Lane splitting by motorcycles is not illegal in California when done in a safe and prudent manner. Traffic safety organization developed a few tips for lane splitting.
Tips for motorcyclists:
Step 1. Do not travel more than 10 mph faster than other traffic
Step 2. It is unsafe to lane split when the traffic is moving at 30mph or faster
Step 3. It is safer to split between lanes #1 and #2
Step 4. Consider the whole environment before splitting including differential speed of traffic, lane width, roadway, weather and lighting conditions
Step 5. Be alert and anticipate movements of other roadway users
Tips for other roadway users:
Step 6. Scan mirrors and blindspots frequently, especially before changing lanes and making turns
Step 7. Signal before changing lanes or merging into traffic
Step 8. Increase following distance behind a motorcycle to 3-4 seconds so they have time to maneuver in heavy traffic
Step 9. Avoid distracted driving and keeps your eyes on the road
Step 1. Be respectful, impeding or blocking a motorcyclist in a way that can cause harm is illegal
All roadway users need to take reasonable precautions and to act responsibly so everyone has a safe journey to their respective destinations.