[cgriswald]

No, they shouldn't. I'm glad you weren't hurt, but your freak accident aside, most plastic bags are just plastic bags and human drivers are not expecting vehicles to yield to them. (There is also a difference between a plastic bag moving on the ground and one flying around.) If we are erring on the side of caution we shouldn't be creating a more probable hazard to avoid a less probable one.

And if we remove humans entirely from the equation what we get is traffic that comes to a stop because none of the vehicles can avoid or get past the plastic bag which floats around more-or-less randomly.