Rijkswaterstaat from the Dutch Ministry of Transport, Public Works and Water Management needs knowledge in the area of workload in car driving. This report is the result of a second project phase, in which we investigated how traffic volume, road lighting, and a cognitively loading secondary task influenced driving behaviour and workload. In an experiment, subjects drove a fixed route in an instrumented vehicle on a motorway, on which the public lighting was experimentally manipulated. We started the measurements at the beginning of the evening, yielding runs in busy as well as in quiet traffic conditions. In half of the runs, the subjects also had to perform a cognitively loading secondary task. During the runs we registered the driving behaviour as well as a number of physiological variables (heartbeats and eye blinks). After each run, subjects completed a questionnaire that measured the subjective rating of mental effort. We expected the workload to be higher in dense traffic, on an unlit road, and while executing the secondary task. We found effects of traffic flow conditions and of the secondary task on speed choice, in the physiological measures, and in the subjective ratings. When conducting the secondary task, subjects carried out fewer overtaking manoeuvres. Motorway lighting especially influenced the steering reversal rate, the eye blink frequency, and the steering effort. We found changes in behaviour due to a secondary task and to traffic volume, but we practically found no changes in behaviour due to roadway lighting. The latter is in contrast to the Phase 1 results, where participants e.g. reduced their speed on an unlit road. High traffic volume yields a higher workload, but the additional workload effect of lighting is relatively minute. Effects of lighting that we found can be measured within a vehicle-driver system, but not by using loop detectors or similar roadway data acquisition systems. On the other hand, factors that can be measured in the traffic flow are not suitable to quantify workload effects of roadway lighting. Therefore, we must conclude that designing new, workload-based, switching schedules for roadway lighting is not feasible. (Author/publisher)
Abstract