ISA effect assessment : from driving behaviour to traffic flow.

This paper discusses two complementary methods for ISA effect assessment, and how to apply them in a coherent manner. The first level consists of the effects on individual driving behaviour, typically measured with an instrumented vehicle or a driving simulator. Results at this level form the starting point for the second level, which consists of microscopic traffic flow simulation. ISA system characteristics and behavioural effects should be incorporated in the traffic simulation model. The main focus of the paper is on an explorative case study, in which the MIXIC model was applied to study the effects of a dynamic ISA system. The ISA penetration level was varied as an independent variable. The in-car control unit consisted of a mandatory ISA. The road configuration that was studied consisted of a lane drop from 3 to 2 lanes, and the roadside part of the ISA system determined the actual ISA speed limit based on the traffic state. The driver model was adjusted to take into account the set speed of the in-car ISA system, but otherwise, no strategic changes in driving behaviour were assumed. Results show a decrease in throughput (volume) combined with positive effects on safety (shock waves, speed variance) when ISA is introduced. For the validation of these results more research into the driver's behaviour in the presence of ISA is recommendable. For the covering abstract see ITRD E123876.