Without a doubt, the bicycle is the most ecologically acceptable mode of transportation. Nonetheless, for a long time, it had been almost ignored in transportation planning. Only very recently has this changed. However, some uncertainty still exists concerning the extent to which the bicycle can substitute for other modes of transportation in urban areas. This question is investigated by first observing the development of transportation in recent years in selected areas of the Federal Republic of Germany, in which use of the bicycle has been on the increase. This makes it possible to identify those changes in modal choice that have brought about this increase in the use of bicycles. The changes in modal split in favor of bicycles reflect individual reorientations that have led to substitution processes. Further potential of the bicycle as a substitute for other modes of transportation will depend on policymaking. Social scientific behavioral studies based on the concept of the situational approach make it possible to give reliable estimates of the order of magnitude of change to be expected and to predict the extent to which bicycles can become a substitute for private motor vehicles. (Author)