The effects of increased workload on driving performance and visual behaviour

Abstract

The workload of drivers has been increasing in modern times due to the growing use of In-Vehicle systems. The higher task demand resulting from these extra visual and auditory
stimuli presents an increasingly challenging problem for drivers, and has become a growing safety concern, as the higher workloads can adversely affect driving performance and must be balanced against the benefits from in-vehicle systems. Existing models suggest that when the induced workload is relatively low, drivers can deal with this increased demand by using different coping strategies; however, when the workload increases above a certain level, drivers’ performance decreases. These models are relatively simplistic and do not describe the extent to which drivers’ coping strategies can impact on the relationship between workload and performance, which are difficult to observe by traditional measures. The literature suggests that visual behaviour or eye movements, with its physiological nature, combines attributes of both attention state and human behaviour, and can be used to provide sensitive, diagnostic, and instantaneous measurements to investigate the impact of increased workload on performance, and explore associated coping strategies. An on-road experiment was therefore conducted to observe drivers’ behaviour when their workload was increased by in-vehicle secondary tasks, and the impact this had on their performance, using eye movement as well as traditional vehicle control and manoeuvring measurements. The field experiment was run under two driving scenarios of Car-Following and Free-Driving, on two road sections in Hampshire over a period of three months, using the Transportation Research Group’s Instrumented Vehicle (IV) and a FaceLabTM eye monitoring system. An Operation Simulation System was developed for drivers to perform a series of in-vehicle auditory and visual tasks through touch screen and audio systems, which reflected two different types of workload (i.e. mental and visual), with three levels of difficulty. Surveys were also conducted during and after each test run to assess drivers’ workload perception and gain an understanding of their experiences of performing the tasks, and a database established to organise all the information collected to enable subsequent analyses to be conducted readily. The results show that drivers’ behaviour was significantly impacted by additional tasks, and their secondary task performance decreased steadily with task complexity. The effects were consistent across the two Scenarios, although driving performance generally deteriorated more for the visual tasks than auditory ones, which reflects the higher conflict of visual and manual resource caused by these tasks, and all drivers took action to compensate either by increasing their headways in Car-Following, or reducing their speed in Free-Driving. The effects were reflected in their visual behaviour, which showed higher blink rates and shrunk visual searching range for the auditory tasks, i.e. a higher mental workload over baseline driving, and higher saccade and more visual transactions between different objects for the visual ones. Differences were also found in the driving and visual behaviour of individual driver characteristics groups, including gender and different experience groups. While traditional performance measurements showed many differences in behaviour due to the extra in-vehicle tasks, the different coping strategies adopted by drivers were typically observed only through the analysis of their visual behaviour. The use of these additional measurements provides an improvement to existing models for describing the relationship between workload and performance in dual-tasking.

More information

Identifiers

Catalogue record

Export record