection software from The CAD Zone Inc. in Beaverton, Oregon, best suited its needs and budget.
According to Mark Kimsey, senior crash investigator with the Hamilton County Sheriff's Office, when taking measurements using a total station, the investigator places the total station at a location from which a view of all relevant evidence points can be observed and measured. Because the prism is mounted on an 8-foot telescoping pole, the total station can easily measure over the tops of stationary or moving objects, including moving traffic. Most of the time, only one placement of the total station is necessary, although it's not difficult to reposition the total station if required.
During the measuring process, one investigator points and aims the total station towards the evidence to be documented, then presses the "Enter" button on the total station's data collector. As the various points for the crash scene are shot, they are fed into the data collector. The coordinates (X,Y and Z) for the point of interest being measured have already been determined in relationship to other evidence collected, and then stored in the data collector as well.
As the various points for a crash scene are shot, they are recorded by the Pocket Zone software, which runs on a handheld computer. Pocket Zone automatically saves all of the point data and creates a scaled diagram, which is displayed on the handheld computer. By using different codes, the operator can choose to connect any points with lines, arcs or curves, and these will be displayed in Pocket Zone.
Total stations range in price from $3,000 to well over $13,000. However, "Total stations are capable of measuring angles and distances very accurately," says Kimsey. "Our traffic division has shot points extending more than a 1/2 mile, with some elevation changes measured at 200 feet, and the accuracy has been astounding."Laser measuring devices rising in the ranks
Laser measuring devices, such as those offered through Centennial, Colorado-based Laser Technology Inc. (LTI), are increasingly being used for crash scenes. The LTI laser systems combine reflectorless laser technology and electronic data collection, are easy to use and set up, and require minimal training. Complete LTI mapping systems cost between $5,000 and $9,000, which, for many police agencies, makes them more affordable than total stations or spatial measurement systems.
The Dayton (Ohio) Police Department uses five LTI Impulse 200 range/height lasers with a TDS Recon data collector, from Tripod Data Systems, located in Corvallis, Oregon, and Pocket Zone diagramming software, which Officer Jonathan Seiter, a traffic investigator, says "is a lot cheaper than buying five total stations." The department also uses LTI UltraLyte 200 Series mapping systems, which are unique since they can handle speed enforcement and accident reconstruction, making it an easier sell at budget time.
The Impulse range/height lasers, which can take measurements to non-reflective targets and obtain distances up to 1.4 miles, are lightweight, completely waterproof and can be handheld or mounted on a tripod. "One person can go out and map the scene since our department uses the LTI Impulse lasers," notes Seiter. Total stations, on the other hand, typically require two operators (except for expensive robotic total stations). LTI's Impulse 200 lasers also have a built-in inclinometer (tilt-sensor) that allows the user to measure slope-corrected distances, which is needed for 3D mapping.
Finally, LTI allows users to add its MapStar Angle Encoder to an Impulse or UltraLyte laser, which then allows full 3D mapping capability. The angle encoder will calculate a turned, horizontal angle, which is coupled with range and tilt information from the laser. This provides all required data to derive XYZ coordinates for any target.
LTI's QuickMap 3D (QM3D) accident investigation package has helped the Lake County (Illinois) Major Crash Assistance Team (MCAT) investigate crash scenes quicker and easier. The QM3D consists of an LTI Impulse distance/height laser and a MapStar Angle Encoder. A key capability of the QM3D is its field flexibility, offering three mapping techniques. It adapts to any scene, regardless of size or terrain, and the user can easily transfer all field data points and notations into a CAD drawing program.
Grayslake, Illinois, police officer Joe Manges, who serves with MCAT, recently responded to an accident scene involving a single vehicle crash on a busy, four-lane state road. The road had two curves throughout the 1,000-foot crash scene. Using LTI's MapStar Angle Encoder, Manges was able to map the scene and reopen the roadway within 2 hours after his arrival.
"We can definitely complete the scene (using an LTI Angle Encoder) a lot faster, and we know for sure it's to scale," adds Manges. "We can include 100 times more points this way than we could measuring it by hand, which took several hours. It (the angle encoder) just makes you more thorough in your job, and more accurate."GPS and laser scanning systems
GPS technology has been applied to crash scene investigations over the past few years, although it is not a widely used method. AutoDocs, from OPTIMUS Corp. in Silver Spring, Maryland, is an automated crash scene measurement and document system. Using GPS technology, AutoDocs automatically generates a graphical representation of a crash scene that is accurate to less than 2 centimeters.
According to OPTIMUS, this system makes more effective use of manpower resources since only one individual is required for operation. An investigator simply points at crash scene objects, and AutoDocs automatically records the GPS measurements for each point. Then the processing software accurately draws the scene and generates a companion text-based accident report. The report also can be wirelessly e-mailed.
OPTIMUS no longer supports its AutoDocs product, although the company is interested in selling the product licensing.
Laser scanning systems, which tend to be expensive, represent another interesting electronic crash scene measurement method. Basically, a 3D scanner is capable of capturing information from a large area of space. They typically can scan 360 degrees on the horizontal and 150 degrees on a vertical area. These scanners produce a very dense dataset of XYZ coordinates for 3D visualization and measurements. Data files can be huge, containing millions of coordinate points (a typical scan will have more than 9 million points) that are quite accurate. Many of these systems have their own viewing software, or the data can be exported to various other 3D programs.
One offering in this crash measurement category is the DeltaSphere-3000 3D scanner from 3rdTech, located in Durham, North Carolina. In operation, a rotating mirror directs a laser in an arc around the scanning head. This then rotates on a motorized base to produce a 360-degree panorama. As the scanner laser rangefinder scans the scene, in 2 to 15 minutes, it takes millions of exact measurements as well as digital photographs.
Next, SceneVision-3D software, which is bundled with the DeltaSphere-3000 scanner, allows the user to take measurements and convert the data points and photos into a high-resolution 3D depiction of the scene. Once completed, the scene can be viewed from any vantage point, and the distance between any two points can be measured.
Cost of the DeltaSphere-3000 3D scanner is $30,000 to 40,000, and can be purchased with or without color.3D measurements from photographs
Photogrammetry, the technology of obtaining 3D measurements from photographs, is gaining traction with reconstructionists and traffic investigators since it is a one-person operation and takes a short time to accomplish at a crash scene. It typically involves using a digital camera and close-range photogrammetry software.
Investigators use a digital camera on scene to take photographs from two or more perspective angles that record the 2D positions of specific feature points. The photogrammetry software then uses these photographs to determine the XYZ coordinates of these feature points via a process of photogrammetric triangulation.
Among the benefits of using photogrammetry is the image recording process is very fast, reducing time required at the crash scene. Studies have shown that police officers have, on average, reduced on-scene mapping time by 50 percent using photogrammetry, which is a great asset to officer and motorist safety. The imagery from this method also provides a permanent, irrefutable visual record of the scene. Another key benefit is the ability to measure any objects or items visible in the photos, if needed for litigation later.
Proponents of photogrammetry claim the 3D data accuracy of this method is comparable to total stations but at a fraction of the overall relative cost. For a moderately priced digital camera and close-range photogrammetry software, the price tag is about $2,000, or roughly 20 percent of the cost of a total station.
There are several software programs which use the technology of close-range photogrammetry. These programs vary in price and method used to ultimately determine the measurements needed by a reconstructionist.
The iWitness photogrammetry software program from DeChant Consulting Services in Bellevue, Washington, is the most recent entry in this crash scene mapping category. iWitness is specifically designed and optimized for accident reconstruction and forensic measurement, making it the program of choice for agencies like the Florida Highway Patrol.
"I spend far less time sweating out at the scene because I can map it significantly faster compared to other measuring methods I've used in the past," says senior traffic homicide investigator Cpl. Dave Templeton of the Florida Highway Patrol.
There are at least two other photogrammetry applications — Photomodeler from Eos Systems in Vancouver, British Columbia, Canada, and ShapeCapture from ShapeQuest Inc. located in Ontario, Canada. Alternative photogrammetric software programs like these were designed for more general photogrammetry applications, but can still be used to map a crash or crime scene.
Close-range photogrammetry has other pros and cons that are important to consider. One advantage of photogrammetry is that the processing of data is accomplished by the software after leaving the scene. This means that as long as the appropriate photographs were taken at the scene, accurate measurements can still be obtained months or even years later — long after all physical evidence has been removed from the scene. This makes a case for taking photographs of a scene that can be used later for photogrammetry, even if a total station or other measurement method is already being used. Then, if it is later determined that some important data was not obtained at the scene, investigators may be able to retrieve it from the photographs.
It's important for anyone using close-range photogrammetry at a long crash scene to be aware that special procedures are sometimes needed to link the pictures into one mapping project. A typical 6-megapixel digital camera can produce photographs with usable resolution at a range of about 200 feet. Some photogrammetry programs, such as iWitness, have a feature that "stitches" together a series of photographs taken of a long scene to produce accurate 3D measurements.Funding enhances availability
If the sticker shock for mapping equipment proves too much for the budget, there is financial help available. According to Al Baxter, administrator for the Accreditation Commission for Traffic Accident Reconstruction (ACTAR), "The first stop they should be making is their governor's officer of traffic highway safety." This state government representative should be able to process grant applications to the National Highway Traffic Safety Administration, which offers grant opportunities for technology equipment purchases and other facets of traffic safety.
The grants are helpful if a law enforcement agency wants to purchase just one total station for its officers to share, but cannot afford it.
"The next alternative would be a laser mapping device," says Baxter. "The selling point of getting a total station or a laser, as far as the grant goes, is if you can reduce traffic congestion by opening up a crash scene quicker, or you can get more accurate measurements than some other method."
Also, suggests Baxter, if a municipality is small, "You can work with your detective bureau and public works people to share equipment like a laser. You have this piece of equipment that's available for measuring crash and crime scenes, yet it's good for the public works department if they need to measure road widths or do surveying. It's a multi-sales point, not just strictly for promoting the measurement of crash scenes."
With the ever increase in traffic and accompanying crashes, mapping tools are a necessity for all departments. Considering the variety of technology and funding opportunities available, departments should be able to equip themselves for when crashes need to be investigated. It's time to get smart about crash scene mapping technology.
Bob Galvin is a freelance writer in Oregon City, Oregon, who writes on topics relating to crash scene reconstruction technology. Galvin can be reached at firstname.lastname@example.org.