The development of in-car speed assistance makes it possible to help drivers to choose an appropriate speed, complying with the legal speed limits. This functionality is expected to become increasingly important in speed management if integrated well with more traditional speed management measures. Based on state-of-the-art scientific literature, this paper describes the effects of Intelligent Speed Assistance (ISA) and Advanced Cruise Control (ACC), two systems that directly affect speed behavior. The direct effects on speed are described as well as derived effects on safety, traffic efficiency and the environment. The expected safety effects of the various ISA types are most promising, although it is not clear yet when and to what extent the expectations can become reality.
The current evaluations of in-car speed assistance systems are mainly based on simulations, as these systems have not at all or have barely been implemented in real traffic. Reported studies on ISA and ACC include different methodologies and data collection techniques varying from field operational tests (FOT), (single) instrumented vehicle experiments, driving simulator studies, to traffic simulations. These studies were conducted in a number of countries, including the United Kingdom, Finland, the Netherlands, Sweden, Denmark, and Australia.
The role of in-car speed assistance systems can gradually become more prominent in speed management, in combination with traditional measures (infrastructural engineering, education, enforcement). Both ISA and ACC directly affect speed, while other systems such as vision enhancement and black boxes, are considered to have an indirect effect on speed, which was barely addressed separately in research so far. For all types of ISA, promising effects are predicted, particularly regarding safety. Automatic controlling ISA is most effective, but at the same time has the lowest driver acceptance. A lack of user acceptance along with, for instance, possible legal problems can impede a large scale implementation of this ISA type.
When all vehicles are equipped, mandatory dynamic automatic controlling ISA could reduce fuel consumption and harmful emissions by 4 to 11 percent.
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