Window tinting and night driving: A dual task investigation

Abstract

This study was designed to test the implications for night driving of a proposal put forward by a window tinting lobby group to reduce the required minimum visible light transmittance (VLT) of front side windows of cars from 70% to 35%. A sample of 24 young (aged under 30 years) and 24 elderly (aged 59 or over) subjects were required to complete target detection and reaction time tasks using peripheral vision. These tasks were performed both through a clear or tinted front side window and both in the presence and absence of a concurrent visual tracking task performed on a computer screen directly in front of the subject. The contrast value of the targets to be detected also took two different values. It was found that the elderly performed worse on the task overall, producing 178 of the 179 target detection failures in the study and also registering longer reaction times than the young group. Reaction times recorded for the elderly group were also found to be longer when they were required to view the targets through the tinted window. Similar effects were found for the elderly resulting from the dual task manipulation (longer reaction times when performing the concurrent task) and from the target contrast manipulation (longer reaction times when reacting to the low contrast target). As this study was very conservative in nature, it is concluded on the basis of significantly longer reaction times for the elderly subjects when looking through the tinted window that industry pressure to lower the minimum VLT of front side windows should be resisted and that these windows should be required to allow 70% of incident visual light to pass through to the eyes of the driver.