Lane splitting is generally quite safe if: a) Other motorists are expecting it and paying attention and b) The motorcyclist isn't going much faster than other traffic (if I remember correctly, where I live the law is that you shouldn't go more than 15mph above the speed of the traffic).

I used to lane split when I had a motorcycle as the highway traffic was terrible for my morning commute and it was generally fine, though you would occasionally get an idiot doing that thing some drivers do where they indicated a lane change as they were doing it and without checking mirrors so you have to be very careful.