No disrespect to you 4in6, but if there is such a law, how come it was never mentioned when I attended California Motorcycle Safety school?
In fact we students asked our instructor the very same question: is it legal to split lanes? He told us that it is
legal so long as you don't go more than 10 mph faster than surrounding traffic, and so long as you don't exceed the maximum speed limit.
I did a little research on the Net, and came accross this FAQ page
maintained by the California Highway Patrol. According to the CHP...
Lane splitting by motorcycles is permissible under California law but must done in a safe and prudent manner. The motorcycle should be traveling no more than 10 mph faster than surrounding traffic (without exceeding the speed limit) and not come close enough to that traffic to cause a collision.
I don't know where you got this 45 mph limit to lane splitting, but you could help us out by posting the California Vehicle Code number so we can look it up. The last thing I want to do is get a ticket for splitting lanes at 46 mph.