Splitting, like riding can be done with "reasonable" safety. That is a relative term. The same riders who are not safe in general seem to be the ones who split recklessly. At the Love Ride this November, a couple died (they were crushed) when the rider tried to split past an 18 wheel tanker. I went to Sturgis with the rider some years ago and would say he was of average skill. This just shows that you must be on guard at all times!!
From KTLA: "The crash happened on the northbound 5 Freeway at Branford Street before 11 a.m. Sunday just as bikers were crowding the freeway for the the 28th annual Love Ride charity fundraiser.
According to California Highway Patrol officials, the driver of the motorcycle was
between lanes when he collided with a big rig, instantly killing himself and his female passenger."
The sand in this picture was to collect the blood, not oil.

Same scene from the opposite direction. Here is the bike and rig: