The California Highway Patrol and other statewide traffic safety groups have created a set of written guidelines on motorcycle “lane-splitting”.
The guidelines set by the groups including the CHP, the Department of Motor Vehicles and Office of Traffic Safety, say motorcyclists can ride between two cars if there is room, but only at speeds no more than 10 miles-per-hour faster than the vehicles they’re passing. The rules also say that motorcyclists should not attempt the move at full freeway speeds, or in any traffic going faster than 30 mph.
So, to summarize, if traffic is going 30 mph or slower you are allowed to lane split if there is room to do so but you can’t be moving more than 10 mph faster than traffic.
BTW – California is the only state in the country that allows lane-splitting.