Well, as most others on here seem to agree, it would take a catastrophic jolt to knock a bike off one of these racks, or a collision. In the case of a collision, nothing will save my bike from damage, barring some miracle of the bike flying off just right and landing softly on the other side of said collision. In the event the bike falls off due to an elephant sized pothole while moving, i guess an unlocked bike would just be crushed and down the road. If if was locked, and fell off, i suppose it could do a little more cosmetic damage to the bus if it were dragged for a while, but as stated, that is highly unlikely. Then again, it could prevent it from striking an innocent bystander.

I am an engineer, but certainly not a physicist. I just think that any freak accident that might happen would probably lead to very similar results whether the bike is locked or not.

As far as the design of the racks go, to my knowledge there are no designed "crush zones" or "failure welds" to minimize impact forces. If there are, i still cant imagine a locked vs. unlocked bike would really change the outcome very much. Either way, there will be a bike in this crushing metal to provide many variables.

I see your concern about lawsuits, but i think until a bus is in a collision, and a front mounted bike crashes through the windshield, pokes the driver in the eye, and the cause can be directly attributed to the lock, it will not be an issue. Even then, i don't think they would change the design (although they might stop using them). Kinda like high-rise building design pre/post 9/11. Buildings were never designed for that kind of impact and fire because no one had ever conceived of it. Now that we have, most buildings are still not designed for it, because the odds are very minimal and even the best structures are vulnerable to an infinite number of strange variables.