Evaluation of the driver's mental workload: a necessity in a perspective of in-vehicle system design for road safety improvement

Subjective measures of mental workload allow 'evaluation' rather than 'measurement', by establishing relative comparison between situations, and producing global and even "crude" criterion. Nevertheless, it is a powerful and easy to use tool, allowing detecting changes such as resource allocation that would be impossible to identify by direct observation. The methods of workload evaluation are diversified, with, nevertheless, a high infatuation for the subjective evaluation tool, and more specifically the NASA-TLX, with certainly a possible Matthew effect in addition to the willingness for the researchers to be congruent with the other studies conducted in the area. This paper discusses and debates upon the robustness, adaptation and reliability of existing tools, techniques and procedures for subjective mental workload evaluation such as the DALI for the driving context and the RALI for the riding context