Driver distraction: a review of the literature

Monash University Accident Research Centre - Report #206 - 2003

Authors: K. Young, M. Regan & M. Hammer

Abstract

This report provides a comprehensive review of the current research on driver distractions deriving from within the vehicle. The impact of technology (e.g., mobile phones and route guidance systems) and non technology-based distractions (e.g., eating, smoking and conversing with passengers) on driving performance is examined and the relative influence of these distractions on driving is discussed. Approximately one quarter of vehicle crashes in the United States are estimated to result from the driver being inattentive or distracted. Whilst the full extent to which distraction is a causal factor in vehicle crashes in Australia is not yet known, there is converging evidence that it likely to be a significant problem here. As more wireless communication, entertainment and driver assistance systems proliferate the vehicle market, the prevalence of distraction-related crashes here and overseas is expected to escalate. The various methods that have been employed to measure driver distraction are examined and those measurement techniques that appear most promising in being able to accurately measure in-vehicle distraction are identified. In the final section of the report, recommendations for research and for the management of driver distraction are provided as a first step in stimulating development of a national agenda for dealing with this issue.

Executive Summary

PURPOSE OF THIS REPORT

The purpose of this review, which was commissioned by Holden, is to examine the current literature on driver distraction, focussing specifically on in-vehicle distraction; that is, distraction caused by activities or objects inside the vehicle rather than those outside the vehicle.

The first section of the report discusses the impact of technology-based distractions (e.g., mobile phones, route navigation and email/internet) and non-technology-based distractions (e.g., conversing with passengers, eating/drinking and smoking) on driving performance. In the second half of the report, the various methods that have been used to measure distraction are described and the measurement techniques that appear most promising in being able to accurately measure in-vehicle distraction are identified. Future research needs and recommendations for minimising driver distraction are made in the final section of the report.

INTRODUCTION

Despite the complexities of the driving task, it is not unusual to see drivers engaged in various other activities while driving, including talking to passengers and listening to the radio and even reading. Preoccupation with electronic devices while driving is also becoming increasingly common. Any activity that distracts the driver or competes for their attention while driving has the potential to degrade driving performance and have serious consequences for road safety. Research by the National Highway Traffic Safety Administration (NHTSA) estimates that driver inattention in its various forms contributes to approximately 25 percent of police-reported crashes. Driver distraction is one form of driver inattention and is claimed to be a contributing factor in over half of inattention crashes (Stutts, Reinfurt, Staplin & Rodgman, 2001; Wang, Knipling & Goodman, 1996). However, as more wireless communication, entertainment and driver assistance systems proliferate the vehicle market, it is probable that the rate of distraction-related crashes will escalate (Stutts et al., 2001).

TECHNOLOGY AND NON TECHNOLOGY BASED DISTRACTION

Several in-vehicle devices and activities reviewed in this report appear to have the potential to distract the driver and significantly impair their driving performance and safety. The major findings to emerge from the reviewed literature are summarised below.

Mobile Phones

Many studies have found that using a hands-free phone while driving is no safer than using a hand-held phone. Using a mobile phone while driving can increase the risk of being involved in a collision by up to four times.
Research suggests that both the physical and cognitive distraction caused by using mobile phones while driving can significantly impair a driver's visual search patterns, reaction times, decision-making processes and their ability to maintain speed, throttle control and lateral position on the road.
Mobile phone use also often involves associated tasks that may further distract the driver. These activities can include writing down phone numbers on a piece of paper whilst driving or writing down dates or notes in diaries.
Sending a text message is more distracting than simply talking on a mobile phone.
Research has found that talking on a mobile phone is more distracting than holding an intelligent conversation with a passenger, but no more distracting than eating a cheeseburger.

Route Guidance Systems

Entering destination information is believed to be the most distracting task associated with the use of a route guidance system, however use of voice input technology can reduce the distraction associated with this task.
Route guidance systems that present navigation instructions using voice output are less distracting and more usable than those systems that present the information on a visual display.
Route guidance systems with voice recognition technology are a more ergonomic and safer option than systems that require visual-manual entry.
Route guidance systems that provide turn-by turn instructions, rather than presenting complex holistic route information, are less distracting to the driver and present the most useable means of navigation.

Email and Internet Facilities

Some researchers believe that speech-based email systems have the potential to distract drivers and undermine road safety. As a result, a growing number of system designers are recognising that speech-based systems are not a panacea for driver distraction and are focusing on developing alternative interfaces such as those that rely on tactile feedback.

Entertainment Systems

Tuning a radio while driving appears to have a detrimental effect on driving performance, particularly for inexperienced drivers.
Research suggests that simply listening to radio broadcasts while driving can impair driving performance.
Research suggests that operating a CD player while driving is more distracting than dialling a mobile phone and eating, however the use of voice-activation may minimise this distraction.

Non-Technology Distraction

A recent study revealed that a greater proportion of drivers involved in traffic accidents are distracted by eating or drinking (1.7%) than by talking on a mobile phone (1.5%). Another study corroborated this finding and found that eating a cheeseburger was as distracting as using a voice-activated dialling system, but less distracting than continuously operating a CD player.
Several studies have found that smoking while driving increases the risk of being involved in a crash.
A summary of current research on teenage passengers revealed that the presence of passengers increases crash risk, particularly for younger drivers, and this is believed to result largely from distraction and peer-pressure.

In summary, there is converging evidence that both technology-based and non-technology-based distractions can have a detrimental effect on human driving performance. The extent, however, to which distraction compromises safety is dependent on the frequency with which the driver is exposed to the source of distraction in question. Very little, if anything, is currently known in Australia (and indeed in most other countries) about the relative frequency with which technology and non-technology-based tasks are performed. The findings reported here do, nevertheless, provide important information that can be used to optimise the ergonomic design of the Human Machine Interface (HMI) in vehicle cockpits and inform the development of other countermeasures for minimising driver distraction.

RECOMMENDED DISTRACTION MEASUREMENT TECHNIQUES AND MEASURES

In addition to reviewing what is known about both technology and non-technology-based distractions deriving from within the vehicle, the authors reviewed the various scientific techniques which have been used to measure driver distraction and the measures of driving performance (e.g., lane keeping) which appear to be vulnerable to the different types of distraction. While this material was reviewed primarily to assist Holden, it is reported here to assist others undertaking distraction-related research. The following scientific techniques for measuring distraction were identified:

on-road and test track studies;
driving simulator studies;
dual-task studies;
eye glance monitoring studies;
the visual occlusion method;
the peripheral detection task; and
the 15 Second Rule.

The findings of this review suggest that using a range of distraction measurement techniques, rather than a single technique, would be appropriate in evaluating HMI design concepts and prototypes in vehicles. The particular technique, or sub-set of techniques, employed, however, will depend on the particular aspect of the HMI to be assessed, and in particular on the form of distraction (e.g., visual, physical etc) that is imposed on the driver by that aspect of the interface. With the possible exception of on-road and test track studies, and the 15-second rule, all of the above methods are considered suitable for use in HMI evaluation studies. On-road studies are more dangerous to conduct and are less experimentally controlled than simulator studies, and there is some doubt in the literature about the validity of the 15-second rule.

COUNTERMEASURES FOR MINIMISING DISTRACTION

Whilst the magnitude of distraction as a road safety problem in Australia is not yet fully known, there is converging evidence from studies overseas that it is likely to be a significant issue here and that it is likely to become a greater contributor to road trauma as the number of technology-based sources of distraction in vehicles increases. On the basis of the literature reviewed, the following recommendations are made for minimising the effects of driver distraction.

Research

A carefully designed study of the prevalence of driver involvement in distracting activities within the vehicle should be undertaken. This information, combined with the epidemiological data from the previously mentioned study being conducted by the University of Western Australia Department of Public health Injury Research Centre, will enable an initial assessment of the magnitude of the problem in Australia to be made. If driver distraction is shown to be a significant problem, then better recording by Police of the role of distraction in crashes will be needed.
An inventory of existing and emerging technologies and services which can be accessed on-board the vehicle or through portable devices carried into the vehicle should be compiled. From this, research is needed to develop a taxonomy of driver distractions that defines the different sources of distraction deriving from within the vehicle and categorises them according to how distracting they are in absolute and relative terms.
Research is required to better understand drivers' willingness to engage in potentially distracting tasks while driving, the factors that influence this willingness and under what conditions drivers engage in distracting tasks.
There is currently little knowledge regarding how drivers use in-vehicle technologies: whether they use them in the manner intended by the designer; and at what point (or threshold) and under what conditions they become a distraction.
Research needs to be conducted into whether and how individual difference factors such as age, gender, driving skill and experience influences the ease with which drivers are distracted.
To complement the above activities, research is needed to develop a taxonomy of distracting events and objects occurring outside the vehicle. As for sources of distraction deriving from within the vehicle, research is needed to quantify how distracting they are in absolute and relative terms, alone and in combination with internal distracters. Some research on this issue is being undertaken by the Monash University Accident Research Centre and this should be closely monitored.
There is a need to develop objective, standardised, measures of distraction in order to enable more accurate comparisons of results across studies (NHTSA, 2002a).
Further research is needed on alternative modes of input and output, such as tactile feedback and voice activation, to determine whether these interaction methods are a safe and viable alternative to manual entry systems.
The operation of certain on-board and portable technologies, such as mobile phones, often involves associated tasks such as writing down phone numbers and address details on pieces of paper. There is a need for research to design the HMI so that it eliminates as far as possible the need for these secondary tasks.
No research, to the knowledge of the authors, has examined the potentially distracting effects of portable devices used by pedestrians and other road users (e.g., mobile telephones, pedestrian navigators) to access information and services when negotiating their way by means other than driving through the road system.
The overall costs and benefits afforded by various technologies must be assessed before restricting or prohibiting drivers from engaging in distracting tasks while driving. Listening to a radio broadcast, for example, might be distracting: yet, for a truck driver, this activity might be beneficial in maintaining vigilance in a low workload driving environment.

Education and Training

A good deal is already known about the risks associated with engaging whilst driving in various distracting activities. It is important that these are brought to the attention of drivers and passengers. As a matter of priority, it is important to make the motoring public aware that hands-free mobile phones can be just as distracting as hand-held phones.
As with the use of mobile phones, drivers must be educated and trained in the optimal manner in which to interact with existing and emerging on-board technologies and services accessed through portable devices in order to minimise distraction.
Where flexibility exists in the manner in which these devices can be operated (there are, for example, many ways to tune and select a radio station), user manuals and tutorials provided by vehicle manufacturers and service providers should highlight the most ergonomic and least distracting methods for doing so.

Legislation and Enforcement

Existing legislation should be reviewed and, where necessary, new legislation created to limit driver exposure to, and deter drivers from engaging in, activities which have the potential to distract them. There is sufficient evidence, for example, to justify a ban on the use of hands-free phones whilst driving if this can be practically enforced by the Police.

Vehicle Design

The most effective way to minimise technology-based distraction is to design the Human Machine Interface (HMI) ergonomically. In Europe, North America and Japan, draft standards have already been developed which contain performance based goals which must be reached by the HMI so that the in-car technologies do not distract or visually entertain the driver while driving (e.g., the European Statement of Principles for Driver Interactions with Advanced In-vehicle Information and Communication systems). It is important that the development of these standards be closely monitored by relevant authorities in Australia and that local vehicle manufacturers and system developers are encouraged to refer to these standards in designing their systems.
The operation of certain devices including mobile phones and route guidance systems often involves associated tasks such as accessing written information, which can further distract the driver. There is a need for research to develop the HMI so that it eliminates the need for these associated tasks.

Licensing

Handbooks for learner and probationary drivers should draw attention to the potential risks associated with engaging in distracting activities within the vehicle.
Knowledge tests should include items pertaining to the relative risks associated with engaging in these activities.
Where appropriate, the graduated licensing system should be used to restrict driver exposure to distracting activities that are known to compromise safety. The findings presented here, for example, suggest that there is a case for restricting Probationary drivers from using (but not carrying) mobile phones while driving during some or all of the P-period.

Fortunately, we are at an early enough stage in the evolution of the vehicle cockpit to prevent distraction from escalating into a major road safety problem.

Sponsoring organisation: Holden Ltd.