The objective of this study was to answer the following questions: How do the drivers experience Intelligent Speed Adaptation (ISA) - informative, compulsory and recording? How does ISA affect driving behaviour? What are the differences between the different types of ISA systems? In a field study 24 subjects drove the instrumented car with route guidance and ISA. Every subject drove the same route four times. The route included different types of traffic environment with different speed limits. The speed limits were 40, 60, 70 and 80 kilometres per hour and the environment varied from motorway to residential area. This paper discusses the study and its results.