It's perfectly legal in California for multiple vehicles to share lanes. For example. I can squeeze by you on the right if I am making a right hand turn and you are going straight. In fact a pet peeve of mine is morons that prevent this paticular activity by hogging the lane. ;-) Poor California we used to have the best drivers until all of the the illegals and Asians showed up :-(
I must say that it scared the bejeebeders out of me the first time it happened. I got to work and was sounding off about it. One of the guys in the office who rode a Harley, asked why I was upset at this LEGAL act. I had no idea until then that it was legal to ride between lanes on a 6 lane highway. Once I was informed, I was fine with it and much more cautious before changing lanes.