Anatomy of an accident

Accident reconstruction expert Arnold Wheat works the scene of a big rig wreck in Colorado.

The wrecks were lying in snow and ice, and in accident reconstruction, ice changes everything.

Two tractor-trailers had collided in a snowstorm, and each driver blamed the other. There were neither skid marks nor any other tell-tale signs on the white, icy road. Engine electronics data can often be used to determine speed, braking and other factors in a crash, but on ice wheels can slide and/or spin, often making it impossible to define the exact impact situation.

On ice, more throttle may not increase speed and less may not decrease it. There can be evidence brakes were applied, but the lack of skid marks mask brakes’ effectiveness in stopping the rig, a rig that may also be sliding and not always in a straight line. An antilock braking system on ice can also confuse the issue as it battles the ice and brakes to try and keep wheels turning.

It appeared that this case might come down to one man’s word against another’s. But accident reconstruction expert Arnold Wheat got lucky.

“My client’s driver was accused of crashing into the other rig at an unreasonable speed for the conditions,” says Denver-based Wheat, author of the Accident Investigation Training Manual and specialist in investigating big rig wrecks. “The accident scene showed that our driver’s tractor and the other rig had indeed crashed together, making the other driver’s story at least one of the possibilities.

“There had actually been a series of collisions in the storm, but the two vehicles in question were the most significantly damaged. We downloaded the electronic control module data from our client’s tractor engine, and it supported our driver’s explanation. It showed he was traveling 28-31 mph for up to a minute then began a gradual deceleration, coming down in 1-to-2 miles-an-hour increments, 30 – 29 – 28 – 27 – 26 and so on, slowing at about a mile an hour per second. The greatest drop in his speed in one second was two miles an hour. It was a controlled deceleration, almost coasting to a stop.

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“The other driver alleged that this driver had rear-ended him at close to 30 mph in the snow and ice, causing him to lose control and jackknife. Our driver claimed the other driver had slid into him after losing control. I was now able to tell my client I had found evidence of a steady, controlled deceleration and stop and insufficient speed at impact to cause the damage in the wreck. We could now argue that the other truck had lost control and slid into ours.”

Accident reconstruction can make the driver look good or bad after a big rig wreck, depending on his actions.

“It’s a two-edged sword, certainly,” says Julian R. “Bucky” Beaver, veteran ex-Georgia State Trooper. Beaver founded Southeast Collision Analysis, based in Brunswick, Ga., in 1990, and focuses on big rigs. “If you are in the right, accident reconstruction has the potential to back you up all the way and prove what you say is true. But if it was your fault, you will be almost certainly found out if we do our work right.

“Accident reconstruction is a sophisticated process, but the science is incredible today, and combined with the experience of a top man in the field, exactly what happened will be discovered provided there is adequate physical evidence.”

According to Wheat, accident reconstructionists are mainly interested in three things: the vehicle, the driver and the environment (weather, road surface, etc.). No matter who their client, they look only for details that help explain what happened physically. They may, for example, find a driver’s actions erratic and record them, showing the effects of each move. But they would not make a determination on whether that driver were drunk or a heart attack victim.

Accident reconstructionists like Chris Medwell of Bloomberg Consulting in Gulf Breeze, Fla., another big rig accident specialist, say their profession must remain impartial: “We just do the physics of it,” Medwell says, “whether the client is a trucking company or someone who has been injured by a truck. I don’t take a certain side or position but find evidence – whatever it may be.”

Reconstructionists work in a way much like coroners. In a murder case, a coroner may determine the cause of death was a bullet, but another agency will determine who fired and why.

“The coroner can say the bullet came from this direction, at this angle, at this distance from this gun,” says Medwell. “He can say this is the damage it did and how it did it in what order and on what timeline, and so on. But he doesn’t investigate, say, who the shooter was, or why they did what they did. In the same way we try to explain exactly how a wreck occurred.”

The experts who examine the people involved in wrecks, including the intense crash investigations done by the National Transportation Safety Board (see “The Feds Dig Deep”), are experts in human behavior and psychology rather than crash reconstruction.

Most reconstruction is done for legal or insurance purposes. A trucking company client needs to be given all of the pertinent details, whether their driver looks good, bad or neutral. “I may find evidence that clearly shows my client’s driver was completely innocent, totally in the right. If my client is responsible – and I prove it – the company might be able to save a long, costly court battle and settle the matter,” says Medwell. “They will know what has gone wrong and may be able to prevent it ever happening again. For me it’s not a matter of being an advocate the way a lawyer is.

“We also have to answer a lot of ‘what if’ questions after an accident,” says Medwell. “What if someone had been wearing a seat belt? What if someone had not been speeding? So in addition to finding out what happened we are also trying to find out what might have happened. For example, in the case of injuries, how much damage was caused by a crash and how much damage caused by not wearing a seat belt.”

Finding the evidence
The first priority for accident reconstructions is speed – not how fast the vehicles were traveling but how quickly the reconstructionists act to gather evidence.

The problem with traffic accidents, says Wheat, is that they happen on public highways.

“Police or sheriff’s departments want to work that accident for 30 or 45 minutes and get the road open again, and once that happens the evidence is going to be gone,” he says. “At a murder scene you can seal a building, but you can’t seal a public road for long. The first thing is to try to stabilize the scene: set up flares, tape, triangles; talk to as many people on the scene as you can. Some will be eyewitnesses and some will have seen very little, but it is important to reach as many as you can, because what they did see may become important as you proceed with the investigation.”

ATA Associates, a Houston-based leader in the big rig wreck reconstruction field, has quick-response teams ready to go anywhere in the country within hours, and Wheat and Medwell are packed and ready at a moment’s notice.

“Evidence deteriorates at the scene very quickly,” says Beaver, whose company has five satellite offices in the South to get to accidents as quickly as possible. “Some of it is simply lost or hauled away by law enforcement. The first thing we want to figure out is how did it happen, who hit whom and where, then figure out the other details such as speed.”

Law enforcement agencies sometimes have crash reconstruction experts, says Wheat, but their official accident reports, while accurate, may not be as detailed as specialist reports.

A motor carrier officer will come to your truck wreck if it is serious enough, says Medwell. “He will inspect the vehicle, and he may find, say, three brakes are out of adjustment. That report may come up in court – the officer can attest to the brakes being out of adjustment, but he can’t tell you how that affected braking performance in the circumstances of the crash or how it affected the vehicle’s accident dynamics. That’s what we can do.

“Poor brake adjustment basically affects stopping distance, but it’s possible stopping distance was not a factor in the crash – say the driver had no time to hit the brake pedal. Yet an inspector telling a jury three brakes were badly adjusted could be influential unless we can show it had nothing to do with the crash.”

Accidents are rarely black-and-white, but the police version usually is. The police are looking to see if someone committed an offense, says Medwell. “The officer needs to know if he should charge someone and if he has evidence to prove what he is charging. Did someone run a red light or cross the center line and cause an accident? If you make a left turn and a motorcyclist runs into you, you will probably get a ticket for an illegal turn. That’s a simple police case. But I might be able to show from the crash evidence that the motorcyclist was doing 100 mph in a 30 mph zone and so when you made the decision to turn left, it was reasonable to assume the motorcyclist was doing something close to the speed limit. This can also affect things if the motorcyclist decides to sue you.”

If a driver’s version of events doesn’t seem to fit with the evidence, says Wheat, it is not reasonable to assume the driver is lying. There has to be investigation, because sometimes the evidence itself “lies” – that is, it is misunderstood, misinterpreted or incomplete.
Medwell cites a basic example: “I’ve had truckers move after a wreck – for safety reasons – and the police take their parking spot as the point where they stopped after the wreck. From that point you’ll get an inaccurate picture of what really happened.”

Instincts and experience, says Beaver, are valuable guides, “but in the end we have to have scientific proof of what happened to give an opinion. To begin, we try to physically reposition the pieces. Let’s says there’s a gouge in the road. We can figure which part of what vehicle made it and place it in the exact position where it struck the road. Then we can reassemble the other pieces around it so we have the scene at impact. Some of that is experience and even instinct, but in the end the pieces must fit, and there must be a physical explanation as to why they are where they are.”

The accident reconstructionists must also gather evidence about the vehicles themselves, pre-accident. The truck’s crashworthiness, crash dynamics, crash sequence, vehicular dynamics, fires, tires, frames, collisions, visibility, systems, articulation, driving techniques, load shift, maneuverability, design, vehicle response, restraint systems, critical speeds, traffic engineering, DOT standards, rollover or rollover propensity must all be considered to be sure a reconstruction is accurate.

Reading the evidence
Experience and computers mingle in the understanding of one of the key accident clues – and most often used pieces of evidence in court – skid marks.

“You need all of your experience, intuition, computer skill and detective ability to work out skid marks,” says Beaver. “You have to know how to interpret and know what to look for and how to prove it. Is it a skid caused by braking or sliding? In the latter case were the wheels in line or might they be sliding a little sideways? What sort of tires? What sort of load (weight)? What sort of transmission? What ratio in the rears? You have to ask if any given skid mark was made by a single tire or even a single vehicle. We had a case where a big rig and a pickup wrecked and the trucker was charged after skid marks were used as evidence of excessive speed. But we were able to show that part of the skid marks in question were actually made by the pickup.”

Medwell cites a hypothetical example: “Let’s say you’ve got an intersection and a car drives underneath a trailer. Crash. The trailer wheels lock up and create skid marks when they come into contact with the car. The truck driver feels the impact and reacts, hitting his brakes. But his tires had already been leaving skids marks from the impact point – so the skid marks will indicate how long the wheels were not rotating and were skidding, but they don’t accurately tell you when the truck driver hit the brakes. The beginning of the skids was not caused by his braking. But if you don’t find this out, you might decide the truck – based on the length of the skid mark – was going much faster than it really was.”

Or take this everyday example: While ABS lets drivers stop fast in a straight line, a truck can still jackknife, and a driver fighting a jackknife will stay off the brakes and only apply them after he is in control. When he does, a skid mark will appear. But it would be a mistake to suggest the trucker did nothing to control his truck and avoid a crash until the skid mark shows him hitting the brakes.

Likewise, determing speed can be difficult to get right.

“You do have the ECMs, skid marks, witnesses and the evidence of impact, but there are other factors,” says Beaver. “Speed readings come from the drive shaft, which means an overturned tractor-trailer may indicate movement because its drive shaft is still spinning. A tractor in a collision may be pushed ahead even while the drive shaft is stopped.”

ABS also can complicate things when it comes to braking, skids and wheel rotation. It may, for example, cause the speedometer reading to be off – the wheels are turning under heavy ABS braking, but you do get some wheel slip and some sliding. Under heavy ABS braking, the drive shaft can be turning out of synch with the wheels, making speed determination difficult.

Speed is a vital component for another reason. How fast a driver reacts to a problem can be a factor in a collision, or at least in the insurance and legal debates that can follow one. If the trucker is speeding, or if a vehicle driving into his path is speeding, expected reaction times can be greatly diminished. When you work out how much time it took a truck driver to react to a situation, you can compare it to the average times in controlled studies that are considered the standard.

“Unless a driver was totally not paying attention and didn’t react until way too late,” says Medwell, “he’s probably not going to get into trouble for reaction time. But if the normal reaction time is two seconds and he takes six seconds, there needs to be an explanation for the disparity. Had he been drinking? Was he fatigued? But that’s for someone other than me to find out.”

How to Avoid a Wreck
“It’s very rarely that equipment failure causes an accident,” says Southeast Collision founder Julian R. “Bucky” Beaver. “It does happen, and when it does poor maintenance is more often the cause than freak accident. After a wreck, a driver will often blame brakes, steering or tires for the crash, and sometimes they are in fact to blame. Other times the driver is simply trying to explain because he doesn’t know yet. A lot of times they don’t know until they know what we have found out.”

According to Bloomburg Consulting’s Chris Medwell, most accidents are caused by driver error. “That doesn’t mean tractor driver error only. Usually an error by one or both drivers,” he says. “Distractions such as talking on a cell phone, listening to the radio or even reading a newspaper can cause wrecks. A lot of the time we never hear about it unless the driver admits it, and a lot of the time we don’t know the underlying reason for driver errors.”

Medwell suggests two key practices to help avoid accidents: maintain your equipment and keep your following distance.

“Following too closely is a potential problem, especially if you are following other trucks. There are fuel savings, but the risk is too high,” Medwell says. “It can turn a minor accident into a major one. The following driver is not actually driving, he’s basically just watching the tail lights on the rear of the trailer in front of him and not the road and the environment around him, so there’s a kind of ‘inattention blindness.’ You are looking a few feet ahead, not hundreds of feet ahead.

“There were two trucks running together, and they came up on another truck parked on a curve in the road, but not on the shoulder. The driver of that parked truck had stopped to check his load – he put his flashers on, but he didn’t roll onto the shoulder because he thought the load had shifted and an uneven shoulder might cause him to lose the load. The first truck bearing down on him saw and swung out to get by him, but the second truck following the trailer didn’t have time to react and went into the back of the parked truck. The tailgating truck was team driven and both drivers died. We don’t know what happened, but inattention blindness is the likely cause.”

The biggest thing in accident prevention, says Arnold Wheat, author of the Accident Investigation Training Manual, is to have a constant awareness that an accident can happen at any time or place, whether you are driving with a high degree of vigilance or if you are not really focused on driving.

“Too often a driver is moving along with all sorts of thoughts in his head about everything but driving. It is easy to be complacent in the modern plush luxury of many of today’s vehicles, with all of their own distractions,” Wheat says. “We hear that most accidents occur within 25 miles of home. Why? Because we’re very comfortable in our neighborhoods. We see familiar people doing familiar things in familiar places, we know them and have a history with them and they attract our attention and engage us. There is a level of expectation. But the everyday can fool you. You stop thinking about driving and your mind wanders. I think it’s possible that truckers who run to the same places a lot and get into an accident do so because their familiarity with their surroundings causes them to become less vigilant about driving.”

High Tech and Low Tech
Software and old-fashioned detective work go hand in hand when dissecting a collision

Houston-based big rig wreck reconstruction firm ATA associates will rely in some cases on photogrammetry, a 3-D measuring technique that uses photographs taken from at least two different locations to triangulate spaces, dimensions, widths and areas. In other words it can help create a site map of an accident from a picture, telling investigators such things as the length or width of a skid mark.

ATA also uses sophisticated electronic surveying software, which records dimensions, elevations and locations of a structure such as a roadway and can help create a precise multidimensional map of an accident scene. Once all the data on an accident has been collected, and investigators are sure they know what happened and how, reconstructionists turn to computer-based tools such as PC Crash, WinCrash or PC WinSMAC to create an animated version of events on a computer.

These programs are precise. Vehicles and people in the animation will be to scale and so will vehicle paths and speeds and the layout of the accident environment. Software can be precisely programmed to allow for such factors as make and model of truck, axle loads and ratios, cargo load, brake force, tire pressure and size, weather or road conditions. They can be programmed to show how a vehicle reacted.

In the case of a fatal wreck in a construction zone, Chris Medwell used a computer for another purpose. The wreck occurred, he says, where two lanes were funneled into one by orange cones.

“Most vehicles go to the right lane fairly early and slow down, especially the less maneuverable big rigs, but there are always some, usually four-wheelers, that wait until as late as possible to gain as much ground as possible. Those vehicles may be going faster and may change lanes suddenly to get into the right lane and then slow very quickly.

“In this case a tractor-trailer was approaching that single-lane point, and a straight truck was behind him. They were traveling 40-45 mph with no problems. The straight-truck driver looked away, he said, for a second or two, then looked back. At this point something caused the tractor-trailer to brake hard, so hard its driver was concerned about being rear-ended, and as he braked he moved toward the shoulder so no one would run into him.

“At this point two four-wheelers in the left lane braked and moved in between the tractor-trailer and the straight truck. The straight-truck driver said when he looked back he had no room left in front of him, and he hit the back of the second of the two cars that had pulled in between him and the tractor-trailer. The straight truck started moving off to the right side of the road and onto the shoulder and the car he had hit was still in front of him. It had hit the car in front of it out of the way, and then it was crushed between the front of the straight truck and the rear of the tractor-trailer.

“The straight truck driver was charged with criminal negligence causing a homicide. We created a perfectly accurate accident simulation that showed that the cars could have come between the tractor-trailer and the straight truck in as little as two seconds, meaning that the driver may have looked away for as little as two seconds. It was then possible for our client to argue that a two-second distraction from the road in front of the driver was not gross negligence.”

Not all reconstruction work is computerized. For example, Arnold Wheat uses toys to demonstrate his points in court.

“There’s a sort of ‘wow’ factor when you bring out an accident animation, and in court a jury can be overwhelmed, losing sight of some of the simple points we have to make and basically being enthralled by a movie,” Wheat says. “So I use die cast truck and car models, to-scale replicas, exact models of the real thing, exact models of the scene. Jurors can see as I place them and move them the basics of what I am trying to get across to them. The jury can see photographs and the models basically show them a 3-D version of how it happened and how the damage was caused.”

Southeast Collision’s Gary Corey insists “there’s still a lot of tearing a wreck apart with tools or your hands, and a lot of physics and math in this work. There’s a lot of measuring and you have to rely on your imagination a lot to weigh various possible scenarios in the deductive process. You often have to break a vehicle down into parts to find the truth.”

Much of that work for Southeast Collision is done by Ben Mosley. “We had a case where a car collided with the back of a tractor-trailer,” says Mosley. “The truck driver said she was driving at 50 mph and couldn’t go any faster because she couldn’t get beyond ninth gear. A state trooper drove the truck after the crash and found he couldn’t get more than 15 mph because he couldn’t get past low fourth gear. I took the inspection plate off and reached in and found metal shavings. I took the top off and took out the shift forks and found where gears should have been the metal was as smooth as a soda can – so they were both right.

“She had gotten past fourth when she drove, or may have skipped fourth, but then ran out of transmission fluid and that finished destroying the gear by the time the trooper drove the truck. The driver said she’d added fluid before her run, but it didn’t help. We found out why. A transmission cooler cable had been improperly reinstalled after some maintenance and it was rubbing against the drive shaft, and when it wore through, the fluid all leaked out. In the accident the driver was accused of going too slowly – something the trooper at first seemed to confirm, but her story about being able to get 50 mph was also true.”

In a case where a trucker started out as the “bad guy,” Medwell used some basic detective work to find a new explanation. “This case turned 180 degrees in the middle of the investigation. A tractor-trailer overturned and ended up on top of an SUV.

“A mechanical fitness report on the truck found excessive play in the steering wheel and broken brake lights. Police said the mechanical problem – excessive steering play – may have been a factor. The tractor was a cabover, and we found damage right in front of the driver’s seat, and the firewall and the windshield were crushed in. The brake pedal and the treadle valve were damaged. In a cabover the steering column goes up and forward to a joint, then back toward the driver.

“We found that all the excessive free play the police had found in the steering column had come from damage caused in the accident itself. The brake lights had also gone out during the accident. We proved there were no mechanical problems with the truck at the time of the accident, and that was our only job.”

Old-fashioned detective work is still required in other cases. Reconstructionists will go to the crash site at the same time of day in as close to the same weather conditions they can find to see if there may have been factors not found when investigations were done at another time of day. Might the sun have been perfectly aligned with the road and coming over the horizon directly into a driver’s eyes at the time of the accident? Might pooled rainwater have been splashed in a wave into his windshield by another vehicle?

Sometimes reconstruction cannot find 100 percent of the details of what happened. And even with strong reconstruction detail, what happened can be argued between insurance companies or in a court of law.

Wheat says he recommends truckers take pictures of accident scenes. Some police departments don’t take pictures, and many don’t have specialist officers on the scene.

“A lot of people assume they will,” Wheat says, “and if there are no pictures it can make it harder to show what happened or to defend yourself.”

The Feds Dig Deep
An investigator with the NTSB tells Truckers News how accidents are chosen and examined

Dennis Collins is a senior accident investigator with the National Transportation Safety Board, making him part of some of the most comprehensive accident investigation and reconstruction efforts ever made in the United States.

When it comes to highway accidents, the NTSB chooses to look into only so many, making their choices based on how valuable the outcome of their work can be in improving our roads and transportation system.

Truckers News: How do you keep track of accidents?

Dennis Collins: There are a number of ways we can be notified of an accident, including tractor-trailer accidents. We have a communications office that monitors news, we have direct reports from carriers, we have reports from police departments and other law enforcement agencies and we have a call center.

TN: How do you choose which ones to investigate?

DC: The first thing we are going to do is ask a series of questions. We ask what is the level of public interest; have we done something like this before, in which case we might not find anything new and valuable, for example a drinking and driving accident may only provide us with a repeat of results we have seen in previous investigations; can we make a difference, in other words could our findings help save lives in the future or make roads and transport safer in the future; what will our work do to help the public? We may look at 100 accidents a day trying to find one that fits the criteria.

TN: Then how do you proceed?

DC: We immediately contact local authorities, parties to the accident, people treating people, vehicle owners and witnesses. At the same time we assemble a team to investigate, six to eight people to a team, depending on which specialists we need. They may be from a number of different parts of the country, and they are dispatched as quickly as possible to the scene. Our goal is to gather all perishable information as soon as possible. At the scene we will get together with local experts.

TN: What is your objective?

DC: We are not trying to assess blame, just to find the cause of the accident. We aim to make a decision on probable cause. If there is criminal liability, that will be something for another agency – state or local law enforcement usually – to take up. We have a narrow job definition, and we are limited by Congress in our mission. We can’t be called as expert witnesses because of a statute designed to protect our independence.

TN: How are your investigation teams compiled?

DC: A survival specialist will look at how the safety features on the truck performed. Human-factor specialists will look at how the driver performed. A motor carrier specialist will look at the records and practices at the carrier. A vehicle specialist will look at the mechanical operation of the vehicle prior to and during the accident. An agent in charge will coordinate their work and their relationships with local and state authorities and other people involved in investigating the case. We will invite anyone who can help to come talk to us and tell us or show us what they have. The NTSB has subpoena power, so we can call people to come tell us what they know.

TN: What is your specific role?

DC: My expertise is human performance. I explore what the driver was seeing and feeling at the time of the accident, his or her training, the decisions that were made or not made and the decisions that should have been made, was alcohol a factor and so on. I look at every aspect of the driver’s life and experience, and everything he did that day. Even if I find something, for instance maybe alcohol was a factor, I keep looking because an accident is a chain of events, and one simple answer is rarely enough to explain it. Sometimes I am the advocate for the driver; I can go to bat for them, especially if the wreck was fatal, if the evidence is there. Obviously when we get the physical evidence of what happened, we are able to see if the driver could have recovered but did not or whether things were beyond his control.

TN: How deep do you dig?

DC: Very. We look at every possible factor in an accident. It was cold, so was the road perhaps icy? If there is evidence that there was no ice on the road, that factor is excluded only then. Once the exclusions are complete, we concentrate on everything that is still a potential factor. It’s an exhaustive process. From the wreckage we will take every measurement we can. Things like steering, braking, air pressure, acceleration are all checked to see if they could have been a factor. Was the sun’s glare a factor? We look at the geometry of sun angles. We study autopsy reports to find injury patterns. We can spend two weeks at a scene gathering evidence and information, and it can be a year or a year and a half after that before our report is complete because the process is exhaustive. The mass volume of information is what causes it to take that much time. There is no way to do it faster and still do it right.

TN: What is the goal of this work?

DC: Our reports are made so that people can use them to improve safety in the transportation system. Something in the system, in the industry, failed and we need to try and help fix that failure. It could have been the road, driver training, maintenance, vehicle failure or something else. We make recommendations based on our report in the hope that if they are followed, the industry’s safety will improve. In a recent case the maintenance on manual brake slack adjusters was being done automatically, and this caused a problem that led to an accident. So our recommendations urged carriers to change that practice if they were
doing it.

You can investigate NTSB crash reports, including big rig wrecks, at Click on “Accident Reports,” then on “Highway Accidents” and “Studies.”

Engines Keep Secrets
Downloading your engine’s ECM can help explain what happened in a wreck

Accident reconstructionists must constantly remain aware that the electronic control module is not a magic box. The tractor’s so-called “black box” can supply comprehensive data about a tractor’s hardware and operating set-up at the time of a wreck, but that is not enough.

“It helps. It helps a whole lot sometimes, “says Beaver, “but it is only part of the puzzle. You cannot rely on it alone.

ECMs were designed to get the most out of an engine by giving owners ways to maximize performance. They measure and record all sorts of data, from injector performance and timing to comparative cylinder efficiencies. But some of the data they record is also crucial to accident investigation.

What a particular engine’s ECM can tell reconstructionists will not be the same in every case. Different OEMs set up their ECMs differently, and different models from manufacturers may also record different data. Owners may also decide not to use the full range of potential ECM functions and restrict the device to basics.

A Detroit Diesel ECM is capable of telling us, second by second:

  • Vehicle speed in mph.
  • Engine speed in rpm.
  • Brake: In use or not. Technically a record of pedal position.
  • Clutch: Engaged or not. Technically a record of pedal position.
  • Engine load in percentage terms. Technically the ratio of actual engine torque divided by max torque.
  • Throttle in percentage-of-use terms. Technically a measure of pedal position.
  • Cruise control: on or off.
  • Last stop record: Triggered when the vehicle speed changes from being driven (at least 1.5 mph with engine rpm greater than zero for two seconds) to stop, which means less than 1.5 mph. The last stop record contains vehicle and engine operating data for one minute and 45 seconds before and 15 seconds after the last stop trigger point.
  • Hard brake data: Triggered when vehicle wheel speed decelerates more than 7 mph per second (the actual mph number can be set by the owner). Records engine operating data for one minute before and 15 seconds after event in one-second intervals.
  • Diagnostic code: Active or inactive (if active all other engine properties measures set for the ECM will be recorded).

Beaver cites an example of an ECM backing up a trucker’s story. “A woman careened her car across a median and into a ditch on the other side of the carriageway at night. She got out of the wreckage and found her way back to her original side of the interstate, where a trucker struck her as he rolled by. He said he never saw her but felt something hit, a deer in all likelihood. So he stopped. He saw some damage but no sign of blood, hair or clothing, so he drove on. Police wanted to charge him with leaving the scene of an accident, but his engine’s ECM shows he did stop at the time of the impact.”

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