Karel Brookhuis

The use of psychophysiology to assess driver status

Twenty subjects completed an on-the-road driving experiment, consisting of two different tests conducted on two separate days. A two-part test was administered while subjects were under the influence of alcohol (BAC < = 0.05%); a four-part test was administered without alcohol consisting of a 2.5 h driving test under vigilance conditions on a quiet highway. The order of the tests was balanced across subjects. Changes in relevant physiological parameters, such as ECG and EEG, reflected changes in driver status and predicted driving impairment. Impairment of driving performance was measured in a standard driving test (SD lateral position and SD steering wheel movements) and in a recently developed car-following test (reaction to speed changes of a leading car).

Behavioural adaptation to driving with an adaptive cruise control (ACC)

Abstract The present paper describes a study that aims at assessment of driver behaviour in response to new technology, particularly Adaptive Cruise Control Systems (ACCs), as a function of driving style. In this study possible benefits and drawbacks of Adaptive Cruise Control Systems (ACCs) were assessed by having participants drive in a simulator. The four groups of participants taking part differed on reported driving styles concerning Speed (driving fast) and Focus (the ability to ignore distractions), and drove in ways which were consistent with these opinions. The results show behavioural adaptation with an ACC in terms of higher speed, smaller minimum time headway and larger brake force. Driving style group made little difference to these behavioural adaptations. Most drivers evaluated the ACC system very positively, but the undesirable behavioural adaptations observed should encourage caution about the potential safety of such systems.

MEASURING DRIVING PERFORMANCE BY CAR-FOLLOWING IN TRAFFIC

The measurement of impairing effects on driving performance by such external factors as alcohol, medicinal drugs, or mobile telephoning, etc., is extended with a new test. Most existing methods of measuring impairing effects in the actual driving environment have the drawback that, irrespective of high sensitivity, they measure driving skills that are involved in only a very low percentage of accident causes, i.e., accidents after motor-response or eye-hand co-ordination errors. Since in accident causation, attention and perception errors predominate over response errors, on-road studies should examine specifically deterioration in attention and perception. The ability to follow a car in front, as measured by coherence and reaction time to speed variations, offers such a measure of attention and perception performance.

State of science: mental workload in ergonomics

Mental workload (MWL) is one of the most widely used concepts in ergonomics and human factors and represents a topic of increasing importance. Since modern technology in many working environments imposes ever more cognitive demands upon operators while physical demands diminish, understanding how MWL impinges on performance is increasingly critical. Yet, MWL is also one of the most nebulous concepts, with numerous definitions and dimensions associated with it. Moreover, MWL research has had a tendency to focus on complex, often safety-critical systems (e.g. transport, process control). Here we provide a general overview of the current state of affairs regarding the understanding, measurement and application of MWL in the design of complex systems over the last three decades. We conclude by discussing contemporary challenges for applied research, such as the interaction between cognitive workload and physical workload, and the quantification of workload ‘redlines’ which specify when operators are approaching or exceeding their performance tolerances. Practitioner Summary: The study of workload in ergonomics has risen in popularity since the 1980s. Applied problems, particularly in transport, have taken centre stage in recent years. New developments in neuroergonomics measurement techniques offer promise in quantifying both the interaction of physical and mental workload, as well as the elusive ‘redline’ performance limit for overload.

ASSESSING DRIVER STATUS - A DEMONSTRATION EXPERIMENT ON THE ROAD

Twenty subjects completed an on-the-road experiment that consisted of two parts on two separate days. One was a one-hour driving test under the influence of alcohol (BAC less than = 0.05%), the second a two-and-a-half-hour driving test under vigilance conditions. Impairment of driving performance was measured in a car-following test as well as in a standard driving test. Changes in relevant physiological parameters, such as ECG and EEG, reflected changes in driver status and predicted driving performance impairment.

CRITERIA FOR DRIVER IMPAIRMENT

Most traffic accidents can be attributed to driver impairment, e.g. inattention, fatigue, intoxication, etc. It is now technically feasible to monitor and diagnose driver behaviour with respect to impairment with the aid of a limited number of in-vehicle sensors. However, a valid framework for the evaluation of driver impairment is still lacking. To provide an acceptable definition of driver impairment, a method to assess absolute and relative criteria was proposed to fulfil the paradoxical goal of defining impaired driving which is consistent yet adaptable to interindividual differences.

LATE POSITIVE COMPONENTS AND STIMULUS EVALUATION TIME

The amplitude and latency of late positive components were, together with reaction time (RT), studied in a task which combines visual and memory search. The visual display contained either one, two or four letters, as did the memory set. Six load combinations, resulting in one, four, eight and 16 comparisons, were examined. The reaction time data indicated a self-terminating search process. Three late positive components were present in the evoked potential: one at 375 msec after the onset of the display, one at 375 msec after the offset of the display and one around 600 msec. Only the latter component appeared to be sensitive to the number of comparisons. Adaptive averaging was applied to this latter component. The latency of this P300 suggested, in contrast to the RT data, an exhaustive search process. In addition there was a negligible correlation between the response latency and P300 latency at single trial level. Several hypotheses are suggested for what P300 could have to tell us.

Limiting speed, towards an intelligent speed adapter (ISA)

This study concerns the effects of a prototype intelligent speed adapter (ISA) on speeding in actual traffic. Twenty-four subjects were included in a test of effects of feedback on speed behaviour, mental workload and acceptance. Subjects drove an instrumented vehicle in normal traffic on various types of roads with different speed restrictions. Subjects completed the test route twice, half of the subjects received specific feedback in the second trial (experimental group), half of the subjects did not (control group). The groups differed in several ways, the most important being adaptation of their behaviour after feedback. Subjects in the experimental group behaved more according to traffic rules, in particular speed limits, than subjects in the control group. No significant differences in workload were found. Two types of feedback were tested to acceptance and were rated differently.

Effect of road layout and road environment on driving performance, drivers' physiology and road appreciation

Infrastructural changes were implemented on rural 80 km/h roads in The Netherlands in an effort to reduce speeding. The road infrastructure changes were designed to produce discomfort for the speeding driver by providing noxious auditory and haptic feedback. On experimental roads, smooth-surface road width was reduced by using blocks of gravel chippings placed along the centre line and at intervals on road edges. It was predicted that these changes would increase mental load while driving, and thereby decrease speeding. In a field experiment 28 subjects drove an instrumented vehicle over experimental and control roads. A decrease in driving speed and swerving behaviour was found on the experimental roads, and this was coupled with a decrease in heart rate variability, consistent with an increase in mental load. Roads in two different road-side environments (woodland vs. moorland) were also tested. There were differences in driver appraisal of the two environments, but no interactions were observed between these appraisals and driving performance on the experimental roads. It is concluded that the infrastructural measures have a useful role to play in road safety through a reduction in driver speeding.

A COMPARISON OF DIFFERENT WAYS TO APPROXIMATE TIME-TO-LINE CROSSING (TLC) DURING CAR DRIVING

Three experiments are presented in which the accuracy of different methods to approximate time-to-line crossing is assessed the first experiment TLC was computed, using a trigonometric method, during normal driving while the vehicle stayed in lane. The minima of TLC were compared with two approximations and it was found computing TLC as lateral distance divided by lateral velocity gave poor results. It was concluded that this simple approximation is not suitable for measuring TLC minima in studies of driver behaviour. A way of computing TLC that takes account of the curved path of the vehicle resulted in a good fit of TLC minima. In two other experiments the vehicle exceeded the lane boundary, either intentionally as a result of a lane change manoeuvre, or unintentionally as a result of impaired driving. In these cases no TLC minima exists since these only occur as a result of correcting steering actions to stay within the lane. In contrast to normal lane keeping, it was found that prior to crossing the lane boundary, the simple approximation resulted in more accurate estimation of available time before the lane boundary is exceeded compared to the more complex approximation. This indicates that for lane keeping support systems and systems that detect when the driver has fallen asleep and drifts out of lane, a simple algorithm for TLC estimation may give reliable results, while this algorithm is not accurate enough for more fundamental studies of driver behaviour. However, the reliability of the approximation is only satisfactory over a very short time range before the lane boundary is actual exceeded. This may result in warnings that come too late and result in too little time to respond for the driver.