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The power of two different theoretical frameworks, the theory of planned behaviour (expanded to include moral norm) and the driver behaviour questionnaire, to predict and explain drivers' speeding behaviour are compared and a combined model is suggested. One hundred and seventy-five test drivers, participating in a large-scale ISA-evaluation, answered a questionnaire in spring 2000. Based on the questionnaire data, logged speeding in autumn 2001 was predicted and LISREL-analysis was used for structural equation modelling. According to the results the two frameworks, alone or in combination, could explain between 38 and 53% of self-reported speeding and between 24 and 26% of logged speeding. A combination of the theory of planned behaviour and the driver behaviour questionnaire is presented and implications for the understanding of driver speed control are discussed.

Different systems of intelligent speed adaptation (ISA) have already been tested in the field and large-scale implementation is being discussed. But do we really know how these systems affect drivers during long-term use? Between 2000 and 2003 a total of 61 test drivers had an ISA speed-warning device installed in their vehicles. Data from these trials show that, initially, the device greatly reduced the amount of time the majority of test drivers spent above the speed limit, and to some extent also reduced their mean speeds, but this effect decreased with time. Further analyses of 27 of the 61 test drivers then showed that the activation of the warning system affected different drivers in quite a homogenous way, with regards to attitude, subjective norm and self-reported behaviour, but not with regards to perceived behavioural control. After activation, long-term use did, however, affect the test drivers in a homogenous way with regards to attitude, subjective norm and self-reported behaviour, as well as perceived behavioural control. When considering these results it must be remembered that the device tested was a first generation ISA speed-warning device and with more research we think that different ISA-systems could be improved and the effects made more stable during long-term use.