California is the only state in the country that permits safe lane splitting, or filtering, as it's more commonly known abroad. In other countries it is expected for bikes, scooters, and motorcycles to lane split. I've heard that in California it was tolerated in the old days because air-cooled motorcycles kept overheating in traffic and it just made sense that they got to keep moving. Now it is common practice regardless of the type of bike, but it is highly misunderstood and seen as reckless and dangerous by those who don't ride, or haven't learned the facts about this technique.
As a new rider I also thought this seemed crazy at first but as my confidence and my knowledge grew, I began to understand the benefits of lane splitting. It is counter intuitive, but when done sensibly, it can actually be safer than tucking in to the stop and go of regular traffic flow.
There are a lot of distracted drivers out there and most don't have motorcyclists in mind. Starting and stopping introduces many occasions for rear and front end collisions, and motorcyclists don't often fare well when bumped, even at low speeds, by large vehicles. Congestion also increases when bikes take up another space and don't flow through toward their destination. Lane splitting is entirely optional and no one should do it if they aren't comfortable.
When I started, I did this pretty tentatively. One car here, another few cars there, always pulling back into the lane when I could. This helped confirm that it was possible and got me used to the sensation of slipping in between slow moving vehicles. After a while I got more comfortable and employed this tactic more and more, but always stayed super alert. This isn't a thing to do when you are tired or feeling off your game.
Here are some tips that helped me learn how to filter with care.
1. The space between cars is actually the safest space.
This seems weird but it's true. It is really unlikely that two cars cruising next to each other will suddenly smash into each other, side to side. They can certainly drift toward one another and close the gap dangerously, but this is rare and cars generally stay consistently apart for the second or two you happen to be between them.
2. A car with an empty lane next to it is the REAL danger.
Turn signals are often only used by drivers to let you know they just changed lanes. Throw the thought that they might be trying to let you know what they plan to do out the window. As such, many cars will leap into the lane next to them when they see that it is clear of vehicles (this doesn't include bikers because A) they aren't looking for bikers and B) because you probably just emerged from 6 cars behind, filtering through traffic, and they have no clue that it's even possible for you to be there. They base their decisions on interactions with other cars and assume other spaces to be clear. This is just force of habit. So when you see a car with an open space next to it, beware the sudden lane change. I usually move into the center of the open lane which makes me more visible by placing me in a place where traffic is expected to be, and it also positions me better if I need to escape by moving over to the next lane.
3. Unpredictable things happen.
Don't fly through at such a high rate of speed that you can't react in time if someone changes lanes ahead of you. Those people who ride through 10mph traffic at 50mph are just tempting fate. I'd rather save my luck for other occasions.
4. Stay alert.
Sometimes you get concentration fatigue and just need a break. Go ahead and pull back in to traffic and take it easy for a while. Lane filtering may be safe when done right but it can be tiring to exercise that level of heightened focus. It can make regular attentive riding seem relaxing.
5. Use your judgement.
If that gap seems to small don't risk it. What's the rush? There will be another opportunity soon enough as traffic rearranges itself. If it's raining, the road is slippery, visibility is down, you are carrying a wide load, you don't feel up to it, traffic feels oddly aggressive, etc... save the filtering for another day.
6. Watch out for other motorcycles!
There will inevitably be other bikers out there comfortable with lane splitting at a higher speed. Keep a look out for them approaching from behind and make room. Also, when you decide to START lane splitting, MAKE SURE there isn't another motorcyclist already in that gap. We sometimes forget to watch out for each other. On the other hand, be courteous and careful when passing other bikers in congested situations. Realize they might be about to make a move and pass with caution.
Here is some additional info on lane splitting.
From the National Agenda for Motorcycle Safety report: “Study of the safety implications of lane splitting.”
“A motorcycle’s narrow width can allow it to pass between lanes of stopped or slow-moving cars on roadways where the lanes are wide enough to offer an adequate gap. This option can provide an escape route for motorcyclists who would otherwise be trapped or struck from behind. There is evidence (Hurt, 1981) that traveling between lanes of stopped or slow-moving cars (i.e., lane splitting) on multiple-lane roads (such as interstate highways) slightly reduces crash frequency compared with staying within the lane and moving with other traffic.
“Although lane splitting is allowed in just a few areas of the United States, notably California, it appears to be worthy of further study because it offers a means of reducing congestion in addition to possible safety benefits. It is widely used in many other countries.”
The California Highway Patrol recently issued their Lane Splitting Guidelines
I hope this gets adopted in Illinois before I move there because it will be a hard thing to unlearn for the sake of a relatively arbitrary ban that isn't supported by the facts. I'm sure I'll get used to it though. Winter will probably be the tougher thing to abide.