What Is a Black Box in a Car? How to Preserve Evidence After an Accident

You were hurt in a crash, and someone has mentioned the car’s “black box.” It’s the event data recorder (EDR), which saves a few seconds of data around a crash, such as speed, braking and whether the driver was buckled. No federal rule requires one, but the National Highway Traffic Safety Administration (NHTSA) estimates that 99.5% of model year 2021 cars and other vehicles up to 8,500 pounds had one. The data belongs to the car’s owner, or the lessee if it’s leased, and like store video and skid marks, it can disappear within days. If the other driver’s insurer is already calling and evidence is the last thing on your mind, that’s normal. To preserve the evidence, keep the car from being repaired or scrapped until its data is read, and ask for video and other records in writing right away.

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What is a black box in a car?

A car’s black box is its event data recorder: a device or function that records the car’s speed and other data just before and during a crash, so it can be retrieved afterward. It doesn’t record audio or video, and it saves data only when a crash or a similar jolt sets it off (49 CFR 563.5, 563.11).

The trigger is a change in speed of at least 8 km/h (about 5 mph) within 0.15 seconds, or an air bag deployment (49 CFR 563.5). The owner’s manual must say that it records data “for a short period of time, typically 30 seconds or less,” and that it records no personal data, such as your name, age or the crash location (49 CFR 563.11).

Do all cars have a black box?

No, not every car has one. Federal rules don’t require an event data recorder, but NHTSA estimates that 99.5% of model year 2021 cars and other vehicles up to 8,500 pounds had one.

If a car or other vehicle up to 8,500 pounds built since September 2012 has an EDR, it must record speed, accelerator and brake use in the 5 seconds before a crash (49 CFR 563.3, 563.7). Older cars may have a recorder that didn’t have to meet that rule: NHTSA estimated in 2012 that about 92% of model year 2010 light vehicles had some EDR capability (89 FR 102810). Heavy trucks aren’t covered (see below).

What does a car’s black box record, and for how long?

It records a short window around the crash: speed, accelerator and brake use for the 5 seconds before it, plus the driver’s seat belt status, how sharply the car’s speed changed and when the front air bags deployed. Saved data stays in memory even when the power is cut, but data from a crash that didn’t set off an air bag can be overwritten by a later crash (49 CFR 563.5, 563.9).

Source: 49 CFR 563.7.

NHTSA has found that 5 seconds captures only a small part of the time a vehicle spends approaching and crossing an intersection, and it is phasing in 20 seconds for vehicles built from September 1, 2028 (49 CFR 563.7; 91 FR 28432).

See how the data figures in rear-end crashes, T-bone crashes at intersections and head-on collisions.

Who owns a car’s black box data, and who can get it?

The data belongs to the vehicle’s owner or lessee, and anyone else generally needs the owner’s or lessee’s consent or a court’s authorization (Driver Privacy Act of 2015). So getting the other car’s data usually takes its owner’s consent or a court order.

Anyone else may access it only if:

• a court or other judicial or administrative authority authorizes it;
• the owner or lessee consents in writing, electronically or by recorded audio, including through a subscription that describes how the data will be retrieved and used;
• it’s retrieved in certain federal safety investigations, such as the National Transportation Safety Board’s, with limits on disclosing the owner’s identity and the vehicle identification number (VIN);
• it’s retrieved for emergency medical response after a crash; or
• it’s retrieved for traffic safety research that doesn’t disclose the owner’s personal information or the VIN.

Reading the data takes special equipment and access to the vehicle or the recorder (49 CFR 563.11), and carmakers must make a retrieval tool commercially available (49 CFR 563.12). Before you consent to anyone reading your own car’s data, ask what it’s for.

How do you preserve a car’s black box data?

After a crash that hurt someone, keep your car from being repaired, sold or scrapped until you’ve asked a lawyer whether its recorder should be read, and ask the other driver’s insurer in writing to hold the other car too. The recorder goes wherever the car goes: a body shop, a salvage auction or the crusher.

• Find the car and whoever has it: a tow yard, a body shop or your insurer. Tell them in writing that it may be evidence and shouldn’t be repaired, sold, crushed or stripped yet.
• Don’t sign the title over after a total loss until you’ve asked about the recorder.
• Move quickly if the air bags didn’t go off, since that crash’s data can be overwritten by a later one (49 CFR 563.9).
• Inspect together, in a way the other side can attend. Taking parts off can destroy evidence too, as a Michigan case below shows.

Do semi trucks have black boxes?

Not under the federal EDR rule, which covers only vehicles rated at 8,500 pounds or less (49 CFR 563.3). But trucking companies covered by federal hours-of-service rules generally must have drivers log their hours on an electronic logging device (ELD), and those logs only have to be kept for 6 months (49 CFR 395.8).

An ELD is an electronic logbook: it tracks driving hours, not the seconds before a crash. It automatically records the date, time, location, engine hours, miles and the driver, truck and carrier when the driver’s duty status changes, when the engine starts or shuts off, and at least hourly while the truck is moving (49 CFR 395.26).

Carriers must keep drivers’ logs and supporting documents, and a backup copy of ELD records, for 6 months (49 CFR 395.8(k), 395.22(i)). Photograph both sides of the truck: trucks covered by the federal rules generally must show the carrier’s name and USDOT number there (49 CFR 390.21T). For the other records a trucking company keeps, see how a truck crash differs from a car crash.

What other evidence disappears after a crash?

Video gets recorded over, road marks fade, cars get repaired or scrapped, and witnesses get harder to find. Here’s what to save, and how:

If the other driver fled, nearby video and anything the car left behind matter even more; see what to do after a hit-and-run.

What about phone records?

Phone records can show whether a driver was on a call or texting when the crash happened. Once a lawsuit is filed, each side can request relevant records through discovery, the formal exchange of evidence, and a subpoena can require someone outside the case, such as a phone carrier, to produce documents (Federal Rules of Civil Procedure 26(b)(1) and 45; in Michigan, MCR 2.302(B)(1) and 2.305). Keep your own photos, videos and messages, and ask a lawyer before deleting any post.

Isn’t the police report enough?

No. The report records what the officer saw and concluded and points to other evidence, but the officer’s view of fault is an opinion, not a final ruling.

What is a preservation letter?

A preservation letter is a written request, usually sent by a lawyer, telling someone that a claim is coming and asking them to keep specific evidence. It isn’t a court order, but it puts the recipient on notice that the evidence matters. (Losing or destroying evidence is called spoliation, so it’s also called a spoliation letter.)

It can go to the other driver’s insurer (the car and its recorder), a trucking company (the truck, ELD records and dispatch records), a business with a camera, a tow yard, or your own insurer if it’s about to take your totaled car. A useful letter names the crash’s date, time and place and exactly what to keep, and asks that nothing be repaired, altered or destroyed before an inspection both sides can attend.

Notice matters because courts can penalize a party that loses evidence it should have kept once a claim was expected (see below), and a clear letter makes it hard to say later that no one knew the evidence mattered.

Worried the evidence won't be there when you need it? Get a free case review. Four quick questions, no cost, no obligation.

What is spoliation, and what can a court do about it?

Spoliation means losing, destroying or failing to preserve evidence that matters to a case. Courts can respond in proportion to the harm, from letting the jury assume the missing evidence would have hurt the side that lost it to, in serious cases, dismissing the claim.

In federal court, losing electronic information that should have been kept can lead to measures to cure the harm, and, if the party meant to deprive the other side of it, to a presumption that it was unfavorable or the end of the case (Federal Rule of Civil Procedure 37(e)). State courts have their own rules.

Can lost evidence hurt your own claim?

Yes. The duty to keep evidence applies to the injured person, too.

So keep your car and messages, and give the other side notice before anything is taken apart.

What to do next

1. Get medical care, and keep every record. Our checklist of 10 things to do after a car accident covers the first days.
2. Save what’s yours today: photos, dashcam files, texts, witnesses’ names and numbers, and anything damaged in the crash, such as a helmet or a child’s car seat.
3. Ask for video in writing now from nearby businesses, homes and transit agencies, naming the camera and the time window.
4. Hold the car. Don’t let it be repaired, sold, scrapped or signed over until you’ve asked whether its recorder should be read. If a truck was involved, its logs only have to be kept for 6 months.
5. Get a free case review. Tell us what happened in four quick questions, at no cost. A lawyer can send preservation letters to anyone holding evidence. In Michigan, you can also compare injury lawyers near you.

What waiting can cost

• The recorder’s data. It goes wherever the car goes, and some of it can be overwritten by a later crash (49 CFR 563.9).
• The video. Footage gets recorded over.
• The truck’s records. Driver logs and ELD backups only have to be kept for 6 months (49 CFR 395.8(k), 395.22(i)).
• Your own claim. Evidence you could have kept can be held against you (in Michigan, Brenner v Kolk).

What a good outcome looks like

The car’s data is read in a way both sides can check, and the video, vehicles and records are saved before anyone can lose them. Fault is decided on what happened, not on whose memory sounds better. From hoping the other driver’s story falls apart to proving what happened with the car’s own data, the video and the vehicles.

For more, see our car accident lawsuit guide or browse all car, truck and motorcycle accident guides.

Updated September 25, 2026

This guide is general information, not legal advice, and laws change. For advice about your situation, talk to a lawyer licensed in your state. Reading this page or contacting us does not create an attorney-client relationship.