The aim of the present study was to investigate the impact of two-up driving on driver fatigue by comparing it to the major operational alternative, single driving. A between-subjects design was used, in which 15 single drivers and 22 two-up drivers drove a regular type of trip over a selected route. The route selected was Perth to Broome and return which covered approximately 4,500 km and took in the vicinity of 100 hours to complete. This route is typical of driving in remote zones and was one familiar to most of the participants. The range of fatigue measures used for the evaluation were identical to those used for a previous evaluation of staged driving. In brief, these included subjective measures, measures of physiological state, measures of cognitive performance off road and on-road measures of driving performance.
The results showed that irrespective of operation, fatigue increased for drivers on a long trip typical of remote zone driving. Performance, physiological arousal and subjective fatigue measures tended to converge - self-reported fatigue was associated with poorer performance and reduced arousal.
While, overall, the two-up group showed greater fatigue compared to single drivers, some ways of doing two-up were less fatiguing than single driving. Important differences in the organisation of the trips for two-up drivers were found in terms of trip length and the distribution of rest obtained across the trip. Striking differences were seen in recovery and maintenance of alertness associated with these operational distinctions among two-up drivers. Overnight stationary rest for two-up drivers at the time of peak fatigue, at mid trip, was associated with a dramatic reduction in fatigue levels after the break, and allowed these drivers to finish the trip with the lowest levels of fatigue of any group, including single drivers. Two-up drivers who had no significant stationary rest, but had the shortest trip duration of any group showed minimal recovery at mid trip but showed an overall increase in alertness over the homeward journey, finishing the trip at pre-trip levels of fatigue. These drivers also fared better than single drivers. Among single drivers, substantial recovery of alertness was seen after the stationary rest at mid point, but this recovery was not maintained with decreases in alertness evident at the end of the trip. In contrast, two-up drivers who did much longer trips, and did these trips without the benefit of stationary rest, showed no recovery at mid trip and continued to deteriorate, ending the trip more tired than any other group.
The present results also highlighted the importance of chronic fatigue as a hazard for long distance drivers. Chronic fatigue accumulated before the start of the trip had a clear impact on the development of fatigue during the trip. For two-up drivers, fatigue at the beginning of the trip was clearly influenced by the amount of work they did in the ten or so hours before starting to drive, such that they started the trip more tired than single drivers. Moreover, this disadvantage remained for most of the trip, irrespective of two-up trip type, but was particularly evident over the first leg of the trip where fatigue for two-up drivers continued to worsen at a greater rate than for single drivers. In other words, where fatigue had accumulated before the start of the trip (from activities other than driving) clearly added to the build-up of fatigue due to driving once the trip had started.
Compelling evidence for the impact of chronic fatigue was also provided by analysis of changes in the effectiveness of breaks taken by drivers as the trip progressed. As a whole, two-up drivers appeared to gain less from breaks than did single drivers but the influence of work practices among two-up drivers critically influenced the utility of breaks. As two-up trips became longer, breaks became increasingly ineffective in the latter part of the trip, and totally lost their effectiveness towards the end of the trip. It seems that these drivers simply became too tired for breaks to be of any use. Breaks were most useful for the two-up group which had a long overnight stop in Broome. This group showed better response to breaks than single drivers and also better than two-up drivers who only went as far as Broome but had no overnight rest. Thus, where the work practices kept fatigue under control, such as on shorter two-up trips and two-up trips including overnight rest, breaks were more likely to be helpful. In contrast, on trips where fatigue was allowed to build-up, such as on single trips and the two-up trips going beyond Broome, breaks did not provide relief once fatigue had accumulated.
Taken together the findings of this study suggest that judicious use of effective rest (that is, night rest) in combination with two-up driving may be the best strategy to manage fatigue on very long trips such as these. The results also underscore that the most effective improvements in managing fatigue must take account of overall work practices, including activities in the past week, activities before driving begins as well as the way the trip is structured.
Type: Research and Analysis Report
Sub Type: Consultant Report
Author(s): AM Feyer, A Williamson & R Friswell
Topics: Fatigue, Heavy vehicle
Publication Date: 01/12/94