Driver mental workload requirements on horizontal curves based on occluded vision test measurements

Abstract

This thesis documents an evaluation of driver mental workload requirements on horizontal curves based on occluded vision test measurements. Driver workload is an important concept in the design of highway systems. A successful highway design requires that the workload capabilities of a driver are not exceeded or under utilized. A vision occlusion apparatus was used to examine driver workload on and around horizontal curves. Data were collected by using a computerized vision occlusion apparatus to limit the visual input of individual test subjects. The objective of the occluded vision tests was to measure the mental workload associated with two parameters of horizontal curvature: degree of curvature and deflection angle. Two types of statistical testing were used in this analysis: two factor ANOVA with replication, and linear regression. The ANOVA tests were used to test for significant differences in the mean driver workload among the levels of the independent variables: degree of curvature and deflection angle. After the statistically significant variables were determined, regression analysis was performed to estimate the quantitative relationship between workload and the geometric parameters of horizontal curves: degree of curvature and deflection angle. The vision occlusion test method was found to be sensitive to changes in driver workload values on horizontal curves. The results of the testing indicate that as degree of curvature increases, the workload level on a driver increases. The test results also show that there is not a statistically significant difference in workload for the majority of deflection angles. The results also indicate that as a driver approaches a horizontal curve, there is a point where the driver will begin to prepare mentally for the increased workload caused by the horizontal curve. Drivers prepare themselves by increasing their workload operating level to match the workload created by the horizontal curve.