Map crash scenes quicker, safer

For years, this country’s roadways have been a recurring scene of death and destruction due to fatal car crashes.  The National Highway Traffic Safety Administration estimates that about 43,000 people are killed in fatal car accidents each year in the United States.

How these fatal crashes happen is what keeps traffic investigators and trained crash reconstructionists busy every day. They must map the scene evidence to determine the likely events that may have caused the crash.

With more crowded roadways and more crashes, investigating, measuring and diagramming these scenes can pose a danger---both to anxious motorists forced to wait for a crash scene to clear, and to the investigators working the scene. Since a roadway may be shut down entirely, or, more often, with just one lane left open for traffic in both directions, it’s easy for secondary vehicle accidents to occur among drivers anxious to get moving again.

Because investigators frequently must work a cramped crash scene close to moving traffic, the potential for serious or fatal injuries is always present. The total station, which has been the predominant instrument used among crash investigators to map scenes, has proven effective for mapping scenes  accurately and quickly, allowing for quicker scene clearance, making investigations safer. 

Originally designed for surveyors, the total station has been conveniently adopted for use at crash scenes due to its high accuracy and ability to capture large chunks of evidence data points. Basically, a total station is an electronic/optical instrument with an electronic distance meter (EDM) for reading slope distances from the device to a particular point.

The total station can determine coordinates of an unknown point relative to a known coordinate if a direct line of sight can be established between the two points. Angles and distances are measured from the total station to points on a roadway’s crash scene. The coordinates (X,Y, and Z or northing, easting and elevation) of surveyed points in their relation to the total station’s position are calculated via trigonometry and triangulation.

Once the points are all mapped, they are then fed into a data collector connected to the total station. From there, the data can be fed into a crash scene diagramming program to create a 2D or 3D diagram.

Battery of total stations used In Las Vegas

Las Vegas, Nev., aside from its image as an entertainment and gambling mecca, has a plentiful share of car crashes. The city’s population has exploded in the last 20 years. And tourists stream into and out of town constantly. “That combination makes for a more accident-rich environment,” says Bill Redfairn, a veteran detective with the Las Vegas Metro Police Department’s (LVMPD) Fatal Crash Investigation Detail. He notes that the Detail investigates 200 to 300 serious injury or fatal car crashes a year.

This explains why LVMPD has an impressive array of total stations for investigating crashes. These range from older models to the latest in total station technology, which today includes robotic and GPS total stations.

In the 1980’s, LVMPD did not have total station technology, using, instead, tape measuring wheels and regular tape measures, and even generating crash diagrams by hand. About 15 years ago, it purchased two Nikon total stations. But batteries wore out quickly and it was hard to replace them. So, although these units are still used today, the LVMPD turned to Sokkia total stations, upgrading through the years to the newer technologies.

The LVMPD’s Fatal Crash Investigation Detail usually assigns two detectives (primary and secondary) and a sergeant to each major crash. The supervisor (primary detective) has always run the total station. Earlier total stations required two operators--one to run the total station and another to hold the prism pole over points of evidence so they can be recorded and relayed back to the total station.

Remote Control Devices Speed Up Scene Mapping

“We wanted something that could be more efficient and get the supervisor out more quickly by starting to map the road himself, and by the time he was done the secondary detective had the evidenced mapped,” Det. Refairn explained.

Initially, the LVMPD acquired Sokkia SRX series robotic total stations. Robotic total stations allow the operator to control the instrument from a distance via remote control. This removes the need for an assistant staff member as the operator holds the reflector and controls the total station from the observed point.

The Sokkia SRX series are fully tracking and auto-pointing robotic total stations, with on-demand target reacquisition and reflectorless EDM (electronic distance meter).

When total stations are referred to as being “reflectorless,” this means the device can measure objects or points without the need of placing a prism a those points. This advancement saves tremendous time for the total station’s operator, and it improves safety while mapping a crash scene.

GPS helps map longer scenes

The LVMPD’s Fatal Crash Investigation Detail prides itself on being techno-savvy, which is why in 2010 it added three new Sokkia GRX1 GNSS systems--GPS total stations-- to its total station arsenal. The GPS total station is becoming very popular among total station users since it can give position of a point accurately anywhere on the globe. The GPS can measure base lines with high accuracy, and controls points with no need for line sight. The GPS total station also can map far greater scenes and distances than more conventional total stations.         

Traditionally, total stations have worked on the principle of signal reflection off a line of sight between the total station and a prism reflector. The GPS total station is effective for establishing control points because its antenna automatically finds these via satellite signals, thus giving a fixed position at a crash scene.

The GPS receiver provides high speed of supervision, higher accuracy (even in harsh conditions) and low power consumption. These total stations also are lightweight, and can be used on a tripod, in a backpack, or on a car or other mobile objects.

Units Complement Each Other

What Det. Redfairn values about his department’s total stations is that they can all be used together, and complement each other. For example, he said, “Neither one of the robotic or GPS total stations is the perfect machine, but when you have the two of them together you’ve almost got the perfect system. Where the GPS can’t go because of limitations (GPS units require open sky since they are satellite-based), the robotic total stations can,” Det. Redfairn said.

The detective notes that combining robotic and GPS total stations allows mapping of very large crash scenes. “You can have two or three people measuring the scene, then you can marry the data collected from these total stations to create a diagram,” Det. Redfairn said.

With these significant strides in total station technology, are traffic investigators safer as they measure the still hectic, distracting and perilous crash scenes present today? Det. Redfairn believes so.

“It’s not so much the safety of the operator at the scene, because he’s not going to be shooting from real far away, hence, being out of the way of bypassing traffic,” Det. Redfairn said. “But it allows the scene to be cleared more quickly.” And this, argues Det. Redfairn, is where safety levels are heightened.

Safety a Factor in Total Stations’ Purchase

Sgt. Sarah Crane of the Utah Highway Patrol would agree with Det. Redfairn’s assessment of total stations and their contribution to increased safety for crash scene investigators. A nine-year highway patrol veteran and a trained reconstructionist, Sgt. Crane uses a Topcon 3100 series reflectorless total station.

Utah Highway Patrol racks up 250  fatal crashes per year. Because the state is so spread out, the highway patrol uses 17 of the Topcon total stations, which are distributed among several regional sections throughout the state for use by the patrol’s crash investigators.

Sgt. Crane said officer safety was a factor in buying the Topcon 3100 series “because with the reflectorless (models) we don’t have to have an officer in the roadway while mapping a crash. A lot of times we have live traffic and leave the road open so cars can still go through,” Sgt. Crane said.

By upgrading to the newer total stations, highway patrol crash investigators across the state can always map scenes easily and quickly since they have access to one or more of the Topcon units. This is especially helpful to those troopers who must investigate longer crash scenes that develop  in rural areas.

Not just safer, devices give more data

Safety is the main challenge that the National Association of Professional Accident Reconstruction Specialists (NAPARS) sees relative to mapping crash scenes. Says NAPARS President Chuck Veppert, “Anytime you’re interacting with traffic, there’s a chance you could back up traffic and, in fact, end up with another traffic accident. That’s our main challenge--to see how safely we can do it and not to cause another traffic accident,” Veppert said.

Related to safety, of course, is the time it takes to map a crash scene, which Veppert feels must be condensed to ward off the potential for secondary traffic accidents. With older mapping technology, such as tape measures or roll-a-wheel tapes, it took long stints of time to measure crash scenes. “Not only did this place officers in danger for whatever period of time they were on the roadway, but it also meant that more than likely you were going to take less measurements than what we do nowadays with the total stations,” Veppert said.


Although it might take an investigator the same amount of time to map a crash scene using a total station versus a tape measure, he can capture up to 50 times as many measurements, Veppert argues. “So, we can be much more accurate in that same amount of time,” he said.

Shooting distances of total stations have improved as well. Veppert noted that the new Sokkia 50RX Series reflectorless total stations have an extended measurement range of up to 400m (1,310 feet). In addition, a company news release on this product announcement says variation of measurement time due to different ranges and object types has been reduced by 30 percent to increase total measurement speed.

“This is a great improvement over the early reflectorless units,” Veppert said of the total station’s extended measurement range.

Valuable time saved

Saving time with measuring crash scenes is one of the biggest benefits of using today’s more advanced total stations. Not only does this allow quicker scene clean-up and boost safety, but it helps reduce the cost of lost revenue for detained motorists.

For example, Det. Redfairn of the Las Vegas Metro Police Dept. indicates that when investigators used older total stations, it would take between four and five hours to map a typical fatal accident scene. “When we got the robotic total stations, it went down to about three hours,” Det. Redfairn said. “Now, with the GPS, it’s taking two hours to two hours and 45 minutes.”

Shoot scenes off roadway

For Neil Trantham, a Nebraska State Police officer and owner of Nebraska Accident Reconstruction, setting up a total station for a crash scene off the roadway is paramount. He finds the most dangerous place to be at a crash scene is where the officer directing traffic is located, at the far end of the accident scene. “Because traffic is coming along at highway speed, people aren’t paying attention when they come up on the scene, which causes a lot of secondary rear-end crashes,” Trantham said.

Trantham prefers to set up a total station between 50 and 100 feet off the roadway. This approach, he reveals, makes it easier to locate the operator of the total station’s reflector and to aim the total station to map the scene. “Safety is number one,” Trantham said. “Plus, when you’re at the instrument itself, your focus is not always on the traffic and what’s going on around you. You can focus on the number one thing at hand and that’s mapping.”

Although some vendors and users may claim that the latest high-end total stations are one-person operational, Trantham disagrees. These are one-man systems, he explains, but the operator is physically holding the

pole and watching over a point of evidence, pushing a button, capturing that point and coordinates, and, thus, still potentially exposed to traffic in the roadway.

Trantham’s crash reconstruction consultancy uses three different types of total stations--Sokkia 600 Series non-reflectorless, reflectorless models, and recently purchased Sokkia robotic total stations.

Using a reflectorless total station, the operator can capture reflectorless points on the roadway, but the total station must be set up fairly close to the roadway. However, Trantham said, “You’re not going to capture points too far down because of the angle at which you’re capturing points. The farther away that angle is from the instrument, the shallower the angle will be. And this means the less confident you’ll be that you’re capturing the evidence.” So, the operator may have to move the total station several times to capture points of evidence, especially if the scene is a long one.

Operator skills still pivotal

Certainly the latest total station technology is changing the way crash scenes are now measured. But the quality of a measured scene really falls back on the skills, expertise and techniques applied by the total station’s operator. That is the opinion of Trantham, the Wisconsin reconstructionist.

Trantham said the operator needs to be comfortable with his total station, set it up at proper height, and know completely what kind of key evidence is needed to have a properly mapped scene and, utlimately, scaled diagram. It’s all a delicate balancing act.

Trantham also feels it’s not essential to try mapping every piece of evidence after first arriving at the scene. “Officers mapping a scene should realize they can capture much of the evidence on the day of the crash, then come back later, at a more convenient time, to capture roadway evidence,” Trantham said. “As long as they put down some permanent points (i.e., concrete nails), they can merge the roadway diagram and evidence diagram. That’s the key. The quicker you can secure that scene, the safer it is for motorists and officers,” Trantham added.

Robert Galvin writes on law enforcement and other topics from Oregon City, Ore.