Just 23 minutes after dropping off her two young children, Gail Palmgren drove along East Brow Road in her 2010 crimson Jeep Rubicon.
The sun was shining and the skies were clear on April 30 as the vehicle went off the road onto a small grassy area and struck a tire-size boulder weighing about 435 pounds. The Jeep went airborne and overturned, the rear crashing on one bluff, then another, falling a total of about 350 feet. The vehicle lay in a wooded area at the base of Walden's Ridge above the W Road for about seven months before it was discovered.
Now Hamilton County Sheriff's Office investigators have examined the Jeep wreckage and used the vehicle's black box to try to learn why Palmgren, 43, drove over the edge.
Investigators said Palmgren was not wearing her seat belt when the Jeep crashed. They have declined so far to release other findings from the box.
Hamilton County Sheriff Jim Hammond said he has seen preliminary reports from the traffic unit and the medical examiner's office in Knoxville, where Palmgren's remains were examined by a forensic anthropological team.
Pending the issue of final reports, Hammond said, it appears to be "just a terrible accident."
Inside the box
The National Highway Traffic Safety Administration estimates that 85 percent of cars on the road have the boxes, also known as event data recorders, whose information can be retrieved and examined after a crash.
The black boxes, which often are actually aluminum in color, record data including speed, seat belt use, braking and acceleration.
"Not all cars have them. Really, from 2001 forward to where we are now, most heavy manufacturers are putting them in there," said Chattanooga Police Sgt. Chad Sullivan, who works in the special operations division and investigates DUIs. Mark Kimsey, traffic sergeant with the Hamilton County Sheriff's Office, declined to be interviewed because he is working on the Palmgren case.
Traffic investigators get subpoenas to gain access to the boxes in some cases if there is a fatality or serious injury in a crash.
Chattanooga has had 17 traffic fatalities so far this year and investigators retrieved data from one black box. In several cases, investigators didn't have the software to retrieve the data or were unable to access the data.
Auto manufacturers began installing the recorders in vehicles about 10 years ago, but are not required to do so.
An event such as a collision or heavy braking will trigger the box to record.
"It will record from that point forward," Sullivan said. "Some of them really are detailed. They'll tell what the temperature setting was on the A/C unit. That falls back to the manufacturer and how much info they want to release."
Under federal requirements, the boxes must record 15 types of crash data. There are federal standards for an additional 30 types of data.
Palmgren's Jeep was a newer model that records a wealth of information compared with earlier versions of the recorder, said Michael Palese, a spokesman for Jeep. Before the 2010 model, if an airbag did not inflate, the data may not have recorded.
"Up until a year or so ago, if there was an accident [without airbags deploying], there was nothing you would be able to capture from it," Palese said. "Now, I think there are delta-V's [changes in velocity], crash forces, that will trigger the capturing of some of the things that happened during a crash event. If it was an extreme impact that had a certain delta-V it would cause a reading to be taken."
The model in Palmgren's Jeep stores data for five seconds before a crash at 100 millisecond intervals. Some of the measurements include engine RPMs, vehicle speed, engine throttle percentage, accelerator pedal percentage, anti-lock brake system and steering input.
The model also measures the yaw rate, or velocity measured from side to side.
"You would know those directional forces that the passengers were experiencing during the course of an accident," Palese said.
No final answers
Despite the detail some boxes capture, the technology cannot provide answers to everything.
"The biggest help we get from it is when it fills in a void," Sullivan said.
"If we get people who are ejected from a vehicle, it will help us learn whether or not they were wearing their seat belt or not. ... but it's not going to tell you why the person turned left or right. It's not going to tell you if they were intoxicated."
Some groups have criticized the widespread installation of black boxes, citing privacy concerns.
"There is good reason to believe that the promotion of universal black box installation in new vehicles has more to do with regulatory, enforcement, judicial and corporate economic interests; all at the expense of vehicle owners who are forced to pay for and retain this form of self-surveillance," reads a statement from the National Motorists Association on the organization's website.
Many drivers don't know their vehicles are equipped with the boxes. The National Highway Transportation Safety Administration states manufacturers must notify owners of the boxes. Auto companies notify owners by printing information in the owner's manual.
"We didn't ask they [black boxes] get put in there, but we are glad they are in there," Sullivan said.
"If the shoe was on the other foot and they [critics] were the victim, they would probably be glad it's in there," Sullivan said.