Vignette (sticker) is a form of road pricing imposed on vehicles, usually in addition to the compulsory road tax, based on a period of time instead of the usual road toll method based on distance traveled. It is currently implemented in some Central European countries (Austria, Slovenia, Switzerland, etc.) I am interested how were the sticker prices established. Is there any research showing what would be the "optimal" sticker prices in a particular case? What is the state of the art method?