The latest tech tools
The Direct Reflex Total Station is a one-person operation, operated from the transit. (Photos Weston Brown)
The robotic total station is a one-person operation, operated from the prism pole.
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Watch an episode of "CSI" or "Law and Order" and you'll get an idea of the public's perception of crime scene work today. That same public will be sitting on the jury when you prosecute your vehicular homicide case. Depending on the state, you may charge a lower felony for vehicular homicide, or you may charge something as high as second-degree murder. Regardless, the jury will look to the State to be the experts.
The jury also believes DNA evidence will be available later that afternoon, and that most of what you investigate is somehow run through a computer. They watch and wait to see what high-tech gadgets you've used to determine the facts.
Let's face it, part of what we do while presenting the facts is a show, but diagrams are a crucial part of any traffic fatality. Unlike a homicide, where bullet trajectories can be calculated on scene and the event dynamics are typically spelled out in blood and other evidence, a traffic fatality can't be reconstructed on scene. Approach and departure angles, many curves with changing radii and damaged vehicle profiles must be documented so that they can be recreated in scale for the purpose of reconstructing a collision.
You must make many other ambiguous measurements. Departure angles, for instance, are a requisite part of any reconstruction in which two or more vehicles come together in an intersection at an oblique angle. You can't measure departure angles on scene they just don't make a protractor that big.
There are many diagramming tools out there today, and they can run from hundreds of dollars to hundreds of thousands. In this article, I'll discuss just a few examples of what's currently available for measuring a scene. Each has its good points and its stumbling points, so you must make an educated decision before you buy and always have the product demo'd for your Vehicular Crimes Unit before you make that big-ticket purchase.
Tape Measures
For years, collision investigators did excellent reconstructions with tape measures, and those basic tools still have their place. Understanding the basics of measuring with a tape is very important. A good investigator can get by with utilizing two 300' cloth or nylon tapes and a few 100' and 50' tapes.
Make sure your unit has the obligatory training to document the measurements properly. The difference between accuracy and precision becomes apparent when an investigator hasn't been properly trained.
Collision evidence such as vehicle crush is often done with tape measures and can result in a fair depiction of the vehicle when completed in a quality computer-aided drafting (CAD) software package. Again, proper training on the techniques and the proper equipment (such as a plumb bob) are crucial. The scene may also be diagrammed in a quality CAD software package when the scene is measured with tapes, presenting a high-quality end product for the jury.
One tape measure pitfall: the inability to measure grades or accurately document grades in the final diagram. Rolling hills, gulleys and small canals present problems for tape measures because tape measures can measure in only two dimensions without presenting a number of logistical issues. If you work among hills, you may run across instances in which a car skidded downhill, leveled out and then continued uphill. A 4' level for the grade measurement won't suffice for a thorough and accurate speed analysis in this case without spending hours measuring multiple positions along the roadway.
Another downfall to tapes: Detectives must hand-draw the diagram once they return to the office, or manually input the data into CAD software. Either of these processes are time intensive and leave room for additional errors.
Survey Equipment
Transits have been around since the 19th century, and in the past 30 years have changed as fast as computer technology. The system for completing surveys hasn't changed much, but the technology now does all the work for you. Simply put, the operator assigns a known point where the transit is located (typically called a reference point), and the operator locates points of value and measures each based on the reference point. The system knows the angle a point of value is from north (called the horizontal angle), and it knows the vertical angle to the point, and using these two angles and the measured distance, it can then triangulate the exact position of the point of value in three dimensions.
These systems have become more and more accurate as technology has improved. Today, survey systems are accurate to within 2 seconds. What does 2 seconds mean to you and, more importantly, a jury? A circle is broken up into degrees, minutes and seconds. A machine with a 2 second accuracy means that if a point of value lies 1,000 feet away, the system will calculate its position to within approximately /10 of an inch of its actual position. New survey systems are nearly all 2-second machines.
There are numerous Chinese-made survey stations you can purchase for around $2,500 and up. In my eight years of collision reconstruction, though, I've never had an opportunity to use one of these machines and didn't utilize any during my research for this article because you can purchase a quality used Nikon or Sokkia system for around the same price point, or even less.
Nikon and Sokkia both build quality, simple-to-use systems. These systems come with the option of prism or prism-less, also called direct reflex. A direct-reflex machine can shoot a point at a range of up to 200 meters (656 feet) by simply aiming the viewfinder at the point you wish to measure. Direct-reflex systems start at around $3,500, and they turn what would have been a two-person operation into a one-person operation on small scenes.
When shooting points greater than 200 meters away, you need the prism. With the prism, the range is well over one mile. A non-direct reflex machine requires an operator running the transit (the measuring tool), and another operator holding a prism on a pole, which is held over the point you wish to measure. The system then triangulates the exact position of the point in three dimensions.
During my tenure as a vehicular homicide detective, I used prism stations. These were always able to get the job done with more than ample precision, and with a good CAD package, my diagrams were always top notch for courtroom presentations.
A direct-reflex machine can also utilize a prism to obtain measurements at distances greater than 200 meters. And an even more advanced system that uses the technology of the survey transit is the robotic total station. A robotic total station follows the prism as you move. The system maps to the prism and tracks the prism, either visually or with a radio frequency signal.
The robotic total station is a one-person operation. During the research for this article, I used the Trimble 5600. This system used a radio signal to maintain a track on the prism. The system took measurements immediately with almost no delay, and I was able to shoot points along a roadway much faster than I'd ever done with any of the total stations I've used in my real world investigations. This is an important consideration to make because while the top priority is collecting the evidence, the politicians and the public really appreciate it if you can open the road back up as quickly as possible.
The Trimble 5600 runs around $26,000. The robotic total station also uses direct-reflex technology, allowing the operator to measure points without the prism while working from the total station base.
A survey transit also offers a great deal of versatility for secondary uses. You can use one for documenting not just collision scenes, but crime scenes as well. Out at the collision scene, you can use one for completing damage profiles of the vehicles involved. By sharing the system between your agency's units, you make the purchase price more palatable.
Global Positioning Systems
Today, everyone knows what GPS is. Many people have this technology in simple, very small handheld devices. Using GPS technology to map is nothing new, but understand what's available to you should you choose to use this technology for your investigations.
There are three levels of GPS mapping equipment available on the market today. The primary difference between each level is the number of satellites the system can access in order to find its location on Earth. The basic systems look at only two types of signals, L1 and L2. The intermediate systems give the operator access to L1, L2, L2C and GLONASS. (L2C is a more accurate form of the L2 signals, and GLONASS is the Russian GPS satellite system.) High-end systems also use L5 signals, which are due to begin broadcasting some time between 2009 and 2011.
With a GPS system, the more satellites available, the more accurately it can pinpoint your location and the less likely you are to receive no signal. The mid-range units will get you to within +/- 1 cm of your actual location on earth. Considering your typical tire mark measures roughly 5" 7" inches wide, that gets you well within your accuracy and precision needs.
The system I used in my research took 3 4 seconds to lock the measurement for each point measured, considerably longer than the robotic total station took. When multiplied over the 500 600 points or more you might have to measure on a scene, it will add up.
A primary consideration for GPS systems is the line of sight between the GPS system and the satellite. Working under bridges or near tall buildings presents issues with the GPS system no matter how many satellites you have access to. If you're working under something with significant structure, or even in very close proximity, it may limit your ability to access satellite signals.
Therefore, when thinking about purchasing a GPS system, consider the environment you'll use it in, especially if you want the system to have a dual role. If you're looking for equipment to assist your homicide unit and your vehicular crime unit, for example, this may not be the best system.
Basic GPS systems start around $35,000, mid-range systems start at around $48,000 and the high-end systems start at around $56,000.
Scanners
Scanners are a relatively new survey tool to the market. They're the top-of-the-line of survey tools, from a technology standpoint.
The FARO Laser Scanner, for example, is an excellent high-tech tool that allows for a one-person operation. This scanner utilizes a set number of globes placed within the scene. The scanner then begins sending out laser signals, measuring the distance to millions of points and creating a picture-like 3D diagram of your crash or crime scene.
The output from the scanner is then downloaded to your laptop computer on scene. Because the system measures millions of points, you'll need a fairly powerful computer to run the software and view the diagram. The FARO comes with the FARO Scene Forensic Package for diagramming, an inclusive CAD software package.
Scanners are fairly limited in range, allowing for around 200 300 meters of scene collision. Unlike the survey transit, this means you'll likely need to move the scanner down along the scene. This is simple to do. Allowing the scanner to view at least three of the globes placed in the scene originally will allow the scanner to orient itself to its new location and continue to scan. You may find yourself moving the scanner multiple times on large scenes, and at very small scenes in which the scanner may have obstructions, such as indoors.
Trimble also makes two scanners: the 6X, which is a true standalone scanner similar to the FARO, and the VX, which is a 1-second total station with scanning capabilities. These systems run from $70,000 $100,000 and above.
Lasers
You can also use the same system many traffic enforcement units already have. Laser Technology Inc. (www.lasertech.com) offers a device an officer can operate as a speed enforcement tool and, when responding to a crash scene, also use (with some additional tools) to map the scene three dimensionally. Using the LTI laser with an angle encoder and data collector is a one-cop operation utilizing the same technology found in other survey equipment.
The benefits of such a system include portability, versatility and accuracy. (You may be able to carry it on a police motorcycle.) The drawbacks to such a system include range and nighttime use on large crash scenes.
Final Thoughts
Each of the systems discussed in this article offer a wide variety of benefits, and each has its drawbacks. Always have any of this equipment demonstrated for those who will be using it because it's only as good as the operator, and a thorough understanding of the technology is crucial for litigation.
Only you and your vehicle-crimes unit can decide what system is right for you. From tape measures to scene scanners, there are many options, including more that I don't have the space to discuss here. The roadway is not the only thing you'll document at a fatal collision, and you should think about what your team documents and, most importantly, how they want or need to document it.
Time is always of the essence when a roadway is closed down. When homicide is called out, the crime scene is usually relatively small with a limited number of people affected by the closure. When complex accident investigations are conducted, however, major city arteries are often shut down, affecting thousands of people for a number of hours. The documentation is just as important, but anything you can do to reduce the time you are actually on scene helps significantly.
