Driver Task Load in Different Road Environments

Abstract

The research to be reported deals with the driver-environment interaction in terms of driver task load.

The potential significance of road environment in driver information processing follows from the fact that accident rates are different for different types of roads. Another relevant aspect is that task load experienced in a particular road environment appears to be a factor in driver route preference, a relationship of obvious relevance to traffic management.

We have investigated several road environments in terms of task load as indicated by psychophysiological variables measured while subjects drove an instrumented vehicle.

Experiment 1, employing 16 male Ss, concentrated on: (a) the .1 Hz component of the cardiac interval spectrum, and (b) the P₃₀₀ cortical potential component evoked by subsidiary stimuli. It was found that the motorway trajectory was associated with more load than either a city or a rural interlocal trajectory. I.e., the amplitude of the .1 Hz cardiac spectral component was lowest on the motorway, and P₃₀₀, was slower and its amplitude lower on the motorway. We replicated this study on different trajectories in Experiment II, again employing 16 male Ss, only to see the motorway section emerge as the outlier again. In Experiment III we returned to the motorway and rural interlocal trajectories of the first experiment. Catecholamine excretion rates over 1 hr driving periods were obtained for 8 male and 8 female Ss. The males showed the pattern of the first two experiments, their excretion rate being highest on the motorway, while the female Ss showed the opposite pattern.

These results emphasize that driving is not an open-loop, paced task. A particular environment does not ‘emit’ some fixed amount of load, but it sets an upper and a lower limit to that variable. Thus, the driving task is essentially self-paced, though its possible rate of self-pacing is constrained to different degrees in different road environments. The male drivers in our experiments assumedly seized the opportunity presented to them on the motorway, while female drivers drove in a more passive manner in that condition. This interpretation will be supported by additional analysis of the data, in particular of the relationship between parameters describing driving performance on the one hand and measures of task load on the other. Implications for the problem fields indicated above follow from these results.