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Dynamic driver workload assessment and its implications for highway design and operations Musa, Patrick Tamba

Abstract

Design standard manuals and road safety guidelines are all formulated with safety as the main cornerstone, but road mishaps have continued to occur with the dare consequences of loss of life and serious injury. Research has shown that a large proportion of these mishaps can be attributed to the driver, thereby increasing the need for the application of human factors in road design. It is now generally accepted that to build safer roads, design should reflect the behaviour and the characteristics of the driver. Research in this area has identified design practices that tend to overload the information processing capacity of the driver as the main cause for concern. These practices often lead to high mental workload and subsequent driving errors. The engineer therefore needs to predict driver workload in order to design and operate a road system that will accommodate the information processing capability of the driver. This research proposed a driver workload model that combines road complexity and operating speed in a time constraint approach to workload. The model was tested in an experiment on a test track consisting of curves of various radii, interspersed with tangents. Twenty four (24) drivers drove the test track in an instrumented car, at speeds ranging from 30km/hr to 100km/hr, as well as speeds mimicking driving scenarios adopted by late and leisure drivers. The workload experienced by drivers was measured using a secondary task technique of random number repetition. Amongst other things, the results showed that whilst satisfying their motives, drivers aspire to optimum workload levels which are governed by their speed management strategies, and that by modelling these strategies, design workload limits can be determined. In the experiment, late drivers adopted a speed management strategy that limited the demand on their attention (workload) to 80%. Leisure drivers had an attention demand limit of 45%, whilst the 85th percentile driver on the road showed a limit of about 50%. The above limits were used to evaluate the experimental test track. The results were comparable to those from the accepted geometric design consistency evaluation criteria.

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