Lane splitting by motorcycles is not illegal in California when done in a safe and prudent manner. Motorists should not take it upon themselves to discourage motorcyclists from lane splitting. Intentionally blocking or impeding a motorcyclist in a way that could cause harm to the rider is illegal (CVC 22400).
Here's somewhere with similar driving laws.
http://www.sacbee.com/news/local/tra...20Analysis.pdf