Your Car's Black Box: Event Data Recorders and Why a Preservation Letter Goes Out First

Published March 10, 2020 · Injury Law Basics

The other driver says he was doing the speed limit and braked hard. You say he never slowed down. There were no independent witnesses, the intersection has no camera, and the police report records both versions without picking one. In many crashes, the most objective witness to what happened is sitting inside the other driver's car, and almost nobody thinks to ask it.

That witness is the event data recorder, the "black box" built into most modern passenger vehicles. Used well, it can settle a fault dispute with hard numbers. Ignored for a few weeks, it can end up crushed at a salvage yard.

What an event data recorder is

An event data recorder, or EDR, is a function of the computer that controls a vehicle's airbags. It constantly monitors the vehicle's sensors, and when it detects a crash, or a sudden change in speed that might be one, it saves a short snapshot of what the vehicle was doing.

Federal law does not require automakers to install EDRs, but most do, and the ones that do must follow a federal regulation, 49 C.F.R. Part 563. That rule applies to passenger cars, SUVs, pickups, and vans built on or after September 1, 2012 that are equipped with an EDR. Many older vehicles have recorders too; what they capture simply varies more by manufacturer.

What the data shows

For covered vehicles, Part 563 requires the recorder to capture a standard set of data elements. The most important for a fault dispute are recorded for the five seconds before the crash, sampled twice per second:

• Vehicle speed, as the car's own systems measured it
• Accelerator position, showing whether the driver was on the gas
• Service brake on or off, showing whether and when the driver braked

The recorder also captures the driver's seat-belt status, how sharply the vehicle's speed changed in the impact (called "delta-V"), and when the airbags deployed. If the vehicle's systems record them, the EDR may also save steering input, anti-lock brake and stability-control activity, engine RPM, and the front passenger's seat-belt status.

Put together, those five seconds can answer the questions that decide most crashes. Was the other driver speeding? Did he brake at all? Did he accelerate to beat a yellow light? How hard was the impact, which matters when an insurer claims a crash was too minor to hurt anyone?

Who owns the data

Under a federal law passed in 2015, the Driver Privacy Act, the data in an EDR is the property of the vehicle's owner, or the lessee if the vehicle is leased. That is why we cannot simply walk up to the other driver's car with a laptop. Access usually comes through the owner's consent or, once a lawsuit is filed, through the court.

Your own car's data belongs to you, and it can help you as well. If you were stopped, or traveling at a safe speed and braking, your recorder can prove it.

How the data is retrieved

The data is downloaded with specialized retrieval equipment, usually connected to the vehicle's diagnostic port or directly to the airbag control module. The download should be done by a trained crash reconstructionist who documents each step, so the report holds up in court. The raw report is technical; part of the reconstructionist's job is to explain it, and to compare it to the physical evidence: crush damage, skid and yaw marks, final rest positions, and the scene measurements in the police report.

The data has limits. Recorded speed can be thrown off by wheel slip or locked brakes, and the recorder knows nothing about the other vehicle. That is why EDR data works best alongside other proof: the crash report, witness statements, and video from a dash camera or a nearby business.

Why weeks matter

Here is the problem. When an insurer declares a car a total loss, it takes ownership, moves it to a salvage auction, and sells it. The buyer may part it out or crush it. That can happen within a few weeks of the crash, long before most injured people have thought about evidence, and when the car goes, the airbag module goes with it.

Even a car that survives can lose data. Part 563 requires the recorder to lock the data from a crash that deploys the frontal or side airbags so it cannot be overwritten. A crash that does not deploy the airbags is treated differently: that data can be overwritten by later events, including later driving if the car is repaired and put back on the road.

The preservation letter

That is why a preservation letter is one of the first things our office sends in a serious crash case. Sometimes called a spoliation letter, it is a formal written demand that the evidence be kept intact. It goes to the other driver, the other driver's insurer, the tow yard holding the vehicle, and, if the car has already moved, the salvage auction. It identifies the vehicle by VIN, states that litigation is likely, and asks that the vehicle and its airbag control module not be sold, crushed, repaired, or downloaded without notice.

The letter matters legally as well as practically. Ohio recognizes a separate claim for willful destruction of evidence. In Smith v. Howard Johnson Co., 1993-Ohio-229, the Supreme Court of Ohio held that the claim requires, among other things, that the defendant knew litigation was pending or probable and willfully destroyed evidence designed to disrupt the case. A preservation letter establishes that knowledge. I discussed the limits of that claim in an earlier post on destroyed evidence; the lesson is that preserving evidence beats suing over its loss.

Commercial trucks carry their own recorders, along with electronic logs and telematics, and the stakes are higher. I covered that in last year's post on electronic logging devices.

What this means for you

• If you were seriously hurt and fault is disputed, ask early where the other vehicle is and whether it has been declared a total loss.
• Do not let your own car be sold or salvaged before someone decides whether its data matters. Tell your insurer in writing that you want it held.
• Keep the tow receipt, the claim numbers, and any letters about the vehicle's status.
• Read our guide chapter on gathering evidence while it still exists for the other evidence that disappears on a similar timetable.

You can learn more about how we handle serious crash cases on our Dayton car accident lawyer page.