Elsevier

Accident Analysis & Prevention

Volume 43, Issue 6, November 2011, Pages 2037-2046
Accident Analysis & Prevention

Driving performance impairments due to hypovigilance on monotonous roads

https://doi.org/10.1016/j.aap.2011.05.023Get rights and content

Abstract

Drivers’ ability to react to unpredictable events deteriorates when exposed to highly predictable and uneventful driving tasks. Highway design reduces the driving task mainly to a lane-keeping manoeuvre. Such a task is monotonous, providing little stimulation and this contributes to crashes due to inattention. Research has shown that driver’s hypovigilance can be assessed with EEG measurements and that driving performance is impaired during prolonged monotonous driving tasks. This paper aims to show that two dimensions of monotony – namely road design and road side variability – decrease vigilance and impair driving performance. This is the first study correlating hypovigilance and driver performance in varied monotonous conditions, particularly on a short time scale (a few seconds). We induced vigilance decrement as assessed with an EEG during a monotonous driving simulator experiment. Road monotony was varied through both road design and road side variability. The driver’s decrease in vigilance occurred due to both road design and road scenery monotony and almost independently of the driver’s sensation seeking level. Such impairment was also correlated to observable measurements from the driver, the car and the environment. During periods of hypovigilance, the driving performance impairment affected lane positioning, time to lane crossing, blink frequency, heart rate variability and non-specific electrodermal response rates. This work lays the foundation for the development of an in-vehicle device preventing hypovigilance crashes on monotonous roads.

Highlights

► Road design and road scenery impair alertness and driving performance. ► Driving performance can be used as surrogate for alertness. ► Countermeasures can focus on technological approaches using surrogate measures.

Introduction

Driving a car is one of the most common, though fairly dangerous, tasks in industrial countries. Road crashes are the main cause of premature death of people younger than 45. The burden of crashes is counted not only in lives, life handicaps but also as a cost to the society. The road toll in Australia in 2005 was 1 627 fatalities for an estimated social cost of AUS $15 billion (Australian Transport Safety Bureau, 2008). These figures are still of concern, though road safety interventions have improved the situation. Human errors contribute to around 90% of all crashes, and inattention to the forward roadway is often a contributing factor to crashes (Amditis et al., 2010). This suggests that the major effort to improve road safety should target countermeasures for driver inattention. However current measures focus mainly on safety devices, improvement of the road infrastructure, laws and regulations, but very little on human factors (Eoh et al., 2005). In Queensland inattention and fatigue (revealed in driver’s lapses in vigilance) contribute to 6% and 5% of fatal road crashes, respectively. Furthermore, inattention is the second contributing factor to all crash occurrences (12%) (Queensland Transport, 2005).

The driving task is complex and demanding and as a consequence, infrastructure authorities have attempted to simplify the driving task, for example through modifications to highways, while vehicle manufacturers have enhanced car design and equipment to improve comfort and safety (e.g. ABS, cruise control, power steering).

A consequence is that the driving task has been almost reduced to a lane-keeping task on highways and new types of crashes have emerged from these contemporary road safety interventions (Cerezuela et al., 2004). Drivers, particularly professional drivers, may suffer from the monotony of the driving task resulting in an increase in crash risk due to lapses of vigilance. It has been shown that if the driving task is highly predictable and uneventful then their ability to react to unpredictable events deteriorates (Thiffault and Bergeron, 2003b). Most fatigue crashes are recorded on roads of good quality, with few curvatures and which were supposedly designed to improve road safety (Fletcher et al., 2005, Thiffault and Bergeron, 2003b). This raises the question of the role of monotony of the driving task in explaining vigilance related crashes.

The concept of monotony is typically entangled in the research with fatigue and hypovigilance. Nevertheless Thiffault and Bergeron (2003b)’s experiment demonstrated that driver vigilance decrement as indexed by subjective and physiological measures is more frequent in a monotonous environment, such as highways and rural roads. It is also estimated that 27% of city drivers having reported fatigue related to a road crash or incident did not feel tired prior to the incident and 35% felt slightly tired. Most of these drivers were driving on well known, repetitive routes. This phenomenon appears even more on rural roads where 45% of drivers involved in crashes reported that they were not tired at all prior to the incident and where road geometry are highly monotonous (Fell and Black, 1997).

The aim of this study is to assess the effects of road monotony on driver vigilance and correlate it to impaired driving performance. This study focuses on two factors that decrease vigilance: (i) the road design (in terms of predictability) and (ii) the roadside environment (in terms of variability). An electroencephalograph (EEG) is used to monitor driver vigilance throughout a simulator experiment. The effects on vigilance decrement are then correlated to driving performance measurements.

In this experiment a simulated understimulating driving task was designed to isolate the effects of road monotony on driver vigilance. A driver simulator is used in order to ensure the safety of participants as well as control that participants are driving in the same conditions. This is done by creating four different road scenarios which enable all different combinations of high/low road design (geometry) and roadside variability. Road geometry is varied through the curvature of the road as well as its altitude. Roadside environment is varied through road signs, buildings and traffic frequency. Driving more than 30 min on monotonous roads has been shown to induce impairments similar to the one observed when fatigued. On the other hand fatigue due to time-on-task is observed after longer (more than 1 h) driving tasks Thiffault and Bergeron (2003b), Yamakoshi et al. (2009) and Eoh et al. (2005). In this study each driving scenario is a short driving task of approximately 40 min. This disentangles monotony effects and fatigue due to time-on-task. Such a design enables us first to isolate and quantify effects of road monotony on driver vigilance. Then vigilance levels are correlated with measurements from the driver, the car and the environment. Such knowledge can then be combined with appropriate mathematical models in order to provide accurate real-time estimates of driver vigilance on monotonous roads. Various mathematical models can be used and a range of promising approaches can be found in Larue et al. (2010)’s study modelling vigilance evolution during a short vigilance task.

Section snippets

Effects of monotonous driving on vigilance

Driving requires sustained vigilance, i.e. the ability to maintain sustained attention within the road environment (Thiffault and Bergeron, 2003b). A lack of visual, motor or cognitive stimuli can alter the ability to sustain vigilance. Drivers experience vigilance decrement more frequently in monotonous environments, especially when driving on highways at night. Monotony has a mainly psychological effect on the driver (Scerbo, 1998) through its effects on alertness and results in a vigilance

Participants

Twenty-five subjects, 7 males and 18 females aged between 18 and 49 (mean age = 29.1 years, S.D. = 8.3), volunteered to participate in this study. Participants were recruited from the Queensland University of Technology (10 students younger than 25 and 15 staff members older than 25). Participants had their licence for a minimum of two years, drove a minimum of three days a week and drove a minimum of 100 km a week. This is similar to previous research (Campagne et al., 2005) so that potential

Data analysis

Driver vigilance was assessed through analysis of data collected with the EEG. EEG data were collected at 7 different positions on the scalp (O1, O2, T5, T6, P3, P4 and F3) following the International 10–20 Electrode Placement System at 80 Hz and are divided into 1 s epochs. Epochs with too high/low values (threshold ±75 μV), linear trends, improbable data and/or abnormally distributed data were rejected. A 4-term Blackman-Harris window and a 0.5 Hz cut-off high-pass filter were also used to reduce

Data analysis

Episodes of reduced alertness and microsleeps – as assessed through the states presented in Section 4.1 – can be correlated to different measures (surrogate measures) obtained from sensors which can be used in real cars (see details in Section 2). All epochs of each participants are categorised into the vigilance levels described in the previous section. Values of surrogate measures are investigated by vigilance level in order to detect any correlation between the driving performance and the

Limitations

The research reported in this article features a number of limitations which should be acknowledged.

A relatively small number of participants is used in this experiment. However the sample size is statistically sufficient to study effects of monotony on a range of surrogate measures. Females and university students are over-represented in the samples used in this study. While the likely impact of such bias is unclear, it still represents a potential limitation. Nevertheless no statistical

Conclusion

The impact of monotony on driver vigilance has not been thoroughly studied, although it is an important factor contributing to crashes. This experiment shows that during a monotonous driving task two dimensions of monotony, namely the road design monotony and the roadside variability, can lead to a rapid decrement of the alertness of the driver. Such impairment is assessed with EEG analysis and is associated with increasing probabilities of alertness decrement and microsleeps as time increases.

Acknowledgements

The authors are indebted to Rebecca Michael, Sébastien Demmel and Renata Meuter for their help with the design and the collection of data used in this modelling study. The authors would also like to thank Mary Sheehan for initiating the research program on monotony.

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