Abstract
By the increasing attention given to the pollution of the environment the way private persons transport themselves is considered. It is tried by all kinds of measures to decrease the number of car- kilometres and to replace them by public transport kilometres. One of the possible measures is to provide certain groups, students, soldiers, officers etc) with a so- called "free" public transport season ticket. In this paper a first survey is made in how far such a ticket for students will be efficient on the long term.