MOBILE PHONE USE WHILST DRIVING:

PHONE OPERATION vs. VEHICLE TRANSMISSION Di Haigney l,3 and Ray.G. Taylor 2

Published 1998

1 Road Safety Dept. 2 Applied Psychology 3 Health and Safety Unit RoSPA Aston University Aston University 353 Bristol Road Aston Triangle Aston Triangle Birmingham Birmingham Birmingham B5 7ST B4 7ET B4 7ET A recent review of research investigating the potential effect of mobile phone use on a concurrent driving task, noted that not only were comparisons between handheld and hands-free operation confounded through critical shortfalls in experimental and statistical control, but also that only one study conducted in 1969 specified the use of a manual transmission vehicle (RoSPA, 1997). This paper details a series of controlled and wholly repeated measures studies, examining kinesthetic and cognitive interference resulting from handheld and hands-free mobile phone use whilst driving simulated vehicles with manual and automatic transmission. The concomitant effects on driving performance are discussed. Introduction Little agreement as to the potential effect of mobile phone use on driving performance is evident throughout the research literature (e.g. McKnight and McKnight, 1993; Bailey, 1994; Zwahlen, Adams and Schwartz, 1988; Briem and Hedman 1995; RoSPA, 1997b). Given the general observation that the use of phone units is indeed rising in all countries for whom connection data is available (RoSPA, 1997b; Violanti and Marshall, 1996), this apparent lack of consensus may well represent a matter of concern for ergonomists and driver behaviourists, as well as road safety practitioners. To an extent, the absence of clear data illustrates the complexity of assessing any association between mobile phone use, driver performance and accident likelihood - further exemplified and in effect compounding review, through the mutually exclusive application of and reference to particular methodologies across the research literature. Clear disparity in research emphasis may also be determined with cognitive or physical factors being tested as primary sources of interference (RoSPA, 1997b) and relatively few acknowledgements being made of any possible interaction between such factors or to attempts to assess such interactive effects (Brown, Tickner and Simmonds, 1969; Bailey, 1994). In addition, the research literature would appear to be vulnerable to a major source of confounding through a widespread failure to assess a common form of physical activity required during the driving task, onto which both physical and cognitive aspects of vehicular and phone operation may impact - the process of gear changing in a manual transmission vehicle. The present author was only able to determine one study which explicitly described the use of a vehicle fitted with manual gearshift against concurrent phone use (Brown et al., 1969).

It should be noted however, that as a number of studies have not stated the form of transmission fitted in their test vehicles (e.g. Wikman, Nieminen and Summala, 1998; Fairclough, Ashby, Ross and Parkes, 1991), it is not known whether an automatic or manual transmission vehicle was used throughout these experiments. Of those studies specifying transmission - the majority of the research literature - studies have been undertaken using automatic transmission vehicles, or in driving simulators or scenarios which mimic the operating conditions within an automatic vehicle (RoSPA, 1997b). The consideration of vehicular transmission type is of particular importance when considering potential conflict between the kinesthetic elements of simultaneous phone use, gear changing and other vehicular control behaviours. Furthermore, direct physical interference would appear to be maximised when driving a manual transmission vehicle and simultaneously using a hand held phone unit - a scenario particularly relevant to the existing situation in GB, given the substantial bias towards both manual transmission and hand held phone use during driving (RoSPA, 1997a; RoSPA, 1997b). In addition to the physical act of gear changing, differences in effective driver workload have been noted across transmission (Zeier, 1979) as well as across handheld and hands-free phone types (RoSPA, 1997b; Brookhuis, de Vries and Waard, 1991). It is possible therefore that performance across vehicular transmission types may also be further confounded with concurrent phone use by interference arising in the monitoring and decisional processes associated with the control over engine (and by extension, vehicular) speed, as well as being introduced through the form of cellular unit operation. The potential for driver distraction arising through the physical demands of phone unit operation should not therefore be assessed in isolation, but viewed against issues of cognitive interference including the process of vehicular control. Ethical and legal considerations prevent the maximisation of ecological validity in studies assessing the possible affects of phone use on driver performance conducted in GB through real-world, on-road driving tasks (RoSPA, 1997b). Therefore, in order to test the relative effect of physical and cognitive demands arising from vehicular transmission and phone type on driving performance, an established and validated driving simulator would need to be employed for such an experimental design. This paper details a study developed to assess the main and interactive affects of vehicular transmission and phone type on performance under controlled, simulated conditions. Method Participants Thirty people (13 male, 17 female) with a mean age of 26.93 years (SD: 3.06) took part in the study. Each participant had held a GB manual transmission driving licence for private and light goods vehicles (PLG) for at least one year (mean value 4.37 years; SD: 1.73). Difficulty was experienced when potential participants were assessed for possession of a GB PLG automatic transmission licence, which would restrict them to the use of automatic transmission vehicles alone. However in GB, drivers holding a full PLG manual transmission licence (as per the sample) are already fully qualified to drive PLG automatic transmission and so this was deemed an adequate gauge of basic driving skill for this experimental design (Hoyes, 1992; Zeier, 1979). It should also be noted that given the relative rarity of automatic vehicles throughout GB, participants could not readily be recruited who either currently owned and/or mostly used an automatic transmission vehicle.

Design The study comprised a wholly repeated measures 2x2x3 factorial design, in effect allowing for up to 360 matched cases as illustrated in Figure 1. Participants were required to receive and converse with an incoming call on handheld or hands-free mobile phone equipment (the factor phone') whilst continuing to drive in either a manual or automatic transmission set-up (the factor 'transmission'). Driving performance was assessed across the factor of 'period', i.e. prior to, during and following the call. The run order in which participants experienced 'transmission' and 'phone' factors was counterbalanced throughout the sample, although logically the order of the 'period' factor could not be so adjusted.

Apparatus The Aston Driving Simulator The Aston Driving Simulator (ADS) comprises an adjustable car scat, steering wheel and pedal controls, placed so as to mimic the conditions found within a Ford Sierra right hand drive vehicle. The 'windscreen view' is displayed on a 21" monitor placed in front of the participant, with the external view being placed above the graphical depiction of the 'dashboard'. The monitor displays a computer generated graphic image of a single lane carriageway and car bonnet with perspective incorporated in order to replicate the drivers view.

The output also includes a rear-view mirror placed at the top centre of the 'windscreen view, which displays in real-time objects and events occurring behind the users 'vehicle'. A speedometer (and optionally a revolution counter) are also displayed on the dashboard image. Participants are able to negotiate their way along the carriageway through the manipulation of appropriate vehicular controls in a closed loop simulated environment. The road is also populated with 'intelligent others' on either side of the carriageway, capable of overtaking the user and each other. The carriageway dynamic may be specified by the experimenter. Driving performance variables including acceleration, speed, braking, steering and 'following' (i.e. distance maintained behind a vehicle in front of the user in the left hand carriageway) are logged each half second. Changes in experimental condition (e.g. transmission or phone factors) would be displayed on the monitor prior to the commencement of that particular experimental run. Experimenters initiated each condition in response to the participants indicating that they understood the task requirements and were ready to proceed. When operating as under an automatic transmission, participants are only required to use the brake pedal, the accelerator pedal and the steering wheel in order to manoeuvre the simulated vehicle in the ADS environment. The revolution counter is not displayed on the 'dashboard view'. When operating as under a manual transmission, participants are required to use the brake, accelerator, clutch, gear lever and steering wheel in order to manoeuvre the vehicle in the ADS environment. Participants use the clutch and gear lever (arranged as a 'straight H', 4 geared box [Zeier 1979: 8001 placed as per the specification for GB manual transmission Ford Sierras) in conjunction in order to travel up and down gears. Both visual and auditory feedback is available to participants to assist in the timing of gear changes, through the inclusion of the revolution counter on the screen as well as a simulated engine noise rising in pitch with engine revolutions per minute. Pop-ups As the ADS is currently only able to show a single carriageway with no intersections, this particular revision of the base programme included 'pop-ups', intended to mimic vehicles pulling out into the carriageway (Stein, Parseghian and Allen, 1991:184; Nilsson and Alm, 1991). The 'pop-up' vehicles took the appearance of other traffic and after pulling onto the carriageway travelled along it as an 'intelligent other'. The 'pop-up' vehicles spontaneously appeared on either carriageway, at a distance between 50 to 80 metres in front of the users vehicle (subject to a rectangular probability distribution) and at random along the right-hand carriageway. The simulated others already travelling along the carriageway would allow for 'pop-ups' by braking, or attempting to overtake - a decision based on an algorithm concerning the simulated others speed and relative distance from the 'pop-up' when it appeared, as well as the relative position and speed of the user. Mobile Phone Equipment In order to optimise face validity where possible, 'off-the-shelf cellular phone equipment was utilised (Zwahlen, 1988: 183).

A Nokia 1611 GSM cellular telephone was used across the handheld conditions, a model of phone which includes the keypad on the receiver, on the same face as the output speaker and input receiver mechanisms. An LCD display on the mobile phone displayed any numbers depressed on the keypad and the telephone number of any incoming calls. When operating as a handheld phone, calls must be 'received' through the depression of a specific push-button on the keypad and the unit held against the car for the duration of the conversation. In order to 'end' a call, another specific push-button on the keypad is depressed. The phone was located to the left of the steering wheel, in line with the gear lever and on a level with the dashboard readout dials. The phone was placed upright in the 'holster' provided with the unit on purchase. Subjects were required to return the phone unit to the holster following each 'conversation'. A compatible Vodaphone 'hands-free conversion kit' was also used for the hands-free conditions. The hands-free equipment comprised an earpiece speaker and microphone to be attached to the participants clothing. Subjects were still required to 'receive' and 'end' calls as per the handheld condition, although since the incoming and outgoing audio signals were relayed through the earpiece and microphone, the phone unit did not need to be removed from its holster. Secondary Task The secondary task was developed from the 'grammatical reasoning test' detailed by Baddeley (1968), used previously to replicate the demands of a conversation held over a mobile phone whilst driving a manual transmission vehicle (Brown, 1969). In Baddley (1968) two letters were presented to subjects either aurally or visually, followed by a statement concerning the order of the letters so presented. Subjects were required to respond to the statement by stating that it was either 'true' or false', allowing the subjects responses to be assessed against the actual presentation of material. Given that Baddley (1968) was intended simply to replicate the demands of verbal comprehension and that mobile phone conversations may be considerably more 'intense' and 'complex' than other conversations (Fairclough et al., 1994), the task has been adapted accordingly. The secondary task in this study includes the presentation of 5 stimulus letters, followed by a statement regarding the relative ordering of two of those letters in the series. Participants are required to state whether the statement on the previous series is 'true' or 'false' and are marked according to their response. A complete listing of the task items are included in Appendix X. Heart Rate Participant heart rate was assessed throughout the study via electrodes placed on the neck connected to a computer storing the data via biometric software. Heart rate data was uploaded against ADS performance data during data analysis. Biodata Questionnaire Prior to experiencing either the practice or experimental runs on the ADS, participants were required to complete a short form listing items relating to age, gender, driving experience and exposure, as well as experience of handfree and handhold mobile phones. Procedure On recruitment, participants were briefed as to the general design of the study and were required to complete a short biodata questionnaire.

Participants were sat in the ADS, adjusted the positioning of the seating until comfortable and were fitted with the electrode, earpiece and microphone. The operation of the mobile phone equipment was demonstrated - namely accepting an incoming call and ending the phone connection when the phone was in either handheld or hands-free mode. Participants were also shown how to operate the ADS in either transmission mode and were required demonstrate to the experimenter an understanding of both the phone and ADS controls. A practice period then followed, in which participants experienced each combination of phone and transmission factors for the same duration as for the experimental runs. The practice was followed by an interval in which participants were able clarify any remaining issues with experimenters if they so wished and then proceeded onto the experimental conditions when they indicated that they were ready to do so. Results and discussion Overview of biodata Although the small sample size precluded any real control over the performance variables through driving, overall mobile phone as well as concurrent driving and phone use experience, a summary of biodata collected has nevertheless been included for information in Table 1, as an illustrative and suggested model for future biodata considerations in studies examining driving performance and concurrent phone use.

Effects of transmission or phone type on driving performance The relative influence of transmission and phone type was tested across all performance variables within each experimental period, e.g. the effects of manual and automatic transmission were evaluated against handheld and hands-free phone operation within the period 'prior-to-call'. Those performance variables for which an effect could be derived at the 5% level via repeated measures ANOVA are listed below in Table 2 against experimental period.

Table 2. Main and interactive effects of transmission/phone on driving

performance, per experimental period

None of the performance variables were found to have a statistically significant main effect off phone type at the 5% level and heart rate alone evidenced a interactive effect of transmission x phone within the ‘during call’ period (df=1; f=4.53; p<0.042).

Figure 2 shows that the range evidenced in heart rate is more exaggerated in the automatic than in the manual transmission condition, possibly reflecting the greater apparent differential in task demands between handheld and hands-free operation in this condition. In terms of gross physical differences in operation, the left hand in the manual condition would regularly need to be removed from the steering wheel for gear changing. This is in contrast to the automatic condition in which the left hand need only be taken from the steering wheel in order to operate the phone unit.

This is supported in part, through data suggesting that the effect of phone type shows greater physiological mobilisation for handheld conditions (where the subject was required to hold the phone to their car throughout the conversation whilst driving, introducing greater physical interference) than hands-free (where subjects were only required to operate a push-button to receive the call and another to end the call) especially for automatic conditions. Table 2 shows that transmission appeared to exhibit the most widespread effect across performance variables throughout the study, with mean acceleration being significant across transmission for all three experimental periods.

It is noteworthy that significantly greater values of mean acceleration, detailed in figure 3, have been recorded in manual relative to the automatic transmission condition for all experimental periods - potentially a result of subjects overestimating the level of engine revolutions required for travel across the gears. The relative magnitude of mean acceleration values per experimental period are also the same across all conditions, being highest ‘pre-call’ and lowest 'following' the phone task - excepting manual transmission with handheld phone use. In this condition, mean acceleration values are greatest 'during' the call. It has been previously suggested that this may well be a consequence of the greatest direct physical interference occurring in this condition, with resultant cognitive overloading affecting the judgement of relative velocities and the use of the accelerator pedal (Brown et al., 1969). Table 2 also records that mean following (mean distance in metres from another vehicle in front of the user, in the left-hand lane) exhibits a main effect across transmission in the 'during call' period.

Figure 4 shows considerable disparity between mean following distances adopted across transmission conditions, with greatest mean following distances being noted in the manual conditions - findings somewhat at variance with prior assumptions (RoSPA, 1997b) and research literature when taken alongside other performance variables (see below; refer to figure 8). Although the effect of phone was not statistically significant, it is nevertheless of interest to note the opposing tendencies for mean following across phone conditions by transmission. Effect of phone use on driving performance Statistically significant differences in mean values for performance variables across the experimental periods of 'prior-to-call', 'during call' and 'following call' were tested for in each factor combination, via repeated measures ANOVA.

Table 3 shows that across all performance variables only SD speed (figure 5), SD acceleration (figure 6) and mean heart rate (figure 7) varied to a statistically significant degree (p<0.05) across all transmission and phone conditions.

SD speed and SD acceleration have previously been taken as representing ‘risk acceptance’ behaviours (Wagenaar and Reason, 1990; Matthews, Dorn and Glendon, 1991). Authors have suggested that a decrease in such behaviours may represent a concomitant response to a perceived increase in subjective risk, with participants attempting to moderate the level of their perceived exposure to risk contingencies (Haigney, Hoyes, Glendon, and Taylor, 1995; Haigney, 1999).

Given this framework, the 'risk acceptance' behaviours of SD speed and SD acceleration would appear to be minimised across all transmission and phone conditions within the 'during call' period, possibly indicating greatest subjective risk - assuming a direct and linear link between subjective risk perception and behavioural response (Haigney, 1999). It should also be noted that other researchers establishing a decrease in SD speed and acceleration throughout the duration of a polychronic phone task by drivers, argue that regardless of the possible relationship between subjective perception and speed deviation, an increased likelihood of vehicular collision occurs throughout this period relative to other traffic (Nilsson and Aim, 1991; Bailey, 1994) due to suppressed and delayed response to the behaviour of other vehicles.

Statistically significant variation across experimental period for all conditions was noted for mean heart rate at the 5% level, indicating increased physiological mobilisation throughout the 'during the call' period (Zeier, 1979). Such increased arousal, when assessed against the 'cautionary' downward shifts in SD speed and SD acceleration throughout this period may indicate that an increased level of workload is being experienced by participants attempting to drive whilst using a phone. This finding is consistent with other studies to date (Alm and Nilsson, 1990; Brookhuis et al., 1991).

Figure 8 shows a statistically significant (p<0.05) reduction in mean following distance 'during the call' period for all transmission and phone factor combinations, excepting manual transmission with handheld phone type. Previously, authors have argued that a reduction in headway may be associated with a strategy through which drivers are able to maintain speed and effective task workload when some other aspect of the driving task would require increased cognitive effort and processing in order to maintain performance (Haigney et al., 1997; Haigney, 1999).

Given the heart rate data, which suggests raised workload during the phone task, this hypothesis would appear to have some basis - although it is unclear why the manual transmission/handheld phone condition did not evidence any systematic shift in following behaviour, or why the automatic transmission conditions evidenced lower headway overall (refer also to figure 4). When reduced headway is considered against reduced responsiveness to traffic conditions as discussed above however (Nilsson and Alm, op. cit.; Bailey, op. cit.; Brookhuis et al., 1991; figures 5 and 6) it follows that the probability of collision with the leading vehicle is increased. Secondary Task Performance No significant differences (p<0.05) in secondary task performance were noted across any of the experimental conditions when tested via Friedman one-way ANOVA (df=3; Chi-square=0.61; p=0.894). Given the reliable shifts in primary task performance across period and the fact that the secondary task has been shown to be a valid, reliable and sensitive means for assessing driver workload (Brown et al., 1969), it could appear that participants were altering their driving patterns as a means of maintaining their ability to converse clearly and accurately throughout the phone task. It is of interest to note that the automatic transmission, hands-free condition presumed to represent the lowest workload for the driver (RoSPA, 1997b) was not only associated with the lowest levels of mean heart rate, but also the greatest mean number of correct responses to the secondary task. In contrast however, the manual transmission, handheld phone condition was not associated with the highest mean heart rate or the greatest mean level of error on the secondary task (these were both evidenced in the automatic transmission, handheld condition). The reason for this is cannot immediately be determined from study data.

Summary This pilot study has been designed to account for a range of critical failings identified in the studies performed in this area to date (RoSPA, 1997b). Through the analysis of the initial datasets, it would appear that the investigation and description of the relationship between car transmission, phone type and driver performance would appear to be more complex than anticipated, with assumptions regarding driver workload, transmission and phone type requiring further development. Data produced by this pilot pro-forma study indicates underlying mediating factors which have not yet been isolated through study design - at the very least this study demonstrates that cognitive and physical factors of polychronic phone use by drivers cannot readily be separated at the gross level (through transmission and phone type) and may well exhibit a more interactive dynamic than previously considered in the literature (RoSPA, 1997b). As a result, broadly held, populist assumptions regarding the relative pros of hands-free over hands-free phone units - especially with regard to probable accident likelihood - cannot be supported. All vehicle transmission and phone types in all possible combinations evidenced significant fluctuation in driver performance and workload in ways which strongly suggested increased accident likelihood - possibly simply to maintain phone task performance - even when participants were specifically instructed to attend primarily to the driving task. It is recognised that further research is required to test issues raised within this paper, as well as greater sample N to enable the biodata fields to serve as covariates within this pro-forma design. With the analyses available however, it would appear that phone use whilst driving leads to variation in driver behaviours which are strongly associated with subjective risk manipulation and accident involvement especially when considered against indices of driver distraction and workload. Whilst the emergency use of mobile phones is recognised as a significant benefit, the position stated in RoSPA (1997b) is maintained - namely that such calls do not need to made whilst actively engaged in the driving task - and that it can only be recommended that drivers do not engage in polychronic phone use.

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