To motorists comply with the traffic rules on the roads Philadelphia were speed bumps. But do not these tools (and even the police are not alive, lying on the roadway), and cleverly drawn images have surround effects designed to force drivers to slow down. The purpose of this action was an attempt to not only make drivers less aggressive and start to follow the rules and remember that the speed limit - not recommended, as required for safe driving in residential areas of the city.
Such a trick (also calculated on an optical illusion) has been used for some time in West Salem (pcs. Ohio, USA). Only then on the roads does not draw. Just near schools and in residential areas near roads arranged the pictures of children in full growth - to drivers to slow down, thinking it was kids stand on the sidelines and is about to jump out on the road. The idea even interested in police stations and neighboring communities trying to protect children from speeding motorists.
Another similar idea (already calculated not only to drivers) - put on the streets of his district cardboard images of prostitutes in full growth. No, not for appearance (attractive layouts in such a little), and as a protest against an increase in rents in the area. This idea was born from the residents of Tel Aviv in Israel.