Assessing the impacts and benefits of in-car route guidance advice via field trials

Field trials are conducted for a wide variety of reasons. Some of their objectives are met quite simply with little recourse to the collection and analysis of data. Other objectives, notably those relating to the evaluation of the net benefits of a full scale scheme, can be very demanding of data and can be seen to be beset by great methodological difficulties. Sophisticated analyses using appropriately specified models are seen as a solution to some of these problems. But if the models are to command confidence, it is essential that the next generation of field trials be designed to produce more information on user response than has hitherto been the case.