At approximately 3am Sunday morning a 40-year-old Hispanic female was traveling north on Harrisburg in Houston at a high rate of speed in a Nissan Rouge. As she crossed over the ship channel at Wharf Street they believe she may have been forced off the road in the curve. She struck a guardrail ripping out guardrail anchors in the concrete. She crossed the southbound lanes and struck the bridge pillar for the railroad overpass. She died at the scene. Houston Police Officers were already taxed as they were having to work another fatal crash the happened at almost the same type. At that scene the entire freeway had to be closed. With new technology, the investigators cut the initial investigation time down by more than half.

Many years ago, a fatal accident was a crash, someone is dead and there was very little else to do but take about 50 photos, draw a rough sketch of the scene and call the local funeral home to pick the victim up and tow the vehicle off. All sometimes done within an hour. As time progressed so did technology. Investigators were able to use computers to determine the length of skid marks to determine speed. Every year there was a new advancement. Investigators started using measuring tapes to measure the complete scene. This took several investigators, one to write, one to hold one end of the tape and one to hold the other end. They also had to deal with the wind blowing the tape, the measurement being read or written wrong. Another investigator would take photos, as another would get witness statements and still another travel to the hospital if there was someone injured to attempt to obtain information. Still several others were needed to direct traffic. This took several police officers off the streets at any given time. Many depended on wreckers to block roads as there were not enough officers to go around. A fatal crash scene could take 6 or more hours of just scene investigation. The investigator would then have to go back to the office, type a report and take all the measurements they had done and make a scale drawing.

Years still progressed and several vehicle manufacturers started putting a device like a “Black Box” just like aircraft have but not near as much information. A computer could be connected to the box and data downloaded to show the final; moments of the crash. It was very limited information. They were called Event Data Recorders.

An Event Data Recorder (EDR) is a function or device installed in a motor vehicle to record technical vehicle and occupant information for a very brief period of time before, during and after a crash solely for the purpose of monitoring and assessing vehicle safety system performance.

After a module’s primary functions are complete and where appropriate thresholds are met, data may be recorded as part of the “Event Data Recorder” (EDR) functionality or capability. An “EDR” is not a standalone device and the data may not always be recorded. In some situations, there may be nothing to “image” from a module in a vehicle.


EDRs may record:

  • information, but only after some physical event like a crash
  • vehicle dynamics information and system status for about 5 seconds before a crash
  • certain driver inputs for about 5 seconds before a crash
  • vehicle crash severity signature
  • restraint use and deployment related information
  • post-crash data such as the activation of an automatic collision notification (ACN) system

EDRs do NOT record:

  • the name of the driver
  • audio or video of the crash
  • names or the identity of passenger(s)
  • the places the car has been driven
  • and the systems don’t record information unless there’s been a physical occurrence like a crash


This device helps investigators after the crash but they still have the scene investigation to do. For years’ survey crews used a transit to complete their survey work. Soon this came into play for accident investigation and reconstruction. A total work station is an electronic, optical instrument used in surveying and can be used to reconstruct accident or crime scenes with computer technology. Though the departments have been using total stations for several years now, few people realize the effect that the new technology has had on investigations and how it has changed crime scene reconstruction. Crash investigation time and the time traffic must be diverted and other officers off the street has been cut down to 4 to 5 hours.

It is a theodolite, an instrument used to measure vertical and horizontal angles, mounted on a tripod, similar to a tripod-mounted camera. It also includes an infrared electronic distance meter to measure distances from the mounted station to a rod-mounted prism placed over an object. Any data from the device is stored electronically, and in the case of the crash investigators, used to later reconstruct crime scenes and traffic accidents.

In Montgomery County DPS has one and Conroe Police Department has one. Harris County Sheriff’s Office Accident Investigation Unit has the device and Houston has used one for years. Accident reconstruction with a total station follows a process. Two officers must operate the device. The total station is mounted on a tripod at one part of the scene with one investigator operating it. Another investigator takes the rod-mounted prism, and walks the scene placing the prism over evidence that needs to be measured. This includes victims, different points on the vehicle, vehicle parts, the roadway, all the road striping, any driveways, gouges in the road created by the crash and any skid makes. Some scenes require hundreds of points to be plotted. At times on larger scenes and where additional officers are available it is possible to have two or three prisms where as one officer moves to the next plot point, another can be at another point also. The investigator then can line up the total station’s lens with the prism and measure distance, horizontal and vertical angles simultaneously. The evidence is then labeled and stored electronically.

When the field measurements are completed, the measurements are loaded into a computer program that investigators use to reconstruct the scene. The software that is used, a CAD program, can differentiate between different cars, houses and evidence and can also be programmed to move the cars at specific speeds to reconstruct the accident. The program can also show a scene in three dimensions. The devices cost between $7,000 and $36,000.

Houston Police Department last year updated the equipment with another device that works on the same principal but instead of needing several officers to operate the unit, it takes just one. One the investigator calibrates the unit he has the same pole and prism along with a small handheld computer to enter the data points in. As he moves point to point, the transit on the tripod, using radio frequency follows him, like a robot. This device allows one investigator to photograph the scene, another to conduct interviews and one to plot the crash site. The time using this device in some cases has cut investigation time to close to 1 hour. That is only 1 hour officers are off patrol duties to work traffic control, only 1 hour that motorists are stuck in traffic or having to take another route.

Every year technology changes and newer and better devices hit the market. That is also evident on where several departments across the country auction off older technology for the newer.

One such device, the Topcon/Sokkia MS-05 Total Station is now listed on eBay by a department for just $33,000 and is labeled as a demonstration unit. Once again though is the cost for many departments. Funds were made available years ago through the Montgomery County District Attorney’s Office for Montgomery County DPS to obtain their first unit. That unit still requires one person to mark points as the other enters points on the main unit.






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