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.
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.