How to Prove Liability in a California Personal Injury Case

A serious injury does not automatically create a personal injury claim. To recover compensation, you generally must prove that another person, business, or public entity was legally responsible for the harm.

That requires more than showing that someone made a mistake. You need evidence establishing what happened, why it happened, how the defendant's conduct caused the injury, and the extent of the resulting harm.

In a disputed case, some of the most important evidence can disappear quickly. For that reason, proving liability often begins with a thorough investigation long before a lawsuit is filed.

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What Do You Have to Prove in a Personal Injury Case?

Many California personal injury cases are based on negligence.

California's general rule of reasonable care is found in Civil Code § 1714, which generally makes a person responsible for injuries caused by a failure to use ordinary care in managing their person or property.

At trial, California juries are instructed on the essential elements of negligence through CACI No. 400, Negligence: Essential Factual Elements. The plaintiff must prove:

1. The defendant was negligent.
2. The plaintiff was harmed.
3. The defendant's negligence was a substantial factor in causing that harm.

Lawyers commonly analyze a negligence claim in terms of duty, breach, causation, and damages:

Duty. The defendant owed the injured person a legal duty to use reasonable care.

Breach. The defendant failed to meet the applicable standard of care.

Causation. The defendant's negligence was a substantial factor in causing the injury.

Damages. The injured person suffered harm as a result.

Each part matters. A person may act carelessly without causing an injury. Conversely, someone can suffer a devastating injury without another person being legally responsible.

A successful negligence claim requires evidence connecting the defendant's conduct to the harm suffered.

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What Does Negligence Mean?

Negligence is measured against what a reasonably careful person would have done under the circumstances.

CACI No. 401, Basic Standard of Care explains that a person can be negligent by doing something a reasonably careful person would not do or by failing to do something a reasonably careful person would do.

The specific conduct that constitutes negligence therefore depends on the case.

For example:

• A driver may be negligent by failing to keep a proper lookout.
• A trucking company may be negligent in maintaining a commercial vehicle.
• A property owner may fail to address a dangerous condition.
• A business may fail to use reasonable care in hiring, training, or supervising an employee.
• A driver, bicyclist, pedestrian, or other road user may violate a safety law intended to prevent a collision.

The question is not whether someone made any mistake. It is whether the person's conduct fell below the standard of reasonable care and contributed to the injury.

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What Evidence Is Used to Prove Liability?

Strong personal injury cases are built from evidence, not assumptions.

The evidence needed varies by case, but serious injury investigations often involve several different sources of proof.

Physical Evidence

The physical evidence may provide the clearest picture of what happened.

Depending on the case, this may include:

• Photographs and video of the scene
• Vehicle damage
• Skid marks and debris
• Roadway conditions
• Damaged bicycles, motorcycles, helmets, or other equipment
• A defective product or component
• Surveillance footage
• Traffic-camera footage
• Measurements and inspections of the scene

Physical evidence can change quickly. Vehicles are repaired or destroyed. Road conditions change. Products are discarded. Businesses routinely overwrite surveillance footage.

Identifying and preserving important evidence early can make a substantial difference in what can later be proven.

Electronic Evidence

Electronic data has become increasingly important in serious injury cases.

A car collision may involve event data recorder information showing vehicle speed, braking, throttle position, or other information shortly before an impact.

A serious truck accident may involve additional evidence such as:

• Electronic logging device records
• GPS data
• Engine or vehicle control module data
• Onboard cameras
• Dispatch communications
• Electronic maintenance records
• Driver communications

Our guide to the truck accident investigation process explains why preserving this evidence quickly can be critical.

Cell phone records, photographs, text messages, and other electronic information can also become important depending on the circumstances.

Documents and Records

Documents can reveal facts that are not visible at the accident scene.

Depending on the case, relevant records may include:

• Police or incident reports
• Inspection and maintenance records
• Employee training records
• Company safety policies
• Driving records
• Prior complaints or incidents
• Traffic engineering documents
• Government records
• Medical records
• Employment and wage records

In claims against businesses or government entities, records created before the injury can be particularly important because they may show what the defendant knew before anyone was hurt.

Witness Testimony

Independent witnesses can help resolve conflicting accounts of how an incident occurred.

Other witnesses provide different pieces of the case. Employees may explain company procedures. Treating physicians can describe injuries and treatment. Family members may explain how catastrophic injuries changed someone's ability to work, function, and participate in everyday life.

Witnesses are usually easier to locate, and their memories are often clearer, when the investigation begins promptly.

Expert Analysis

Some questions require specialized knowledge.

Depending on the case, experts may include:

• Accident reconstruction experts
• Traffic engineers
• Mechanical engineers
• Medical specialists
• Biomechanical experts
• Human-factors experts
• Vocational rehabilitation experts
• Life-care planners
• Economists

Expert testimony can help determine what happened, explain complicated evidence, and establish issues that a jury cannot reasonably evaluate without specialized knowledge.

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Why Causation Can Be the Hardest Part of a Case

Proving negligence is not enough. The plaintiff must also prove that the negligence caused the claimed harm.

California juries are instructed on this issue through CACI No. 430, Causation: Substantial Factor.

A substantial factor is more than a remote or trivial contribution to the harm. The defendant's conduct does not, however, have to be the only cause.

Consider a driver who runs a red light and causes a collision. The traffic violation may provide strong evidence of negligence. But the defense may still argue that the collision did not cause some or all of the injuries being claimed.

Causation can become especially important when an injured person has:

• A preexisting medical condition
• Prior injuries
• Delayed symptoms
• Multiple injuries
• More than one traumatic event
• Complicated future medical needs

Medical records, diagnostic imaging, treating physicians, and medical experts can become critical to showing the connection between the incident and the resulting harm.

What If More Than One Thing Caused the Injury?

An injury often has more than one contributing cause.

CACI No. 431, Causation: Multiple Causes addresses this situation. A defendant cannot avoid responsibility simply because another person, condition, or event also contributed to the plaintiff's harm. The question remains whether the defendant's negligence was a substantial factor.

This can be particularly important in serious cases involving multiple vehicles, multiple defendants, dangerous road conditions, defective products, or a combination of factors.

A thorough investigation should therefore look beyond the most obvious cause of an accident.

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When a Safety-Law Violation Helps Prove Negligence

A violation of a safety statute or regulation can sometimes help establish negligence under a doctrine known as negligence per se.

California Evidence Code § 669 creates a rebuttable presumption of a failure to exercise due care when specific requirements are satisfied.

Among other things:

1. The person must have violated a statute, ordinance, or regulation.
2. The violation must have caused the injury.
3. The injury must have resulted from the type of occurrence the law was designed to prevent.
4. The injured person must be within the class of people the law was intended to protect.

California juries may also receive CACI No. 418, Presumption of Negligence per se when the doctrine applies.

Traffic laws are a common example. A violation involving a red light, right of way, unsafe speed, or another safety rule may help establish negligence when the legal requirements are satisfied.

A statutory violation does not automatically establish the entire case. Causation, damages, comparative fault, and other issues may still be disputed.

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What If the Injured Person Was Partly at Fault?

California follows a system of comparative fault.

The defense may argue that the injured person's own negligence contributed to the harm. Under CACI No. 405, Comparative Fault of Plaintiff, the defendant has the burden of proving that the plaintiff was negligent and that the plaintiff's negligence was a substantial factor in causing the harm.

If the defense proves comparative fault, the plaintiff's damages are reduced according to the percentage of responsibility assigned to the plaintiff.

For example, if a jury finds $1 million in damages but determines that the plaintiff was 20 percent responsible, the recovery would generally be reduced by 20 percent.

Comparative fault therefore becomes an important issue in many cases.

An insurance company may argue that:

• A driver was speeding.
• A motorcyclist was riding unsafely.
• A bicyclist was outside a bike lane.
• A pedestrian was inattentive.
• Someone failed to notice a dangerous condition.

Those allegations should be tested against the evidence rather than accepted at face value.

Our guide to how fault is determined in San Diego car accidents explains how these disputes arise after vehicle collisions.

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How Liability Differs by Type of Personal Injury Case

The basic concepts of negligence and causation apply to many personal injury cases, but the evidence and legal rules can vary significantly depending on how the injury occurred.

Car Accidents

A car accident case may turn on traffic laws, vehicle damage, witness testimony, surveillance footage, electronic vehicle data, and accident reconstruction.

Our guide to how fault is determined after a car accident examines those issues in more detail.

Truck Accidents

Commercial truck cases often involve evidence that does not exist in an ordinary automobile collision.

Electronic logs, driver qualification records, inspection documents, maintenance records, dispatch communications, onboard data, cargo information, and company safety practices can all matter.

Because some of this evidence can disappear, a truck accident investigation should begin promptly.

Bicycle and Pedestrian Accidents

Bicycle accidents and pedestrian accidents often involve questions about sight distance, driver attention, right of way, visibility, traffic signals, and roadway design.

Video, signal timing records, roadway measurements, electronic vehicle data, and reconstruction can become particularly important when the driver claims the bicyclist or pedestrian suddenly entered the roadway.

Premises Liability

In a premises liability case, proving that a dangerous condition existed may not be enough.

A central issue is often whether the property owner created the dangerous condition or knew, or reasonably should have known, about it in time to correct the condition or provide an adequate warning.

Our guide to proving liability in a premises liability case explains these requirements in more detail.

Dangerous Road Conditions

Cases involving a dangerous public road require a different legal and factual analysis.

Under Government Code § 835, a public entity can be liable for an injury caused by a dangerous condition of public property when the statute's requirements are satisfied.

Evidence in a dangerous roadway condition case may include:

• Collision-history data
• Engineering plans
• Traffic studies
• Signal timing records
• Sight-distance measurements
• Maintenance records
• Prior complaints
• Government correspondence
• Traffic engineering analysis

These cases require careful investigation because liability against a public entity is governed by specific statutes and defenses.

Defective Products

A product defect case may involve strict liability rather than ordinary negligence.

A claim can arise from a manufacturing defect, defective design, inadequate warning, or other product-related theory.

Preserving the actual product is often essential. Engineers and other experts may need to inspect and document it before its condition changes.

Dog Bites

California also has a specific statute governing many dog-bite claims.

Under Civil Code § 3342, a dog owner is generally liable when the dog bites a person who is in a public place or lawfully in a private place, subject to the statute's requirements.

This means a traditional negligence claim is not always necessary to establish liability for a bite. Different rules may apply when a dog causes an injury without actually biting someone.

Learn more about California dog-bite law on our dog bite practice page.

Catastrophic Injury and Wrongful Death

When an accident causes a traumatic brain injury, spinal cord injury, permanent disability, or wrongful death, proving responsibility is only part of the case.

The evidence must also establish the consequences of the injury or death.

Depending on the circumstances, this may require medical specialists, vocational experts, life-care planners, economists, and other professionals to evaluate future care, lost earning capacity, and other long-term losses.

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How We Investigate Serious Personal Injury Cases

In a serious case, one of the questions we ask at the beginning is:

What evidence would we want if we had to try this case years from now?

Then we work backward.

Depending on the case, that may mean:

• Preserving a vehicle, bicycle, product, or other physical evidence
• Sending preservation demands
• Locating surveillance or traffic video
• Interviewing witnesses
• Obtaining electronic data
• Inspecting and documenting the scene
• Requesting government records
• Obtaining company records
• Retaining appropriate experts

We also look beyond the most obvious explanation.

A collision may involve more than a negligent driver. A trucking company's safety practices may have contributed to a crash. A dangerous roadway may have increased the risk of a predictable collision. A defective vehicle component may have caused an accident or made the resulting injuries worse.

Finding those issues requires investigation.

The goal is not simply to collect enough evidence to submit an insurance claim. It is to understand what happened, identify everyone who may be legally responsible, and preserve the evidence necessary to prove the case.

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Why Early Investigation Matters

Evidence does not wait for a lawsuit.

Surveillance video may be overwritten. Vehicles may be repaired or salvaged. Roadway conditions can change. Electronic information can disappear. Witness memories become less precise with time.

There are also legal deadlines.

Under Code of Civil Procedure § 335.1, a lawsuit for personal injury or death caused by another person's wrongful act or neglect generally must be filed within two years.

There are important exceptions, and some claims have much shorter deadlines.

Claims against California public entities require particular attention. Under Government Code § 911.2, a claim relating to personal injury or death generally must be presented to the public entity within six months after the claim accrues.

Our guide to the California personal injury statute of limitations explains these deadlines and some of their exceptions.

The safest approach in a serious case is to investigate potential defendants and deadlines early rather than assume responsibility is obvious.

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Building a Case That Can Be Proven

The strongest personal injury cases establish every link in the chain: what happened, who was responsible, what they did wrong, how that conduct caused the injury, and the full extent of the resulting harm.

At Hulburt Law Firm, we focus on serious personal injury and wrongful death cases throughout San Diego County. We investigate the facts, preserve important evidence, work with qualified experts when necessary, and prepare cases with trial in mind from the beginning.

If you or someone you love has suffered a serious injury because of another person's negligence, contact Hulburt Law Firm for a free and confidential case review.