Lanes of cars and trucks back up on the freeway during commute hours and at stop lights. Often, there is a space between the lanes of stopped traffic big enough for a motorcycle to pass. Zipping up between lanes of traffic is known as lane splitting. Almost everyone agrees that it can be dangerous. But you'll find a wide range of views on the question of whether it is legal.
TL;DR (Too Long; Didn't Read)
Motorcycles can legally lane split in California. Some state laws expressly forbid it, but most are silent as to whether it is legal or not, leaving it up to the police and the courts to determine.
What is Lane Splitting?
If you've ever seen motorcycle riders traveling beside each other in one lane of the freeway, you might think that this is splitting lanes, but it isn't. Lane splitting is when a motorcycle passes in between two lanes of stopped or slowly moving cars. This often occurs in backed-up traffic. In a city, it allows the rider to get to the front of the line at a traffic light. On freeways, motorcycles can avoid the stop-and-goes of traffic jams by lane splitting.
Obviously, with motorcycles and four-wheeled vehicles in such tight concentration, accidents can happen. Most experts agree that lane-splitting can be dangerous and isn't a very wise practice for someone new to motorcycle riding. One moment of inattention, and the rider can hit a car or be hit by one. If an accident happens while a motorcycle is lane splitting, one important question in determining fault is whether lane splitting is legal in that state.
Safety Benefits of Lane Splitting
It is always more dangerous to ride a motorcycle than to drive a car or truck. Balancing on two wheels without the protection that a car offers makes motorcycle riders particularly vulnerable. Add to that the fact that they are smaller and harder to see than a car, and motorcyclists have a much higher safety risk than the ordinary driver.
Getting caught in congested traffic is one of the most dangerous situations for any motorcyclist. Stop-and-go traffic increases the risks of motorcycles getting rear ended by inattentive drivers, to disastrous consequences. Even slight contact can cause injury or death for a motorcyclist.
Where is Lane Splitting Legal?
In most states, lane splitting is not discussed in driving laws. It appears neither on the list of forbidden types of driving, nor on the list of permitted driving maneuvers. In these states, police officers often classify it as illegal, and courts may follow suit, depending on the circumstances.
But in California, lane splitting is officially legal – in fact, it is reportedly the only such state. According to California Vehicle Code 21658.1, effective the first day of 2017, lane splitting is "driving a motorcycle between rows of stopped or moving vehicles in the same lane including on both divided and undivided streets, roads and highways."