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Speed is related to safety on our roads, speeding may make cities or neighbourhoods unliveable, and speeding affects the environment. Therefore measures need to be taken to reduce speed and speeding. No single measure will solve all of the problems related to speed and speeding. Rather it takes a combination of measures including comprehensive infrastructure, credible speed limits, education, information, enforcement, vehicles, and vehicle technologies. Speed management measures rest on three pillars (the driver, the environment, and the vehicles) to intervene and to improve road safety. Through speed management, actions can be taken within three pillars, allowing for an effective ‘policy mix’ approach. Speed management policies can only be successful if people are willing to support or to accept these measures. One of the technological measures to reduce speeding or to help to maintain the speed is Intelligent Speed Assistance (ISA).

During the last two decades a lot of research on ISA has been carried out. Several trials with different types of ISA have shown that ISA can be an efficient and effective way to reduce speed and speeding and therefore, to have a positive effect on traffic safety. ISA is also expected to have a positive effect on fuel consumption, emissions, dust, and noise.

A trial with a supportive intervening ISA, installed in 34 cars & 3 buses, was conducted in the city of Ghent, Belgium. Comparison of logged speed data during the activation period and speed data after this period showed that ISA had a lasting effect on speeding. Effects were highest in the 90 kph zone, where speeding decreased by almost 10%. At lower speed limits the effects were smaller although speeding was more frequent. In the 30 kph zone, speeding decreased from 45.9% to 42.8%. This means that the counter pressure on the gas pedal was overridden in a vast amount of distance. Differences between drivers were, however, large. Speeding with the system varied between 3% and 50%. For most drivers, speeding was reduced with the system.

When questioning basic attitudes using surveys, most of the drivers did not report that driving fast is fun, liberating or exciting, before, during, or after the project. Most drivers stated that speeding is dangerous, reckless, and not sportive. Driving with ISA changed their behaviour on speeding: during the project, most of the drivers reported that they never drove faster on highways, outside urban areas, in urban areas, and in 30-zones. The drivers used the system voluntarily on highways and outside urban areas, which gave a first indication of their acceptance of the active accelerator pedal. They also experienced the pedal as satisfying and useful.

It was reported that ISA could have benefits in road safety and may even open new debates about speed policies. Still, one of the main questions was how the general public would evaluate these new devices and how they could be convinced to accept new legislation in relation to ITS and ISA. These questions led us to the major topic of this dissertation: the acceptability of ISA.

It was recognized that knowledge concerning the level of acceptance or acceptability of a measure is important for future implementation of in-vehicle technologies. Debates are continuing, but ironically, a clear definition of what acceptance and acceptability imply and how they should be measured is still lacking. We made a distinction between acceptance and acceptability based on the amount of time and the amount of experience the individual had with the system. While acceptance follows from beliefs and attitudes based on behavioural reactions after the introduction of a measure, acceptability is a prospective judgement, based on attitudes and beliefs about a measure before its introduction.

Based on different socio-psychological theories and data derived from ISA trials, we arrived at 14 relevant indicators that were divided into general indicators (related to persons’ psyches, social values, and norms at that time, etc.) and device-specific indications (factors that are directly related to the device itself). These 14 indicators were presented to randomly selected respondents (through Internet media) in a test survey. The main goal of this survey was to find out whether the distilled indications and the questions were indeed relevant, and whether some relationships could be found between the indicators. Through the use of factor analysis, we found out that our questions were relevant for every item, and some correlations were found between the items. It was also noted that some indicators would directly influence the acceptability of ISA, while some would influence others indirectly. This first step in our

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research enabled us to conduct a large-scale survey among the general public in the Netherlands and Belgium regarding the acceptance and acceptability of ISA.

In total, 7528 drivers responded to the questionnaire call by the two main interest groups in both countries; 5599 responses were found sufficiently complete to take into account for further analyses. The average respondent was male between 45 and 54 years old with a relatively high education and no children living at home. Their vehicle was the main mode of transport and on average they drove between 10 000 and 25 000 km/year. 76% of the drivers had been involved in an accident at least once, 11% of them had had an accident with injuries, 4% had had a severe accidents and 1% had been in an accident with casualties.

The resulting general indicators in the survey showed that the drivers had positive opinions concerning the current posted speed limits. The drivers would generally drive within the speed limit in urban areas. However, in 30 kph-zones they would speed more often. These results are in line with the Belgian, Dutch, and Swedish ISA-trials.

The respondents stated that behavioural aspects are a greater cause of accidents than contextual issues. The drivers were relatively positive about the use of ITS to support their driving behaviour. Already in 2004, the SARTRE research project indicated that drivers rated the use of certain ITS applications as positive, although they had only a few systems to choose from (GPS, ISA, alcohol-lock, driving monitor). In our study, the ratings for these systems were even higher. This might be an indication that drivers would like to have even more support when driving.

Almost 95% of the respondents in our survey stated that they are in favour of some type of ISA-system. In many studies, effectiveness was found as a relevant criterion to determine acceptability. However there is a difference in peoples’ opinion about the effectiveness and the effectiveness results found in trials. In our study, open systems were considered the most effective ones, although from a safety point of view (semi)-closed systems are considered better.

Closed ISA was more preferred (i.e. was found more satisfying and useful) than supportive ISA. This remarkable result might be explained by the fact that it was more difficult for the respondents to understand how the supportive systems actually worked in practice.

Although the support for ISA is relatively high, the respondents indicated that it was not unconditional. The more the implemented system would be perceived to intervene in their control of the driving experience, the higher the penetration level should be. The respondents of our study felt that young and professional drivers (especially trucks and buses) should have a more intervening system. This was also stated in other trial reports; however, in our survey many respondents also stated that ISA would be beneficial for all drivers. As in many ISA- studies the implementation of restrictive ISA was considered a good solution to stop frequent speeders. Our study also indicated that incentives would increase the support for more intervening systems. However, it would still be difficult to get people to accept restrictive ISA.

Finally, a model was estimated by using structural equation modelling (SEM) to find out which predefined indicators would be relevant to define the acceptability of ISA. Background factors, contextual issues and ISA-device related factors were used as indicators to predict the

level of acceptability. The factors that were used in the model were based on the methods used in past ISA trials, acceptance theories and models.

The four variables that had the largest total effect on the acceptability of ISA were (1) the effectiveness of ISA, (2) equity, (3) effectiveness of ITS, and (4) personal and social aims (4). Effectiveness was found a relevant predictor for acceptance in many trials (Morsink et al, 2006). In some studies the willingness to pay was reported to be a good predictor for acceptability. However, in our model the effect of willingness to pay was very low or even absent. Hence, it may be assumed that our model had better indicators than the willingness to pay.

With respect to context indicators, ‘personal and social aims’ seemed to be the variable with the highest influence on acceptability. Drivers, who rate social aims over personal aims with respect to speed and speeding, are more inclined to accept ISA. Personal and social aims had a high influence on most of the device specific indicators as well. Furthermore, drivers who speed for their personal benefit were found to rather speed more often. Drivers who speed in high-speed zones would also be less inclined to accept ISA.