Trucking Accident Evidence: What Disappears and When

A semi-truck just caused a catastrophic accident. The driver was speeding. He'd been on the road for 14 hours. The company knew the brakes needed work but kept the truck running anyway. All of that is provable—if you get the evidence before it's gone.

That's the challenge in trucking cases. The most valuable evidence has the shortest lifespan. Understanding what exists, where it lives, and how fast it disappears is the difference between proving what happened and being left with nothing but competing stories.

The Evidence That Matters

Electronic Control Module (ECM) / Event Data Recorder (EDR)

Modern commercial trucks contain electronic systems that record operational data—speed, throttle position, braking, engine RPM, cruise control status, and more. Some systems capture data continuously; others record only when triggered by an event like hard braking or a collision.

The critical limitation: ECM data gets overwritten. The storage is finite. As the truck continues operating, new data writes over old data. Depending on the system and how the truck is used, you may have 30 days. You may have less.

If the truck is repaired and returned to service quickly, the data that proves what happened in the moments before the crash may be gone before anyone thinks to preserve it.

Driver Logs and Hours of Service Records

Federal regulations limit how long commercial drivers can operate. Violations—driving beyond the allowed hours, inadequate rest breaks—are common factors in fatigue-related crashes.

Electronic logging devices (ELDs) are now required for most commercial trucks, making falsification harder than it was with paper logs. But the data still has retention limits. Motor carriers must retain ELD records for six months, but that's the regulatory minimum. Companies may not voluntarily preserve records beyond what's required, especially if those records show violations.

Dispatch and Communication Records

Text messages, dispatch instructions, GPS tracking, and internal communications can show:

• Whether the driver was pressured to meet unrealistic schedules
• Whether the company knew about safety issues
• What instructions the driver was given before the accident

These records exist on company servers, in dispatch systems, and on personal devices. They can be deleted, overwritten, or "lost" remarkably quickly once the company realizes litigation is coming.

Maintenance Records

Was the truck properly maintained? Were there known mechanical issues? Brake problems, tire wear, steering defects—these don't happen overnight. The maintenance history tells the story.

Companies are required to keep maintenance records for the vehicle and for one year after the vehicle leaves their control. But required and available aren't always the same thing.

Physical Evidence

The truck itself is evidence. Damage patterns, mechanical condition, tire wear, brake measurements—all of this can be examined by experts. But only if the truck is preserved.

If the truck is repaired, sold, or scrapped, that evidence is gone. Trucking companies have financial incentives to get damaged vehicles back on the road quickly. Waiting means lost revenue.

The Preservation Timeline

Here's the reality of how fast evidence disappears:

Evidence Type	Typical Preservation Window
ECM/EDR data	30 days or less (overwrites with use)
Scene evidence	Hours to days (weather, cleanup, repairs)
Physical vehicle condition	Days to weeks (repair or disposal)
Witness memory	Weeks (fades quickly)
ELD/driver logs	6 months (regulatory minimum)
Dispatch records	Varies (no guaranteed retention)
Maintenance records	1 year (regulatory minimum)

The most critical evidence—ECM data and scene evidence—has the shortest lifespan. By the time most people think about preservation, it may already be too late.

The Spoliation Letter

A spoliation letter is a formal written demand to preserve evidence. It puts the trucking company, driver, and any relevant parties on notice that litigation may follow and that they have a legal duty to preserve relevant evidence.

Once a party receives a spoliation letter (or reasonably anticipates litigation), they cannot destroy, alter, or lose relevant evidence without legal consequences. Courts can impose sanctions, allow adverse inference instructions (telling the jury they can assume the destroyed evidence was unfavorable), or even dismiss defenses.

The spoliation letter should go out immediately. Not next week. Not after you've had time to think about it. The day of the accident or the day after.

An effective spoliation letter specifically identifies:

• The accident (date, location, parties)
• The evidence to be preserved (ECM data, logs, communications, maintenance records, the vehicle itself)
• The legal obligation to preserve
• The consequences of spoliation

What to Preserve and How

Immediate (Day 1)

Scene documentation. Photographs and video from every angle. Damage to all vehicles. Road conditions. Skid marks. Traffic control devices. Weather. Get as much as possible before the scene is cleared.

Witness information. Names, phone numbers, what they saw. Witnesses scatter quickly.

Your own records. If you were injured, photograph your injuries. Keep a journal of symptoms and treatment.

Within 48-72 Hours

Spoliation letter. This is attorney work. A properly drafted letter goes to the trucking company, the driver, and potentially the insurer. It creates a legal duty to preserve.

Police report request. Get the report number at the scene; request the full report as soon as it's available.

Medical records. Begin documenting your injuries and treatment.

Within 30 Days

ECM data extraction. If a spoliation letter is in place, the company should preserve the data. But verification matters. In some cases, independent extraction is necessary to ensure the data is actually preserved.

Vehicle inspection. If the truck hasn't been repaired or disposed of, a defense expert should examine it.

Subpoena preparation. For ELD data, dispatch records, maintenance files, and driver qualification files.

When Companies Destroy Evidence

It happens. Despite legal obligations, records go missing. ECM data gets overwritten because the truck went back into service. Phones get wiped. Servers get "upgraded."

When spoliation occurs, there are remedies:

• Adverse inference instructions tell the jury they may assume the destroyed evidence was unfavorable to the party who destroyed it.
• Sanctions can include monetary penalties or limitation of defenses.
• Separate claims for spoliation may be available in some circumstances.

But remedies aren't as good as having the actual evidence. An adverse inference helps, but it doesn't replace ECM data showing the driver was doing 80 in a 55 zone.

Why Speed Matters

Trucking companies have lawyers on call. When a serious accident happens, that call goes out fast. Their focus is protecting the company, which often means controlling the narrative around evidence before plaintiffs have a chance to preserve it.

Victims who wait—who think they have time to figure things out, who don't realize how quickly evidence disappears—lose that race. By the time they hire a lawyer, the truck is repaired, the ECM is overwritten, and the case becomes an uphill battle.

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Trucking accident cases are won or lost in the first days after the crash. The evidence that proves what really happened exists—but it doesn't exist for long. Preservation isn't optional; it's the foundation of everything that follows.

At Addison Law, we handle trucking accident cases throughout Oklahoma. If you or a family member was seriously injured in a crash involving a commercial truck, contact us immediately. Evidence preservation is our first priority.

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This article is for general information only and is not legal advice.