Are there laws or statutes governing the directing of traffic by citizens or "members of the public"?
A scenario I often encounter is one in which someone — typically another rider or pedestrian in a group that has stopped or slowed at road crossing — will signal an approaching driver to proceed across the flow of bicycle traffic. I realize that people who do this are trying to be helpful or courteous to the drivers, but they do so on behalf of others with whom they have not consulted and who they may not be aware of.
In particular, I'm wondering what the laws are in Massachusetts, though any information about New York City, London, Seattle and Vienna or other areas would be welcome.
Is someone who does this liable in any way for any accidents that might ensue? Are they legally permitted to direct traffic in this way? Do they assume any responsibility for others who may become involved in the consequences of their "traffic direction" (given that those others generally have no idea that such directions have been given)?