TL;DR: A truck accident investigation examines far more than a car crash: electronic logging device records, engine and event data, maintenance files, the driver’s qualification file, and post-crash drug and alcohol tests. Federal rules let trucking companies discard some of these records within months, which is why the evidence needs to be preserved quickly.
Within hours of a serious truck crash, the trucking company often knows more about what happened than you do. Many carriers and their insurers send their own people to the scene quickly. They photograph the trucks, talk to the driver, and start building a version of events. Meanwhile, you may still be in the emergency room.
A truck accident investigation is a race over evidence. The records that show what really happened, from the driver’s hours to the truck’s brakes, are held by the trucking company, and federal law only requires some of them to be kept for a short time.
Who Investigates a Truck Crash in California
Police and the CHP
Local police or the California Highway Patrol respond to the scene, document it, and write a collision report. For major collisions, the CHP has a specialized unit: the Multidisciplinary Accident Investigation Team, or MAIT. California has eight MAIT teams, including one in the Southern Division based in Los Angeles. Each team is made up of a CHP sergeant, two or more officers, a Motor Carrier Specialist, and a senior transportation engineer from Caltrans, and it analyzes the human, vehicle, and environmental factors before, during, and after the crash.
The trucking company and its insurer
The carrier and its insurer usually run their own investigation. Their goal is to limit the company’s exposure, and they control most of the key records.
Your attorney
An attorney representing the injured person conducts an independent investigation: sending preservation demands, hiring reconstruction experts, and obtaining the company’s records through formal discovery.
Evidence a Truck Accident Investigation Collects
Scene evidence
Photos and video of the vehicles, skid marks, debris, road conditions, signals, and sight lines; witness statements; and the police or CHP report. Nearby business and traffic cameras may record over footage quickly.
Engine and event data recorder information
Many commercial trucks have an engine control module or event data recorder, often called the black box, that can capture information such as speed, braking, and throttle around the time of a crash. This data can be overwritten, which is why it needs to be preserved early. The black box is not the record of the driver’s hours. That comes from the logging device.
Electronic logging device and hours-of-service records
Under 49 CFR 395.8, most interstate commercial drivers have been required to record their duty status on an electronic logging device since December 18, 2017, with limited exceptions. These records show how long the driver had been on duty and driving, which is central to any fatigue claim. The FMCSA explains the ELD rule and who it covers.
Maintenance and inspection files
Brake, tire, and lighting defects cause serious crashes. Inspection and maintenance records show whether the carrier kept the truck in safe condition.
The driver qualification file
Under 49 CFR 391.51, carriers must keep a driver qualification file, including the driver’s application, motor vehicle record, road test or equivalent, and medical examiner’s certificate.
Post-crash drug and alcohol tests
Under 49 CFR 382.303, a carrier must test a commercial driver after a crash that causes a death. It must also test when the driver receives a citation for a moving violation and the crash involved an injury treated away from the scene or a vehicle that had to be towed. Alcohol tests should happen within 2 hours and may not be attempted after 8 hours. Drug tests must happen within 32 hours.
How Long Trucking Companies Must Keep Records
This is where speed matters most. Federal rules set minimum retention periods, and some are short:
| Record | Minimum federal retention | Rule |
|---|---|---|
| Records of duty status and supporting documents | 6 months | 49 CFR 395.8(k) |
| Maintenance and inspection records | 1 year, plus 6 months after the vehicle leaves the carrier’s control | 49 CFR 396.3(c) |
| Accident register | 3 years | 49 CFR 390.15 |
| Driver qualification file | Length of employment plus 3 years | 49 CFR 391.51 |
| Positive drug results and alcohol results of 0.02 or higher | 5 years | 49 CFR 382.401 |
| Negative drug and alcohol results | 1 year | 49 CFR 382.401 |
No federal rule sets a retention period for black box data, and it can be overwritten as the truck keeps operating. A six-month clock on driver logs means a case that waits too long can lose the single most important record of driver fatigue.
Preservation Letters and Destroyed Evidence
A preservation letter, sometimes called a litigation hold letter, formally notifies the trucking company and its insurer that a claim is coming and that they must keep all relevant evidence: the truck, its electronic data, logs, maintenance records, dispatch communications, and video. It is usually one of the first things a truck accident attorney sends.
When evidence is destroyed after a company knew it would matter, that is called spoliation. California juries can be instructed under CACI 204 that if a party willfully suppressed evidence, they may conclude the evidence would have been unfavorable to that party. Sending the preservation letter early makes it much harder for a company to claim it did not know.
Proving Trucking Company Negligence
The investigation often reveals more than one cause. Beyond the driver’s own mistakes, the evidence can show company-level failures:
- Pushing drivers past hours-of-service limits to meet delivery schedules
- Hiring or keeping drivers with poor safety records
- Skipping inspections or deferring brake and tire repairs
- Loading cargo unsafely or exceeding weight limits
Those findings can bring the carrier, a maintenance contractor, a cargo loader, or a parts manufacturer into the case. Our guide to FMCSA regulations for truck accidents covers the safety rules investigators check against.
California deadlines still apply while the investigation is underway. Most injury lawsuits must be filed within two years under Code of Civil Procedure 335.1, and claims against a public agency need a government claim within six months under Government Code 911.2.
Final Thoughts
Being hit by an 80,000-pound truck is terrifying, and the aftermath can feel like a fight against a company with far more resources than you. That imbalance is real. It is also why the details matter: logs, inspections, and timestamps tell the story no matter how big the other side is.
Focus on healing. The paper trail is out there, and it can be found.
Pyramid Legal: Investigating Truck Crashes in Pasadena
If you were hurt in a truck accident in Pasadena or anywhere in Southern California, our attorneys can send preservation demands immediately, bring in reconstruction experts, and go after every party whose failures contributed to the crash. You get 24/7 direct access to an attorney and pay no fees unless we win. Visit us at 1055 E Colorado Blvd, Suite 500, Pasadena, CA 91106, call 818-946-0763, or learn more about our Pasadena truck accident lawyers.
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Want to know every party that may share the blame? Read who can be held liable in a truck accident.
This article is general information about truck accident investigations in California. It is not legal advice about your specific matter and does not create an attorney-client relationship.
Frequently Asked Questions
Can I get a copy of the truck's black box data myself?
Usually not directly. The data belongs to the truck’s owner or carrier, so it is typically obtained through a preservation demand followed by formal discovery or agreement in the case. Because the data can be overwritten as the truck operates, the request needs to go out as early as possible.
Does the CHP investigate every truck accident in California?
The CHP handles crashes on freeways and in its jurisdiction, and its specialized Multidisciplinary Accident Investigation Teams examine major collisions. Many truck crashes on city streets are investigated by local police instead. Either way, the official report is only one part of a full investigation.
What if the truck driver was an independent owner-operator?
The driver may still be operating under a motor carrier’s authority, and that carrier can share responsibility. Lease agreements, dispatch records, and the carrier’s insurance filings help show which company was responsible for the truck and the driver at the time of the crash.
How long does a truck accident investigation take?
The police or CHP report may take weeks, and a full investigation with expert reconstruction often takes months. The early steps, such as preserving electronic data, logs, and video, need to happen within days, even though the complete analysis comes later.
