Traffic on the northbound 405 is crawling up the Sepulveda Pass toward the Valley. You are holding your lane when a pickup two cars ahead of you in the next lane jerks right, closes the gap, and scrapes the full length of your driver's side. At the shoulder, the other driver says you sped up to block him. There is no camera you know of, and the only other witness drove off.
Sideswipe crashes feel minor compared to a rear-end or a T-bone, but they cause real injuries, especially when a car is pushed into a barrier or into another lane. They also produce more fault disputes than almost any other crash type, because each driver usually says the other one moved.
Quick answer: In California, a driver must stay as nearly as practical within a single lane and may not move from it until the move can be made with reasonable safety, under Vehicle Code section 21658(a). A driver must also signal before changing lanes when another vehicle may be affected, under Vehicle Code section 22107. In a sideswipe, the driver who left their lane without enough room is usually the one at fault, but fault can be shared under California's pure comparative fault rule. The evidence that proves who moved, including damage patterns, dashcam video, and witness statements, should be gathered right away.
Key Takeaways
- Vehicle Code section 21658(a) bars leaving a lane until the move can be made with reasonable safety.
- Vehicle Code section 22107 requires a signal when a lane change may affect another vehicle.
- The driver who changed lanes is usually at fault, but California's pure comparative fault rule lets fault be split.
- Damage location, paint transfer, dashcam footage, and independent witnesses usually decide who moved.
- Most injury claims must be filed within two years under Code of Civil Procedure section 335.1.
What Does California Law Say About Changing Lanes?
Two Vehicle Code sections do most of the work. Section 21658(a) applies on roadways divided into two or more clearly marked lanes for traffic in one direction, which describes the 405 through the pass. It says a vehicle shall be driven as nearly as practical entirely within a single lane and shall not be moved from the lane until the driver has first ascertained that the movement can be made with reasonable safety.
Section 22107 says no person shall turn a vehicle from a direct course or move right or left upon a roadway until the movement can be made with reasonable safety, and then only after giving an appropriate signal if any other vehicle may be affected by the movement.
Notice what these rules do not say. They do not say a signal makes a lane change legal. A driver who signals and then moves into a space that is not there has still violated section 21658. And they do not give the driver already in the lane a license to ignore what is happening around them.
How Is Fault Decided in a Sideswipe?
When a driver violates a safety statute and that violation causes the kind of harm the statute was designed to prevent, California presumes negligence under Evidence Code section 669. In a sideswipe, the main question is factual: which car crossed the line?
Fault is then assigned under California's pure comparative fault system, adopted in Li v. Yellow Cab Co. (1975) 13 Cal.3d 804. If a jury finds the lane changer 80 percent responsible and the other driver 20 percent responsible for speeding up into the gap, each recovers damages reduced by their own share. Our guide to comparative negligence in California explains how that math works.
What if both drivers moved into the same lane at once?
This happens on multi-lane freeways when two cars from opposite sides merge toward the same middle lane. Each driver owed the same duty under section 21658, so fault is often shared. The deciding evidence is usually timing: who started moving first and who had a clear view of the other.
What Evidence Proves Who Changed Lanes?
The damage itself tells a story. A car that moved into another lane usually shows damage starting at its front corner and running back, while the car that was struck often shows damage from the side toward the rear. An accident reconstruction expert can read paint transfer, scrape direction, and crush depth.
Other evidence that matters:
- Dashcam and phone video. Many commuters run dashcams. Ask anyone who stopped, and check rideshare drivers who were nearby.
- Witnesses. Get names and phone numbers at the scene. Independent witnesses carry weight because they have no stake in the outcome.
- The collision report. On the 405 and other state freeways in Los Angeles County, the California Highway Patrol usually investigates. A report can be requested from the CHP area office that handled the call. If the report gets the facts wrong, our post on what to do when a collision report blames you covers how to respond.
- Vehicle data. Many newer vehicles record speed and steering inputs in the seconds before a crash. That data should be preserved before the car is repaired or sold.
- Phone records. If a lane change was caused by distraction, phone records can show it, though they usually require a subpoena after a lawsuit is filed.
What Injuries Happen in Sideswipe Crashes?
Sideswipes are often low-speed, but they are not always harmless. A side impact pushes the body laterally, a direction seat belts handle less well than frontal forces. Common injuries include neck and back strain, shoulder injuries from the belt and door, head injuries from striking the window, and injuries from a secondary impact if the car is pushed into a center divider or another vehicle.
If you feel sore the next day, get evaluated. Insurers use gaps in treatment to argue that an injury was minor or came from something else.
What Should I Do After a Sideswipe on the Freeway?
- Get to safety. If no one is hurt and the cars can move, get out of live traffic if you can do so safely, and turn on your hazard lights.
- Call 911 if anyone is hurt. Vehicle Code section 20001 requires drivers involved in an injury crash to stop, render reasonable assistance, and exchange information.
- Photograph both cars before they move if it is safe, including lane position, damage on both vehicles, and any skid or scrape marks.
- Do not argue fault at the scene. Statements like "I didn't see you" get repeated in reports and recorded statements.
- Report to DMV if required. Vehicle Code section 16000 requires a report within 10 days when a crash causes injury, death, or property damage over $1,000.
- Notify your own insurer, but think carefully before giving a recorded statement to the other driver's insurer.
Frequently Asked Questions
Is the driver who changed lanes always at fault?
No. That driver is usually at fault, but the other driver can share fault for speeding up to close a gap, drifting out of their own lane, or driving distracted. California's pure comparative fault rule splits responsibility by percentage.
What if there are no witnesses and no video?
Fault can still be proven through damage patterns, vehicle data, and expert analysis. These cases are harder, which is why early preservation matters.
Does a turn signal protect me if I changed lanes?
Not by itself. Section 22107 requires a signal, but section 21658 separately requires the lane change to be reasonably safe. A signal followed by an unsafe move is still a violation.
Who investigates a crash on the 405?
On state freeways in Los Angeles County, the California Highway Patrol usually responds and prepares the report. On city streets, the Los Angeles Police Department or the local police or sheriff's station usually responds. Our Los Angeles accident guide covers local agencies and next steps.
How long do I have to make a claim?
Generally two years from the injury under Code of Civil Procedure section 335.1. If a government vehicle was involved, a written claim is usually required within six months under Government Code section 911.2.
Hurt in a Lane-Change Crash? Geller Legal Can Help.
Sideswipe cases often become one driver's word against another's. The side that preserves the dashcam video, the vehicle data, and the witness statements first is usually the side that gets believed.
Geller Legal | Personal Injury Attorneys moves quickly to secure the evidence, works with reconstruction experts when fault is disputed, and handles the insurers so you can focus on recovering. Learn more about our California car accident practice.
We serve injured clients throughout California, with offices in Walnut Creek, Oakland, and Los Angeles. If you were hurt in a sideswipe or lane-change crash, call us at 213-770-4870 for a free, confidential consultation with Attorney Michael Geller.