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.