What Makes a Lane Change Illegal in California?

What the law says: Vehicle Code 22107

The whole section is one sentence:

"No person shall turn a vehicle from a direct course or move right or left upon a roadway until such movement can be made with reasonable safety and then only after the giving of an appropriate signal in the manner provided in this chapter in the event any other vehicle may be affected by the movement."

It contains two separate duties, and a driver can break either one:

1. Reasonable safety. The movement must be safe before it starts. This is the half that matters after a sideswipe.
2. A signal when someone could be affected. If any other vehicle may be affected, the signal comes first.

The neighboring sections that fill in the details

• Section 22108: "Any signal of intention to turn right or left shall be given continuously during the last 100 feet traveled by the vehicle before turning." A flick of the signal as the wheel turns does not meet it.
• Section 22109: no one may stop or suddenly slow down on a highway without first signaling to the driver immediately behind, when there is an opportunity to do so.

Together these describe the behavior the law expects: decide early, signal long, check, then move.

What it means in practice

Moves that cross several lanes at once, such as diving across the freeway for a late exit, are the classic unsafe lane change. Each lane is its own movement under the section, with its own check and its own signal.

The signal is not permission. A driver who signals and immediately moves into a gap that was not there has satisfied half the section and broken the more important half. The reverse also happens: a lane change into an empty freeway with no one around may be safe, but if a car two lanes over could be affected, the missing signal is still a violation.

Lane-change collisions are often one-witness, one-story events. Both drivers say the other one moved. What decides them is physical evidence: where the damage is on each car, the angle, dashcam video, and independent witnesses. The Insurance Commissioner's regulation makes a driver principally at fault only when their actions were at least 51 percent of the legal cause, so fault can be shared or disputed in a way people do not expect.

On the record, a conviction under section 22107 involves safe operation and counts as one point under section 12810(f). Whether it appears on an insurance review depends on whether traffic school was offered and completed, and how a given company rates one moving violation varies by insurance company.

What to do

1. Signal for several seconds before moving, not as you move; on a turn, the law asks for the last 100 feet.
2. Check mirrors and look over your shoulder for the blind spot every time.
3. Move one lane at a time on a freeway, signaling for each.
4. If you are in a lane-change collision, photograph both cars' damage and their final positions before they are moved, if it is safe to do so.
5. Exchange the information the law requires and report to the DMV within 10 days if the damage or injuries meet the threshold.

If a lane-change claim has affected your premium, you can compare quotes here.