You’re wondering whether what you recorded, or what got recorded automatically, is actually useful. Maybe you have a dashcam and you’re not sure if it captured the right moment. Maybe someone at the scene took out their phone. Maybe you’ve heard something about a black box in the car and you don’t know if that applies to your situation. You’re asking the right questions, and the answers matter more right now than they will at any other point in this process, because several types of evidence from your accident are being lost or overwritten while you’re reading this.

That’s not a scare tactic. It’s the one thing about accident evidence that almost nobody understands until it’s too late, so it’s worth starting there before anything else.

Modern vehicles contain an Event Data Recorder, commonly called an EDR or, in the language of news coverage and legal proceedings, a black box. Nearly every passenger vehicle manufactured after 2013 has one, and most vehicles made after 2008 have some version of the technology. What the EDR captures varies by manufacturer, but it typically records vehicle speed in the seconds before a crash, brake application, throttle position, steering input, seatbelt status, and whether airbags deployed. In other words, it records exactly what the vehicles were doing in the moments that determine fault. That data exists right now, in both cars involved in your accident, waiting to be downloaded.

Here is what nobody tells you: that data does not wait forever. EDRs record on a loop. In many vehicles, the data from a crash is preserved temporarily but can be overwritten if the vehicle is started and driven again before the data is downloaded. Some systems preserve crash data more reliably than others, but you cannot know which type is in the other driver’s car, and you should assume the worst. Once that data is gone, it is gone. There is no recovery. The physical device will still exist but the recorded event will have been replaced by more recent driving data.

The way you stop that from happening is through a spoliation letter, sometimes called a preservation letter or evidence preservation demand. This is a formal written notice sent to the other driver, their insurance company, and in some cases their vehicle’s manufacturer, demanding that all data, including EDR data, be preserved and not destroyed, overwritten, or tampered with. The legal significance of this letter is substantial. Once a party receives notice that evidence is relevant to potential litigation and destroys it anyway, a court can instruct a jury to assume that the destroyed evidence would have been unfavorable to the person who destroyed it. That instruction is called an adverse inference, and it can be decisive. A spoliation letter shifts the legal and practical burden of evidence preservation onto the other side in a documented way. An attorney can send this within hours of being retained. It is one of the most concrete and time-sensitive things a personal injury lawyer does in the early stage of a case, and it is one of the clearest reasons not to wait weeks before making a call.

The EDR in your own vehicle is also worth understanding. That data belongs to you as the vehicle owner under federal law, specifically under the provisions that were formalized when the National Highway Traffic Safety Administration standardized EDR requirements. But accessing it isn’t simple. The data requires proprietary software to download, software that is typically owned by the vehicle manufacturer and used by authorized crash reconstruction specialists. Your attorney can arrange for that download, but it needs to happen before your car is repaired, sold, or totaled out. If your car has already been declared a total loss and sent to a salvage yard, the window to retrieve that data may be closing right now.

Dashcam footage is the evidence type people are most aware of and most likely to have, and it has a preservation problem of its own that is different from the EDR issue but just as urgent. Most dashcams record on a continuous loop, overwriting the oldest footage as the card fills. Some cameras have a collision detection feature that automatically locks the clip around an impact event so it isn’t overwritten. If your camera has that feature and it triggered, you may be fine. If it didn’t trigger automatically, or if you’re not certain, remove the memory card from the camera right now, before you drive the car again, before the card fills, and before anything else. Do not copy the footage and delete the card. Keep the original card. Make copies from it, but the original file on the original card contains metadata that a forensic examiner can use to verify the footage is unaltered, which matters if the other side challenges its authenticity.

Dashcam footage from your own camera is obviously useful if it shows the other driver’s actions before the collision. But the metadata embedded in that file is something even most attorneys don’t immediately think about exploiting. Every video file contains technical data about when it was recorded, the device that recorded it, and in many cases GPS coordinates and speed data if the camera has those capabilities. That embedded information can corroborate or contradict claims about where the accident occurred, what time it happened, and how fast each vehicle was traveling. A forensic analysis of dashcam metadata has resolved disputed liability cases where the raw video itself was ambiguous.

Bystander phone video is a different category with its own set of considerations. If someone at the scene told you they got the accident on their phone, get their contact information before they leave. This is harder than it sounds in the shock of an accident scene, but it may be the most important ten seconds you spend there. A bystander has no obligation to preserve that footage, hand it over to you, or respond to your calls later. If you have their contact information and you or your attorney reach out quickly, many people will cooperate. If you don’t have their information, that footage may disappear with them. In some cases, attorneys can issue a legal hold notice to a bystander if their identity and contact information are known. Without that information, there is no mechanism to compel preservation before litigation is filed.

Your own phone may contain evidence you haven’t considered. If you had navigation running, many mapping applications log your route and speed in real time. Google Maps, Apple Maps, and Waze all maintain location history that can be retrieved and used to establish your speed and position at the time of the accident. This data cuts both ways, which is worth being honest with yourself about. If you were driving within the speed limit and following the route you described, that data supports your account. If you were speeding or in a place you said you weren’t, the data will reflect that too. The same principle applies to the other driver’s phone. Phone location and speed data can be subpoenaed in litigation, and in cases where one driver claims they were traveling slowly or weren’t at a particular location, that data has produced decisive contradictions.

Traffic camera footage is the evidence type with the shortest preservation window of all, and it’s the one most people don’t think to pursue until it’s gone. Municipalities, businesses, and transportation departments maintain camera footage on loops that are frequently overwritten within 24 to 72 hours. If your accident occurred at an intersection with a traffic signal camera, near a business with exterior security cameras, or in an area with municipal surveillance coverage, that footage exists right now and will be destroyed on a routine schedule regardless of your accident. Your attorney can send preservation demands to the relevant parties, or in some cases physically go to a business and request that they hold the footage. But this has to happen within the first day or two. There is no reliable way to recover this footage once it has been overwritten, and there is no legal mechanism to compel its preservation retroactively once it’s gone.

Social media is an evidence category that works against you more often than it helps you, and it’s worth addressing directly. The at-fault driver’s social media is fair game in discovery. Posts, check-ins, stories, and photos timestamped around the time of the accident have been used to establish distraction, intoxication, and inattention. Your own social media is equally fair game. Insurance companies and defense attorneys routinely monitor the social media accounts of claimants during the claims process and throughout litigation. A photo of you standing at a family gathering two weeks after an accident that you claimed left you bedridden will be used against you regardless of context. This is not a reason to delete anything, because deletion of potentially relevant material after a claim has been initiated can itself be characterized as spoliation. It is a reason to stop posting about your physical activities, your mood, your recovery, or anything related to the accident until the claim is resolved.

The broader principle that connects all of this is that the first 48 to 72 hours after a car accident is a period of evidence that will never come back. The EDR data is most reliably intact. The dashcam card hasn’t been overwritten. The traffic camera footage still exists. Bystanders are still reachable. The accident scene still reflects the physical reality of the crash. Every day that passes without action is a day that some category of evidence becomes less available, less reliable, or entirely gone. Insurance companies understand this timeline. Their adjusters call quickly not just to get your statement but because they know that claimants who don’t move quickly often lose evidence that would have helped them.

An attorney who handles car accident cases can initiate evidence preservation across all of these categories within hours of being retained. Most personal injury attorneys take these cases on contingency, meaning no fee unless they recover money for you. The cost of waiting is not financial. The cost of waiting is measured in overwritten black box data, erased camera loops, and footage that disappeared with a stranger’s phone.

This content is provided for general informational purposes only and does not constitute legal advice. It does not create an attorney-client relationship. The preservation timelines and legal standards described may vary depending on the specific facts of your situation and the jurisdiction in which your accident occurred. If you have been injured in a car accident, consult with a licensed personal injury attorney as soon as possible.