Sideswipe and Lane Change Accident: Who Is at Fault

Every state's traffic code requires a driver to drive as nearly as practicable within a single lane and not to move from it until the driver has ascertained that the movement can be made with safety. The driver in the lane has the right to stay there. A driver who moves into it and strikes a vehicle already there has violated the statute and is at fault, and the statement most lane-changing drivers make at the scene, that they did not see the other car, is an admission that they did not check.

The dispute arises because sideswipes leave both vehicles with similar damage, long scrapes along the side, and each driver claims to have been holding their lane when the other drifted over. Without more, insurers often assign shared fault, which halves both claims and, in contributory negligence states, ends them. The evidence that resolves it is the kind that shows lateral movement: which vehicle was angled, which had steering input, and what the witnesses in the surrounding lanes saw.

The simultaneous lane change is the exception where shared fault is right: two vehicles in the outer lanes of a three-lane road both move into the middle lane at the same moment and meet. Each driver had the same duty and each failed it, and the split is usually even unless one can show they were established in the lane first.

Merging onto a highway is a lane change into traffic that has the right of way. The merging driver must yield and find a gap; the through driver is not required to slow or move over, though in practice most do, and a through driver who accelerated to close a gap or who could easily have moved over may be assigned a share. A merge crash at the end of an on-ramp, where the merging driver ran out of ramp, is usually the merging driver's fault.

Blind spots are not a defense. A driver who moved into a lane without seeing a vehicle in their blind spot failed to check adequately; the mirror and the head check exist for that reason. Trucks have large blind spots along both sides, and a car traveling alongside a truck for an extended period is in a position the truck driver may not see, but the truck driver's duty to check before changing lanes is not reduced by the truck's design. Truck sideswipes of cars are common and the car's occupants are the ones hurt.

Lane drops, where a lane ends and traffic must merge, follow the same rule: the driver in the ending lane must yield to the continuing lane. Many states now require or encourage a zipper merge, alternating at the merge point, but the legal duty to yield remains with the merging driver unless the state's statute provides otherwise.

Suppose you were in the center lane of a three-lane highway when an SUV from the right lane moved into yours, striking your passenger side and pushing you into the concrete median barrier. You suffered a fractured wrist and a shoulder injury requiring surgery, with $51,000 in medical bills and eight weeks off work. The SUV's driver told police you had drifted into her lane.

Her insurer assigned fault 50/50 on the drivers' conflicting accounts. Your attorney obtained the police photographs, which showed the scrape on your car beginning at the front passenger door and running rearward, and the scrape on the SUV beginning at its rear quarter and running forward: the SUV's rear had swung into your lane as it angled across, the pattern of a vehicle moving left into a vehicle holding its lane. A driver two cars back had seen the SUV move without signaling and had left a number with the police. Your car's event data showed no steering input before the impact.

The fault assignment was withdrawn. The claim then addressed the injuries from the barrier strike, which were the serious part, and settled within the SUV driver's $100,000 policy after negotiation over the shoulder's lasting limitation. All figures are hypothetical; the damage-pattern analysis that resolves a sideswipe is the usual method.

The evidence in a sideswipe is the damage and the witnesses, and both are at the scene.

• Photograph both vehicles' damage from several angles, showing where the scrapes begin and end and the direction of the paint transfer, before anything is cleaned or repaired.
• Photograph the vehicles' final positions and the lane markings, and note which lane each vehicle was in before and after.
• Get names and numbers of drivers in the adjacent lanes who saw the lane change; they are the decisive witnesses.
• Write down what the other driver said, especially 'I didn't see you,' and tell the police.
• Ask whether either vehicle has a dashcam, and have both vehicles' event data preserved; steering input before the impact shows who moved.
• Get medical care the same day; a sideswipe that pushed you into a barrier or caused a spin is a serious crash.
• Do not accept a 50/50 assignment on the drivers' accounts alone; ask for the basis in writing and answer it with the damage analysis and witnesses.

The single-lane and safe-lane-change statutes exist in every state in nearly identical form, and a citation under them is evidence of negligence. Merge rules are statutory as well, with the merging driver yielding; a few states have enacted zipper merge provisions that modify the duty at lane drops. Comparative negligence decides what a shared-fault finding does: a reduction in pure comparative states such as California and New York; a reduction up to the bar in 51 and 50 percent states; and a complete bar in Alabama, Maryland, North Carolina and Virginia, where a 50/50 sideswipe leaves both drivers with nothing.

Commercial vehicle sideswipes bring the federal rules on driver qualification and hours, the carrier's liability for the driver, and the carrier's commercial policy, and the in-cab camera and event data that most carriers maintain. A truck's lane change into a car is defended on the car's position in the blind spot, and the truck driver's duty to check answers it.

Deadlines are the state's injury statute, one year in Tennessee and Kentucky, two in Texas, California, Florida and Georgia, three in New York and North Carolina. In no-fault states, the injured driver's PIP pays first regardless of the lane change dispute, and the claim against the other driver proceeds above the threshold.

Sideswipe damage can be read, and an experienced adjuster, investigator or reconstruction expert reads it. A vehicle moving laterally into another strikes it at an angle, and the contact typically begins at one end of the moving vehicle and progresses along the other vehicle's side; the scrapes on the vehicle holding its lane tend to run straight and parallel, while the scrapes on the moving vehicle show the angle. Paint transfer shows the direction of relative motion. Damage to mirrors, which protrude, often shows which vehicle's mirror struck the other's body first.

The final rest positions matter: a vehicle that ended up in the lane it claims to have been holding, and a vehicle that ended up angled across two lanes, tell a story. Tire marks from a vehicle that swerved to avoid the contact show its reaction. None of it is conclusive alone, and insurers that want a 50/50 split will say so, but together with witnesses and any camera footage the pattern resolves most disputes.

Event data from modern vehicles records steering wheel angle and lateral acceleration for the seconds before a crash. A vehicle with no steering input that experienced a sudden lateral acceleration was struck; a vehicle with a steering input toward the other lane moved. Requesting the data from both vehicles before they are repaired is the most reliable way to settle a sideswipe.

A sideswipe claim is decided by which driver left their lane, which the drivers' accounts never resolve and the damage pattern, the witnesses and the event data usually do. The questions to answer early are what the photographs of the damage show, whether any witness in an adjacent lane was identified, and whether event data was preserved before repair. Most personal injury attorneys work on contingency.

Ask Legal Matters is a free claim-review request service, not a law firm. Requests may be shared with independent attorneys and legal services partners who handle inquiries in your state, and an attorney must evaluate the facts before anyone can say what the claim is worth. If you were hurt in a sideswipe or lane change crash and the other driver says you moved, you can request a free claim review.

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• Accident on Icy Roads or in Bad Weather: Who Is at Fault
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• Amputation Injury Claim: Prosthetics and Lifetime Costs
• At Fault in a Car Accident? Comparative Negligence Explained
• What Is the Average Car Accident Settlement? What Sets the Value

Need local rules? Choose your state from the injury law guides hub or read the statute of limitations by state.