[JacobAziza]

The only reason I bought my 250 was so I could lane split, which cut my commute across the Oakland / San Francisco Bay Bridge in half (30min to 15).

The express lane may not be the best analogy, but cutting in line isn't either (unless everyone is going up to a stop sign) because there is no point where each car needs to "check out". The slow down is just due to lane saturation. Traffic goes faster when there are fewer cars. And, like it says on the bicycle T-Shirt, a motorcycle not taking up a lane is "one less car".

The grocery store analogy would work only if the person with the hand cart slipped into a magical checkout lane which didn't actually exist previously, and which the shopping cart couldn't practically use anyway. Like if all the carts were full to the brim, and the person with a handbasket used the self-check lane, which would be impractical for a full cart. Then they are not only not holding back anyone else, they are getting out of everyone else's way.

If every single person in a mostly one-person-per-car commute was on a motorbike, it would be equivalent to doubling the amount of lanes, and the traffic jam wouldn't even exist. Each one person who lane splits brings that slightly closer. So not only do the motorcyclists not slow down other drivers by lane splitting, they actually speed them up just a tiny bit each.

As to it being unsafe, in all the statistics I've looked up on accidents, I haven't seen any evidence of it.