How is Fault Determined in a Lane-Change Accident?

It’s a scenario that plays out every day on the busy multi-lane highways around Tacoma, like I-5 or SR 16. You’re driving along, staying in your lane, when suddenly a car from the next lane over merges into your space. You slam on your brakes and swerve, but it’s too late. The sickening crunch of metal follows. After the initial shock, the other driver insists, “You were in my blind spot!” or “You sped up and wouldn’t let me in!”

Lane-change and sideswipe accidents are among the most common types of collisions, and they are also the most frequently disputed. Unlike a rear-end collision where there’s a strong presumption of fault, a lane-change accident often becomes a classic “he said, she said” standoff.

So, how do insurance companies and the law sort it out? Fault is not a matter of opinion; it is determined by applying Washington State’s traffic laws to the physical evidence and witness testimony.² Understanding the “rules of the road” for changing lanes is the key to proving your case.

Useful Information for You: In a Nutshell

• The Burden is on the Merging Driver: Under Washington law, the driver who is attempting to change lanes has the primary duty to ensure it is safe to do so before they move over.³
  
   
• Right-of-Way is Key: The driver already established in a lane has the right-of-way. The merging driver must yield to the traffic that is already there.
• Fault is Proven with Evidence: Because these are often word-vs-word cases, physical evidence is critical. The location of the vehicle damage, photos of the scene, witness statements, and dashcam footage are essential.⁴
  
   
• “Blind Spot” is Not a Legal Excuse: While blind spots are real, every driver is responsible for checking theirs before moving over. Claiming “they were in my blind spot” is an admission of failure to look, not a valid legal defense.
• Comparative Fault May Apply: If both drivers were acting negligently (e.g., one made an unsafe merge while the other was speeding), fault can be shared under Washington’s comparative fault rule.

The Legal Duty of the Driver Changing Lanes

Washington State law (specifically RCW 46.61.140) is very clear on this point. A driver attempting to move from one lane to another must do so only when it is safe. This means the merging driver has a legal duty to:

1. Signal Their Intention: They must use their turn signal to indicate their intent to change lanes.
2. Look and Check Blind Spots: They must look in their mirrors and physically turn their head to check their blind spot to ensure the lane is clear.
3. Yield the Right-of-Way: They must yield to any vehicle that is already in the lane they intend to enter.⁵
   
    

Because the burden of safety is placed so heavily on the driver initiating the lane change, they are most often found to be at fault in a sideswipe or merge collision.

When Can the Other Driver Be at Fault?

While the merging driver is usually held liable, there are situations where the driver who was already in the lane can be found partially or even fully at fault. This typically happens if that driver was acting negligently and made the safe lane change suddenly unsafe.

Examples include:

• Speeding: If the driver in the lane was significantly exceeding the speed limit, they may have closed the gap much faster than the merging driver could have reasonably anticipated.
• Distracted Driving: If the driver in the lane was on their phone or otherwise distracted and failed to react to a properly signaled lane change, they could share fault.
• Intentionally Blocking: In a rare road-rage scenario, if a driver intentionally speeds up to prevent another car from merging, they are acting negligently and can be held liable.

The Evidence That Decides the Case

Because the drivers’ stories often conflict, the physical evidence is what truly tells the story.

• Location of Damage: The position of the dents and scrapes is crucial. For example, damage to the front corner of the merging car and the rear quarter panel of the other car often indicates the merging driver tried to cut in without enough space.
• Photos of the Scene: Pictures showing the final resting positions of the cars can help experts reconstruct the angle of impact.
• Witness Statements: An independent witness who saw the merge happen is the most powerful evidence you can have. Their neutral account can confirm who had the right-of-way.
• Dashcam Footage: This is the ultimate tie-breaker. A clear video of the incident can immediately and definitively establish fault.

Navigating a disputed lane-change accident requires a meticulous investigation and a thorough understanding of the law. You must build a case based on facts to counter the other driver’s claims.

If you’ve been in a lane-change or sideswipe accident in the Tacoma area and the other driver is blaming you, it is crucial to get professional legal help. Search the Car Accident Lawyer Directory Tacoma to find and compare trusted local attorneys who can analyze the evidence, build a powerful case, and fight to protect your rights.

References

• Revised Code of Washington (RCW 46.61.140) – Driving on roadways laned for traffic:The official state law that establishes a driver’s duty to ensure it is safe before moving from their lane.https://app.leg.wa.gov/RCW/default.aspx?cite=46.61.140
• Washington Pattern Jury Instructions (WPI 70.03) – Duty of Driver—Lane Change:The official instruction for juries that clearly states the driver changing lanes has the primary duty to yield and see what is visible.https://www.courts.wa.gov/superiori/pattern_jury_instructions/WPI%2070.03%20Duty%20of%20Driver%20-%20Lane%20Change.pdf