Has anyone seen research which looks at the impact of having other people in the bathroom upon hand washing rates?

My guess would be that having one or two other people in the bathroom with you raises washing rates above normal but that this disappears when the bathroom is crowded (for both wait and anonymity reasons).

This study focuses just on individuals – no comment on bathroom population density as a factor.

If my hypothesis holds true, and hand washing is a great way of preventing disease spread, cities would want to control bathroom density to promote co-usage, and also avoid building one stall public restrooms which would be single use by nature.