Free public transport: a trigger for modal shift?

Congestion has grown to be more and more of a problem in and around cities. The last two decades, car use has increased enormously and if no action is taken, we will soon all be standing still. Consequently, sustainable mobility has become an important issue and policy makers introduce several measures in an attempt to tackle the rising mobility problems. One course of action is trying to make public transport more attractive to car users, in order to create a modal shift from private towards public transport.
Because of the way it is organised, public transport is very suitable for regular and repeating trips made to and from (big) cities, in other words, for commuting. Although most commuters have this useful transport mode at their disposal, several of them do not make use of it. In Belgium, data from the National Institute of Statistics reveals that 72% uses the car for their commuting trips. For Brussels, being a major area of employment and very well served by public transport, only 63% are using their car. But is there still a margin for a further modal shift? What are the obstacles that need to be overcome in order to make public transport more attractive? What are the advantages of public transport according to the commuters and how can they be exploited? And more extreme, can free public transport be the solution to shift people to public transport?
In Belgium, several cities have been experimenting with free public transport based on the concept of a third payer system. This implies that the price of public transport is not paid by the user or provider, but partially or completely by a third party, such as local authorities, other public organizations and private organizations. But is price the key factor in the transportation mode decisions? Or are there other important factors that influence people their travel behavior? Research among students being able to travel for free in Brussels has already shown that free public transport alone is not enough to reduce congestion (De Witte et al., 2006). In this paper, we further explored this question for commuters by means of a large scale survey.