A Conjoint Analysis of Five Factors Influencing Heavy Vehicle Drivers Perceptions of Workload

Conjoint analysis, a multi-factor subjective scaling technique, was used in a study of heavy vehicle drivers to obtain a measure of their perceived workload demands under different driving conditions. These included combinations of low and high levels of traffic density, lighting, roadway type, visibility, and traction. A tradeoff comparison analysis was used to collect the conjoint scaling data from a subset of the complete 2−2−2−2−2 design. Results indicated that an additive factor representation fit the data very well, but that the five factors had very different importance weights. The drivers’ orderings of perceived demand appeared to be inversely related to their control over the conditions. The two most important factors (traction and visibility) are effectively environmental factors that cannot be easily controlled by the driver. The other three factors (traffic density, highway type, and lighting) can, at least to some extent, come under the control of the driver. Implications of these results and the use of conjoint scaling methodology are discussed.