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Postural support strategies of disabled drivers and the effectiveness of postural support aids
ARTICLE IN PRESS
Applied Ergonomics 39 (2008) 47–55 www.elsevier.com/locate/apergo
Postural support strategies of disabled drivers and the effectiveness of postural support aids Clare Lawtona,, Sharon Cooka, Andrew Maya, Keith Clemob, Susan Brownc a
Ergonomics and Safety Research Institute, Loughborough University, Loughborough LE11 3UZ, UK Motor Industry Research Association (MIRA), Watling Street, Nuneaton, Warwickshire CV10 OUT, UK c Derby Assistive Technology Evaluation Centre, Derby City Hospital, Uttoxeter Road, Derby DE22 3NE, UK b
Received 16 March 2006; accepted 11 March 2007
Abstract The paper discusses a series of driving trials that were conducted to investigate postural stability of disabled drivers and to assess the effectiveness of a representative sample of support aids. Twenty-three disabled drivers with varying levels of physical disability and seven non disabled drivers participated in the study. The test car was equipped with transducers to measure vehicle velocity and acceleration (longitudinal and lateral), steering wheel movement and torque, and the bracing forces exerted by the driver on the steering wheel. Video cameras were installed to record postural support strategies and displacement of the driver and to record deviation of the car from the specified path. Subjective data regarding driver attitudes and acceptance were also collected through the administration of questionnaires. Findings from the study showed that support aids significantly improved driving performance and reduced physical exertion to maintain an upright driving position for disabled drivers. However, ergonomics design aspects regarding the ease of use and acceptance of the support aids by the end users were identified as obstacles to their sustained use in everyday driving. r 2007 Elsevier Ltd. All rights reserved. Keywords: Disabled; Drivers; Posture
1. Introduction Although someone may be well balanced when sitting in a static environment, things change when driving. Driving is a very dynamic task which imposes lateral and longitudinal forces on the driver which will throw most people out of balance. The driver must be able to compensate for these forces and return to a safe, upright position without losing hand placement or inadvertently moving the wrong controls. Drivers often subconsciously brace themselves within the vehicle whilst driving to maintain an upright position or make small adjustments to their posture after a particular manoveuer (Andreoni et al., 2002; Reed et al., 2000; Coelho and Dahlman, 1997). However, for drivers who have a physical disability resulting in impaired balance or reduced upper body strength, or have reduced lower limb function for example, these compensatory actions Corresponding author. Tel.: +44 1509 226900; fax:+44 1509 226960.
E-mail address: [email protected] (C. Lawton). 0003-6870/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.apergo.2007.03.005
may be difficult to achieve. This may affect the operation of controls and have a resultant impact on safety. Haslegrave (1986) states that there is currently insufficient knowledge of the extent and causes of disabled driver accidents and incidents and that further research is required. Twenty years on, data are still very limited. Although incident and accident data are few, research does indicate that driving a car adapted for a disabled person is far more laborious and fatiguing for a person with a physical disability. Disabled drivers often experience additional physical demands, i.e. forces required to activate adapted controls such as conversion of the accelerator and brake from foot to hand operation, conversion from hand steering to foot steering, and relocation of the minor controls (Peters, 2001; Haslegrave, 1989). Reducing the energy required to maintain an upright driving position is important for disabled drivers as this will help maximise driving comfort, duration and safety. To gain a stable driving position disabled drivers are first encouraged to use their original car seat. However, standard car seats having
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sufficient adjustment options tend to be available only in the top of the range models. Consequently, products have been developed that can be added to any standard car seat to provide improved support (postural support aids). 2. Study aims The aims of the study were to investigate whether postural stability is an issue of concern for disabled drivers and to assess the effectiveness of support aids that are currently available.
journey resulting in awkward and inefficient postures. Awkward postures when sustained for prolonged periods of time will increase muscular loads and increase the likelihood of fatigue and perceived levels of discomfort (Park et al., 2002; Silverstein, 1995). Fatigue is a particularly important consideration for disabled drivers with spinal cord injury as the risk of spastic cramps increases with increasing load and tiredness. 4. Method 4.1. Overview
3. The driving environment for disabled drivers 3.1. Seating Many disabled people will sit on a cushion to improve their comfort while driving, because they are short in stature and/or to prevent pressure sores (Murray-Leslie, 1990). However, the addition of seat cushions may increase driver instability (Coopers, 1986). The use of smooth seating surfaces that are aimed at easing ingress and egress to the vehicle may also further reduce postural stability, increasing the likelihood of gross changes in posture. 3.2. Number of contact/bracing points In addition to the seat itself, the seat in combination with the steering wheel and vehicle body components (window edges, etc.) can act to provide a supportive framework. However, certain vehicle control adaptations can reduce the number of contact points available, for example when the driver must steer with one hand whilst using a hand accelerator/brake control arrangement. Points of contact may also be lost for amputees and where a driver has suffered loss of sensation in part of the body. The loss of those bracing points may increase the physical demands placed on other body parts as they act to compensate. 3.3. Making the vehicle fit the driver The layout of controls may not be ideal for all drivers with a disability due to the great variation in anthropometric dimensions of disabled drivers. To compensate for potential limitations/misfit of control adaptations disabled drivers often adjust seating features to gain functionality rather than support and comfort (Cornwell, 1985). 3.4. Physical effort and fatigue Disabled drivers may already be exposed to high physical demands in terms of strength and effort, resulting from either the adaptation to their car controls or simply overcoming the physical constraints of their disability (Peters, 2001). In addition, initial instability may lead to progressive deterioration of driving position during the
The study consists of two parts: a set of exploratory structured telephone interviews and a series of driving trials. The driving trials were conducted to verify findings from the interviews and to assess, in more detail, postural support strategies engaged whilst driving and the effectiveness of a range of support aids in terms of improving driver comfort, physical effort and driving performance. 4.2. Participants 4.2.1. Structured interviews Telephone questionnaires were conducted with 58 disabled drivers and 17 non-disabled drivers. A larger sample of disabled participants was actively sort to account for greater variation in anthropometric dimensions and physical capabilities of the disabled driver population. Table 1 shows the medical conditions of disabled respondents. 4.2.2. Driving trials Driving trials were conducted with 23 disabled and 7 non-disabled participants. Again to account for greater variation in the disabled driver population a larger sample than non-disabled drivers participated in the study to provide a more representative sample. Participants for the driving trials were randomly selected from respondents to the telephone interviews that had stated an interest in participating further in the study. Participants were required to be 17 years and above, hold a current driving
Table 1 Medical conditions of respondents to the questionnaire Medical condition and the number of respondents Arachoditis (n ¼ 1), arthritis (n ¼ 6), artificial limb (n ¼ 1), broken back (n ¼ 1), broken coccyx and fibromyaligia (n ¼ 1), cerebral palsy (n ¼ 2), cerebral palsy and quadriplegia (n ¼ 1), congenital lower limb deformity (n ¼ 1), degrading spine (n ¼ 3), faulty knee replacement (n ¼ 1), fused spine (n ¼ 1), MS (n ¼ 6), muscular dystrophy (n ¼ 1), nerve disease and spinal injury (n ¼ 1), Not specified (n ¼ 2), paralysis of left leg (n ¼ 1), paraplegia (n ¼ 5), paraplegia and MS (n ¼ 1), polio (n ¼ 5), short arms (n ¼ 1), spastic diaplegic-paralysis (n ¼ 1), spondylitis (n ¼ 1), stroke (n ¼ 5), TB and hip double replacement (n ¼ 1), tendons cut in left knee (n ¼ 1), tetraplegia (n ¼ 6), tumour in spine (n ¼ 1), weak legs (n ¼ 1).
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licence and where appropriate have a physical impairment or disability. The aim was to include participants with a range of disabilities including stroke and high spinal lesions. The participants’ ages ranged from 23 to 84 years, with a mean age of 53 years. Of the disabled driver participants, 20 people used a wheelchair. All participants who used a wheelchair transferred into vehicles and drove from a standard car seat. The numbers of participants within each medical diagnosis group were low, as shown in Table 2. Results from the telephone questionnaire indicated the need to conduct an analysis based on physical ability reflected in the type of controls/adaptations used in the vehicle rather than medical condition per se. Therefore, for analysis purposes participants were grouped based on the types of vehicle controls/adaptations used. Although not a set standard, this method enabled a consistent means of categorising participants into workable subgroups. The aim of this base level of categorisation was to enable identification of patterns between these broad subgroups and the data collected during the trials. Due to small numbers in some of the categories, analysis was limited to the three larger groups consisting of more than four participants; these are italicized in Table 3. 4.3. Methods 4.3.1. Structured interviews The telephone interviews probed issues relating to postural stability, these included information regarding driving tasks/manoeuvres, type of vehicle driven, type of
Table 2 Medical conditions of disabled drivers participating in the driving trials Medical condition and number of participants
vehicle controls, duration of journey times, use of additional support, whether discomfort was experienced, whether postural changes occurred. The interview was also used to recruit people to participate in the driving trials. 4.3.2. Driving trials A 2000 model year Renault Megane Scenic Automatic was used. For drivers using adapted controls, suitable adaptations were fitted (Table 3). The test vehicle was fitted with Setra 2g and Endevco 2g accelerometers to measure lateral and longitudinal accelerations, respectively. Vehicle speed was measured using a Datron microwave speed sensor. Any disturbance of the driver’s position resulting from vehicle acceleration was recorded using two video cameras that were fitted inside the vehicle to record images from two different perspectives (side-on and overhead view) of the driver. The extent of deviation from the upright position could then be observed and matched to particular driving tasks. In order to assess the amount of bracing during the manoeuvres, the forces and moments exerted by the driver on the steering wheel were measured. A steering wheel with four spokes was fitted (Fig. 1). Each spoke was fitted with strain gauges to measure the force parallel to the steering column axis. An additional transducer (a steering wheel force load cell (FTSS Child dummy neck transducer)) and a MIRA steering potentiometer was fitted between the steering wheel and column to measure steering wheel movement/angle (control input) and steering torque. All data were filtered and amplified by an ASTECH 16 PIX, Programmable Signal Conditioning Unit and subsequently digitised and recorded using a DAQBOOK Series 200 Analog to Digital Converter. Digitised signals were analysed using Diadem software on a standard PC. Two techniques for assessing a driver’s lateral (steering) control were devised. The first technique used the standard
Archoditis and nerve disease and spinal (n ¼ 1), arthritis (n ¼ 2), cerebral palsy (n ¼ 1), cerebral palsy and quadriplegia (n ¼ 1), congenital lower limb deformity (n ¼ 1), faulty knee replacement (n ¼ 1), fused spine (n ¼ 1), MS (n ¼ 2), muscular dystrophy (n ¼ 1), paraplegia (n ¼ 2), polio (n ¼ 3), short arms (n ¼ 1), spastic diaplegia-paralysis from L1 (n ¼ 1), stroke (n ¼ 1), TB and double hip replacement (n ¼ 1), tetraplegia (n ¼ 3).
Table 3 The number of disabled participants and type of vehicle controls Steering controls
Brake/ accelerator controls
Standard foot controls
Adapted to hand controls
Standard steering wheel
Spinner attached to the steering wheel
12 (7 nondisabled and 5 disabled participants) 1
4
49
13 Fig. 1. Interior view of the test vehicle.
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deviation of steering angle when the car was negotiating the turns. The second technique consisted of asking the driver to steer so as to maintain as accurately as possible the outside edge of the front right-hand tyre with the left-hand edge of a white line painted on the road surface. The car was fitted with a transverse scale extending from the right front corner of the car. A video camera mounted above this and looking downwards continuously filmed the intersection of the white line on the scale (Fig. 2). This was later analysed to measure the deviation of the car from its intended path. The measurements of braking accuracy were also taken using the same video camera and scale. In addition to the objective performance data described above, subjective data relating to the drivers’ reported accounts of their experiences and impressions of driving with the supports and any bracing strategies were recorded using a series of rating scales and open-ended questions. 4.3.3. Procedure The driving trials consisted of: driving round a figure of eight circuit (to investigate the effects of lateral acceleration), ascending and descending a steep hill and braking on the descent (to investigate the effects of longitudinal acceleration and deceleration). The first and last driving sessions were conducted in the standard car seat, without
the addition of any support aids. All other sessions were conducted with the addition of progressive levels of postural support (referred to as Trials A–F, Table 4). Each trial required the completion of three consecutive circuits of the figure of eight course which was marked out by a white line on the tarmac and three consecutive ascents and descents of the hill. For the first two circuits, a target speed was suggested of 16 km/h (10 mph), then 24 km/h (15 mph) whilst for the third circuit the subject was invited to drive at the maximum speed they felt they could confidently maintain. 4.3.4. Performance measures The mean speeds attained by each participant when cornering the left and right bends in the third circuit of the figure of eight tasks were used as a performance indicator (the third circuit had no set speed and was determined by the participant). The standard deviation of steering angle during each cornering was also calculated to provide a measure of driving accuracy. After each driving session, a series of rating scales were used to capture data of ratings of perceived exertion (Borg, 1998), driver confidence, perceived ease of use, comfort and bracing points. 4.4. Selection of support aids A comprehensive market review of support aids was undertaken. Support aids were grouped by generic characteristics and were split into three categories, aids that provided: lateral support to the pelvis, lateral support to the trunk and longitudinal support to the trunk. A representative support aid was selected from each category to be used in the trials. Selected support aids included: a pelvic support belt that was designed to provide lateral support to the pelvis, a Thoracic support that provided lateral support to the trunk, and a shoulder harness that was designed to provide longitudinal support to the trunk (Fig. 3). The effectiveness of these aids was assessed in the driving trials when they were used in isolation and in combination with one another.
Fig. 2. Aerial view of transverse scale extending from the right front corner of the test vehicle.
Table 4 Support aids used in Trail sessions A to F Pelvis support A B C D E F
No support aids | | | | No support aids
Thoracic support
Shoulder harness
| |
| | Fig. 3. Selected postural support aids.
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5. Results 5.1. Telephone questionnaire—reported postural difficulties Fifty-eight disabled drivers and 17 non-disabled drivers were interviewed. Results from the telephone interviews found that postural stability is an issue for a high percentage of disabled drivers that responded. Thirty-eight of disabled drivers interviewed (66%) reported the need to stabilise or brace themselves against something whilst driving. Furthermore, although bracing occurred for a high percentage of disabled drivers they still reported that large postural changes occurred from which they could not then right themselves into an upright driving position. The predominant postural change reported was the propensity to end up leaning to one side reported by 24 disabled drivers (41%). In comparison, only two of the non-disabled drivers reported changes in posture and both stated they were able to easily right themselves. None of the nondisabled drivers reported any problems in maintaining an upright driving position while driving. 5.2. Driving trials
Percentage of participant group
5.2.1. Postural support behaviours when no support aids present There was a significant difference in the number of bracing points used by non-disabled and disabled drivers (U ¼ 37, p ¼ 0.035). Results from the driving trials found that when no support aids were present, six out of seven (86%) of non disabled drivers reported using 0 or 1 location for bracing, whereas disabled drivers reported using 1–4 different bracing locations. Disabled participants that drove using hand controls for acceleration and braking and steered using a spinner (enabling one handed steering) reported using a higher number of different
bracing points than other disabled drivers, with 7 out of the 13 (54%) reporting using two or more different bracing points (Fig. 4). Areas within the vehicle that participants braced concurred with observations made from the video footage and varied depending on the type of controls people used. The seat back and the central consol were used for bracing by three out of the four drivers (75%) using ‘steering with spinner and standard foot controls’ (disabled participants with restricted upper limb function). Whereas the majority of participants that used a spinner in combination with hand controls (slightly restricted upper limb and greatly restricted lower limbs) (8 out of 13, 61.5%) relied on the arm rest in the door for bracing. 5.2.2. Postural support behaviours when support aids present For all participants (non-disabled and disabled drivers) the need to brace decreased as more support aids were used. For disabled drivers, the combined use of the pelvic support and shoulder harness (Trials session D, Fig. 5) reduced the need for bracing for a large percentage of disabled participants (65%), with only 8 out of 23 (35%) bracing themselves against something within the vehicle when wearing these aids, compared to 20 out of 23 (85%) when no support aids were present (A and F). For nondisabled drivers, the pelvic support and thoracic support (Trial session C) reduced the need for bracing for six out of seven (85%), with only one out of 7 (14%) of this group needing to brace themselves when wearing these aids compared to 5 out of seven (71%) when no support aids were used. 5.2.3. Driving performance There were no significant differences between driving performance of the disabled and non disabled participants in terms of speed and driving accuracy in the trial sessions when no support aids were present (A and F). All of the
100% 90%
8% (n=1)
14% (n=1)
25% (n=1)
15% (n=2)
25% (n=1)3
1% (n=4)
40% (n=2)
80% 70% 60%
2 bracing points
40% 60% (n=3)
30% 10%
4 bracing points 3 bracing points
57% (n=4)
50%
20%
51
23% (n=3)
1 bracing point
50% (n=2)
29% (n=2)
23% (n=3)
0 bracing points
0% Standard steering Standard steering wheel and wheel and standard foot standard foot control (non control (disabled) disabled)
Steering with spinner and standard foot controls
Steering with spinnerand hand controls
Participants groups based on vehicle controls Fig. 4. Percentage of each respondent group (based on type of vehicle controls) and the number of bracing points used in Trial session A (no support aids present).
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100 Percentage of participants
90 80
n=20
Non disabled participants
n=19 n=5
70
Disabled participants
n=14
n=4
60 50
n=3
n=3
40
n=20
n=8
n=3 n=9
30 20
n=1
10 0 No support aids 1
A
Pelvic support Pelvic support Pelvic support Pelvic and Thoracic and Shoulder support, support harness Thoracicand Shoulder harness B
C
D
E
No support aids 2
F
Trial session (support aids used) Fig. 5. Percentage of participants that reported bracing themselves during the trial sessions.
support aids were found to have a positive affect on driving performance for both the non-disabled and disabled drivers. Speed, driving accuracy, My moment (the moments about the vertical axis of the steering wheel), number of bracing points, and driver confidence were all significantly improved when compared to the no support aids present trial sessions (A and F). Support aid combinations used in Trial sessions C (pelvic and thoracic support) and E (pelvic, thoracic support and shoulder harness) provided the best overall improved performance for both non disabled and disabled participants. 5.2.4. Physical exertion Participants were asked to rate on the rating of perceived exertion (Borg, 1998) the amount of physical effort that they had to exert to maintain an upright driving posture whilst driving. A Wilcoxon test showed that for all participants the perceived exertion for the circuit task was significantly higher than the hill task when no support aids were present (Z ¼ 2.99, p ¼ 0.003). The disabled drivers reported significantly greater ratings of perceived physical exertion than the non disabled drivers for both the circuit and hill tasks when no support aids were present (Trial sessions A and F). Based on a Friedman’s nonparametric repeated measures test the addition of support aids did affect the perceived level of physical effort (w2 ¼ 21.7, po0.001). The multiple paired comparison technique described by Dancey and Reidy (2002) using an adjusted probability level (achieved significance level, 0.05/4 ¼ 0.0125) showed that only disabled drivers gained a significant reduction in perceived physical exertion from the presence of support aids, and this was only achieved from the combinations of support aids used in Trials
session E (the use of the pelvic support in conjunction with thoracic and the shoulder harness, po0.01). This finding was supported by the subjective ratings given for the level of lateral support each support aid provided. Sixty-eight percent of participants rated sessions E as providing ‘Good’ or ‘Very good’ levels of lateral support. There was no significant difference between all the other different combinations of support aids when compared to no support aid conditions for the amount of reported physical exertion in maintaining an upright driving posture. 5.2.5. User acceptance of support aids Fig. 6 shows the support aids participants reported as being most effective and Fig. 7 shows the support aids participants said they would use again. Just under half of disabled participants (40%) stated that they would not use any of the support aids again although they had previously indicated particular aids as improving their driving performance and confidence. This was attributed to the discomfort caused by the support aids (Table 5), the difficulty in fitting the support aids, and concern over the difficulty of gaining a rapid exit from the vehicle in the event of an emergency. In addition, five participants stated that they did not like the obvious presence of the support aids, in particular, commenting that they felt that the conspicuous appearance of the thoracic support identified/ highlighted them as having a disability and being perceived as different to other drivers. 6. Discussion Results from the telephone questionnaire show that maintaining an upright driving position was a problem for
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9% (n=2) , 0% Pelvic support 9% (n=2)
26% (n=6) Thoracic support
4% (n=1) Shoulder harness Pelvic support combined with Thoracic support
13% (n=3)
Thoracic support combined with Shoulder harness None
39% (n=9)
Fig. 6. Combinations of support aids regarded as most effective by disabled participants.
22% (n=5) Pelvic support Thoracic support
40% (n=9)
Shoulder harness Pelvic support combined with Thoracic support 26% (n=6) 4% (n=1)
None
4% (n=1)
4% (n=1)
Thoracic support combined with Shoulder harness
Fig. 7. Disabled participants’ preference for the supports aids that they would use again.
Table 5 Number of participants reporting discomfort from the support aids and the body area affected Reported body part experiencing pain and/or discomfort
A B No support Pelvic aids 1 support
C Pelvic support and thoracic support
D Pelvic support and shoulder harness
E F Pelvic support, thoracic and No support shoulder harness aids 2
Neck Both shoulders Left shoulder Right shoulder Both arms Both upper arms Under arm pits Rib cage Chest Waist Both legs Upper legs Upper back Lower back Buttocks
0 0 0 0 0 0 0 0 0 0 0 2 0 6 0
0 0 0 0 1 2 2 3 0 1 0 0 0 1 0
1 6 1 2 0 1 7 0 0 0 0 0 5 0 0
1 3 1 2 0 0 6 1 2 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
a high percentage of disabled drivers. Sixty-six percent needed to brace themselves compared to 12% of non disabled drivers. Twenty-four disabled drivers (41%) reported that they found themselves leaning to one side from which they found it difficult to readjust to an upright
0 0 0 0 0 0 0 0 0 0 1 0 0 2 1
driving position. Such extreme changes in posture were not observed from the interior video footage of the driving trials, rather results showed that disabled drivers used physical effort and bracing to maintain an upright driving position during the short driving sessions of the trials. It is
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suggested that on longer journeys fatigue would result and would cause gradual gross changes in driving position. This is supported by results from the telephone questionnaire. Results from the driving trials show that disabled drivers attained equal driving performance (vehicle speed and driving accuracy) as non-disabled drivers but at the expense of greater physical effort. Findings from this study show that in the driving sessions where no support aids were used disabled drivers braced themselves more whilst driving than non disabled drivers. However, when support aids were used the number of bracing points used by disabled drivers was significantly reduced and there was also a significant reduction in participants ratings of perceived physical effort in maintaining an upright driving position. All of the support aids used in the driving trials were found to have a positive effect on driving performance in terms of; driving speed, driving accuracy, My moment on the steering wheel, number of bracing points and driving confidence compared to when no support aids were used. Results showed that two combinations (support aids used in sessions C and E) were particularly beneficial for the disabled drivers and were the overall best performers. In particular, additional lateral support provided to the trunk was of benefit to the disabled drivers. The shoulder harness performed best when worn in addition to the thoracic support (Trial session E); however, when the shoulder harness was worn with just the pelvic support (D) the effects were less positive and not statistically significant. Although participants recognized and reported the improved effects of using the support aids, in terms of their driving performance, 40% stated that they would not use any of the supports aids again or the support aids that they would use again did not correspond with those that they had previously stated as giving them greatest performance benefits. Other factors, such as comfort and ease of fitting, had a significant effect on whether participants would use particular aids again. The shoulder harness and thoracic support were reported by a high number of respondents as being difficult to adjust or to put on and nearly all participants reported experiencing discomfort/pain from the buckles of the shoulder harness.
7. Conclusions Disabled drivers attained equal driving performance as non disabled drivers but at the expense of greater physical effort. The extra effort required from disabled drivers to maintain an upright driving position may have an impact on long journeys. Increased fatigue may have an adverse affect on driving performance in terms of control of the vehicle, duration of driving, driver comfort and attention. It is important that disabled drivers who suffer problems with their driving posture should recognise the increased risk of fatigue. The addition of support aids can reduce the physical demands placed on the disabled driver and improve driving performance. However, these devices need
to be further refined to improve usability and appearance to make them more acceptable to their end users. 7.1. Recommendations and future work The study has shown the benefits available to disabled drivers through the use of postural supports. However, effective use of such products is limited by a number of factors which the recommendations below aim to address. 7.1.1. Support design Although the study demonstrated improved driving performance with the use of supports (which the drivers themselves readily acknowledged), only half said that they would use such supports in the future. Reasons for this were discomfort, difficulty in use and the conspicuous appearance of the supports. Efforts to address these aspects, in a cost-effective manner, would assist in overcoming these current limits to use. 7.1.2. Driver information Improving the design of the supports needs to be complemented by making drivers aware of their potential benefits available to increase motivation to use such products. Research needs to be undertaken to determine the most effective means for this information dissemination. 7.1.3. Usability database There would be value in developing a national database to which users of postural supports could contribute information concerning their disability, the support they use, the benefits they derive, problems they experience, etc. One advantage of such a system would be that the comments could be made based on the experience of long-term use of the products. Such a database could be used by drivers themselves as well as driving assessors in order to determine the supports most likely to be of assistance. 7.1.4. Vehicle design A complementary area for improvement for disabled drivers is to improve the interior design of the vehicle to increase and optimise the areas available to support bracing by the driver. Research would be required to determine the most effective location and design of bracing points so as to support and maintain a good driver posture. 7.2. Limitations of the study It is acknowledged that disabled people are very diverse in their physical ability and anthropometry and this presents difficulties in terms of conducting this type of study and forming firm conclusions that can be applied generally across populations. In an attempt to overcome the problem of diversity the study also conducted a more refined analysis, in which, in addition to making
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comparisons between non disabled and disabled drivers, separate analyses of the data were conducted when participants were grouped by (1) level of mobility and (2) the types of vehicle controls used. Although the numbers of participants in these subgroups were small (4–13) specific differences between the different subgroups in terms of trends in postural support strategies and the most effective support aids were identified. Results from this study provide an indication of which support aids are likely to be of benefit for particular individuals based on the type of controls individuals use within their vehicles. It could be argued that the participants in the driving trials were to some extent self selecting in that only drivers who were able to drive the distance to the test circuit participated. Results from the telephone questionnaire support this, disabled drivers who experienced large changes in posture or discomfort typically limited the distances and duration they would drive. To account for this the telephone questionnaire was conducted to provide a context in which findings from the driving trials could be referred and related back to a larger population and to the real-world driving environment. Acknowledgement We acknowledge our thanks to Accessibility and Equalities Unit, Department for Transport, Great Minster House. 76 Marsham Street, London, SW1P 4DR, UK.
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Applied Ergonomics 39 (2008) 47–55 www.elsevier.com/locate/apergo
Postural support strategies of disabled drivers and the effectiveness of postural support aids Clare Lawtona,, Sharon Cooka, Andrew Maya, Keith Clemob, Susan Brownc a
Ergonomics and Safety Research Institute, Loughborough University, Loughborough LE11 3UZ, UK Motor Industry Research Association (MIRA), Watling Street, Nuneaton, Warwickshire CV10 OUT, UK c Derby Assistive Technology Evaluation Centre, Derby City Hospital, Uttoxeter Road, Derby DE22 3NE, UK b
Received 16 March 2006; accepted 11 March 2007
Abstract The paper discusses a series of driving trials that were conducted to investigate postural stability of disabled drivers and to assess the effectiveness of a representative sample of support aids. Twenty-three disabled drivers with varying levels of physical disability and seven non disabled drivers participated in the study. The test car was equipped with transducers to measure vehicle velocity and acceleration (longitudinal and lateral), steering wheel movement and torque, and the bracing forces exerted by the driver on the steering wheel. Video cameras were installed to record postural support strategies and displacement of the driver and to record deviation of the car from the specified path. Subjective data regarding driver attitudes and acceptance were also collected through the administration of questionnaires. Findings from the study showed that support aids significantly improved driving performance and reduced physical exertion to maintain an upright driving position for disabled drivers. However, ergonomics design aspects regarding the ease of use and acceptance of the support aids by the end users were identified as obstacles to their sustained use in everyday driving. r 2007 Elsevier Ltd. All rights reserved. Keywords: Disabled; Drivers; Posture
1. Introduction Although someone may be well balanced when sitting in a static environment, things change when driving. Driving is a very dynamic task which imposes lateral and longitudinal forces on the driver which will throw most people out of balance. The driver must be able to compensate for these forces and return to a safe, upright position without losing hand placement or inadvertently moving the wrong controls. Drivers often subconsciously brace themselves within the vehicle whilst driving to maintain an upright position or make small adjustments to their posture after a particular manoveuer (Andreoni et al., 2002; Reed et al., 2000; Coelho and Dahlman, 1997). However, for drivers who have a physical disability resulting in impaired balance or reduced upper body strength, or have reduced lower limb function for example, these compensatory actions Corresponding author. Tel.: +44 1509 226900; fax:+44 1509 226960.
E-mail address: [email protected] (C. Lawton). 0003-6870/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.apergo.2007.03.005
may be difficult to achieve. This may affect the operation of controls and have a resultant impact on safety. Haslegrave (1986) states that there is currently insufficient knowledge of the extent and causes of disabled driver accidents and incidents and that further research is required. Twenty years on, data are still very limited. Although incident and accident data are few, research does indicate that driving a car adapted for a disabled person is far more laborious and fatiguing for a person with a physical disability. Disabled drivers often experience additional physical demands, i.e. forces required to activate adapted controls such as conversion of the accelerator and brake from foot to hand operation, conversion from hand steering to foot steering, and relocation of the minor controls (Peters, 2001; Haslegrave, 1989). Reducing the energy required to maintain an upright driving position is important for disabled drivers as this will help maximise driving comfort, duration and safety. To gain a stable driving position disabled drivers are first encouraged to use their original car seat. However, standard car seats having
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sufficient adjustment options tend to be available only in the top of the range models. Consequently, products have been developed that can be added to any standard car seat to provide improved support (postural support aids). 2. Study aims The aims of the study were to investigate whether postural stability is an issue of concern for disabled drivers and to assess the effectiveness of support aids that are currently available.
journey resulting in awkward and inefficient postures. Awkward postures when sustained for prolonged periods of time will increase muscular loads and increase the likelihood of fatigue and perceived levels of discomfort (Park et al., 2002; Silverstein, 1995). Fatigue is a particularly important consideration for disabled drivers with spinal cord injury as the risk of spastic cramps increases with increasing load and tiredness. 4. Method 4.1. Overview
3. The driving environment for disabled drivers 3.1. Seating Many disabled people will sit on a cushion to improve their comfort while driving, because they are short in stature and/or to prevent pressure sores (Murray-Leslie, 1990). However, the addition of seat cushions may increase driver instability (Coopers, 1986). The use of smooth seating surfaces that are aimed at easing ingress and egress to the vehicle may also further reduce postural stability, increasing the likelihood of gross changes in posture. 3.2. Number of contact/bracing points In addition to the seat itself, the seat in combination with the steering wheel and vehicle body components (window edges, etc.) can act to provide a supportive framework. However, certain vehicle control adaptations can reduce the number of contact points available, for example when the driver must steer with one hand whilst using a hand accelerator/brake control arrangement. Points of contact may also be lost for amputees and where a driver has suffered loss of sensation in part of the body. The loss of those bracing points may increase the physical demands placed on other body parts as they act to compensate. 3.3. Making the vehicle fit the driver The layout of controls may not be ideal for all drivers with a disability due to the great variation in anthropometric dimensions of disabled drivers. To compensate for potential limitations/misfit of control adaptations disabled drivers often adjust seating features to gain functionality rather than support and comfort (Cornwell, 1985). 3.4. Physical effort and fatigue Disabled drivers may already be exposed to high physical demands in terms of strength and effort, resulting from either the adaptation to their car controls or simply overcoming the physical constraints of their disability (Peters, 2001). In addition, initial instability may lead to progressive deterioration of driving position during the
The study consists of two parts: a set of exploratory structured telephone interviews and a series of driving trials. The driving trials were conducted to verify findings from the interviews and to assess, in more detail, postural support strategies engaged whilst driving and the effectiveness of a range of support aids in terms of improving driver comfort, physical effort and driving performance. 4.2. Participants 4.2.1. Structured interviews Telephone questionnaires were conducted with 58 disabled drivers and 17 non-disabled drivers. A larger sample of disabled participants was actively sort to account for greater variation in anthropometric dimensions and physical capabilities of the disabled driver population. Table 1 shows the medical conditions of disabled respondents. 4.2.2. Driving trials Driving trials were conducted with 23 disabled and 7 non-disabled participants. Again to account for greater variation in the disabled driver population a larger sample than non-disabled drivers participated in the study to provide a more representative sample. Participants for the driving trials were randomly selected from respondents to the telephone interviews that had stated an interest in participating further in the study. Participants were required to be 17 years and above, hold a current driving
Table 1 Medical conditions of respondents to the questionnaire Medical condition and the number of respondents Arachoditis (n ¼ 1), arthritis (n ¼ 6), artificial limb (n ¼ 1), broken back (n ¼ 1), broken coccyx and fibromyaligia (n ¼ 1), cerebral palsy (n ¼ 2), cerebral palsy and quadriplegia (n ¼ 1), congenital lower limb deformity (n ¼ 1), degrading spine (n ¼ 3), faulty knee replacement (n ¼ 1), fused spine (n ¼ 1), MS (n ¼ 6), muscular dystrophy (n ¼ 1), nerve disease and spinal injury (n ¼ 1), Not specified (n ¼ 2), paralysis of left leg (n ¼ 1), paraplegia (n ¼ 5), paraplegia and MS (n ¼ 1), polio (n ¼ 5), short arms (n ¼ 1), spastic diaplegic-paralysis (n ¼ 1), spondylitis (n ¼ 1), stroke (n ¼ 5), TB and hip double replacement (n ¼ 1), tendons cut in left knee (n ¼ 1), tetraplegia (n ¼ 6), tumour in spine (n ¼ 1), weak legs (n ¼ 1).
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licence and where appropriate have a physical impairment or disability. The aim was to include participants with a range of disabilities including stroke and high spinal lesions. The participants’ ages ranged from 23 to 84 years, with a mean age of 53 years. Of the disabled driver participants, 20 people used a wheelchair. All participants who used a wheelchair transferred into vehicles and drove from a standard car seat. The numbers of participants within each medical diagnosis group were low, as shown in Table 2. Results from the telephone questionnaire indicated the need to conduct an analysis based on physical ability reflected in the type of controls/adaptations used in the vehicle rather than medical condition per se. Therefore, for analysis purposes participants were grouped based on the types of vehicle controls/adaptations used. Although not a set standard, this method enabled a consistent means of categorising participants into workable subgroups. The aim of this base level of categorisation was to enable identification of patterns between these broad subgroups and the data collected during the trials. Due to small numbers in some of the categories, analysis was limited to the three larger groups consisting of more than four participants; these are italicized in Table 3. 4.3. Methods 4.3.1. Structured interviews The telephone interviews probed issues relating to postural stability, these included information regarding driving tasks/manoeuvres, type of vehicle driven, type of
Table 2 Medical conditions of disabled drivers participating in the driving trials Medical condition and number of participants
vehicle controls, duration of journey times, use of additional support, whether discomfort was experienced, whether postural changes occurred. The interview was also used to recruit people to participate in the driving trials. 4.3.2. Driving trials A 2000 model year Renault Megane Scenic Automatic was used. For drivers using adapted controls, suitable adaptations were fitted (Table 3). The test vehicle was fitted with Setra 2g and Endevco 2g accelerometers to measure lateral and longitudinal accelerations, respectively. Vehicle speed was measured using a Datron microwave speed sensor. Any disturbance of the driver’s position resulting from vehicle acceleration was recorded using two video cameras that were fitted inside the vehicle to record images from two different perspectives (side-on and overhead view) of the driver. The extent of deviation from the upright position could then be observed and matched to particular driving tasks. In order to assess the amount of bracing during the manoeuvres, the forces and moments exerted by the driver on the steering wheel were measured. A steering wheel with four spokes was fitted (Fig. 1). Each spoke was fitted with strain gauges to measure the force parallel to the steering column axis. An additional transducer (a steering wheel force load cell (FTSS Child dummy neck transducer)) and a MIRA steering potentiometer was fitted between the steering wheel and column to measure steering wheel movement/angle (control input) and steering torque. All data were filtered and amplified by an ASTECH 16 PIX, Programmable Signal Conditioning Unit and subsequently digitised and recorded using a DAQBOOK Series 200 Analog to Digital Converter. Digitised signals were analysed using Diadem software on a standard PC. Two techniques for assessing a driver’s lateral (steering) control were devised. The first technique used the standard
Archoditis and nerve disease and spinal (n ¼ 1), arthritis (n ¼ 2), cerebral palsy (n ¼ 1), cerebral palsy and quadriplegia (n ¼ 1), congenital lower limb deformity (n ¼ 1), faulty knee replacement (n ¼ 1), fused spine (n ¼ 1), MS (n ¼ 2), muscular dystrophy (n ¼ 1), paraplegia (n ¼ 2), polio (n ¼ 3), short arms (n ¼ 1), spastic diaplegia-paralysis from L1 (n ¼ 1), stroke (n ¼ 1), TB and double hip replacement (n ¼ 1), tetraplegia (n ¼ 3).
Table 3 The number of disabled participants and type of vehicle controls Steering controls
Brake/ accelerator controls
Standard foot controls
Adapted to hand controls
Standard steering wheel
Spinner attached to the steering wheel
12 (7 nondisabled and 5 disabled participants) 1
4
49
13 Fig. 1. Interior view of the test vehicle.
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deviation of steering angle when the car was negotiating the turns. The second technique consisted of asking the driver to steer so as to maintain as accurately as possible the outside edge of the front right-hand tyre with the left-hand edge of a white line painted on the road surface. The car was fitted with a transverse scale extending from the right front corner of the car. A video camera mounted above this and looking downwards continuously filmed the intersection of the white line on the scale (Fig. 2). This was later analysed to measure the deviation of the car from its intended path. The measurements of braking accuracy were also taken using the same video camera and scale. In addition to the objective performance data described above, subjective data relating to the drivers’ reported accounts of their experiences and impressions of driving with the supports and any bracing strategies were recorded using a series of rating scales and open-ended questions. 4.3.3. Procedure The driving trials consisted of: driving round a figure of eight circuit (to investigate the effects of lateral acceleration), ascending and descending a steep hill and braking on the descent (to investigate the effects of longitudinal acceleration and deceleration). The first and last driving sessions were conducted in the standard car seat, without
the addition of any support aids. All other sessions were conducted with the addition of progressive levels of postural support (referred to as Trials A–F, Table 4). Each trial required the completion of three consecutive circuits of the figure of eight course which was marked out by a white line on the tarmac and three consecutive ascents and descents of the hill. For the first two circuits, a target speed was suggested of 16 km/h (10 mph), then 24 km/h (15 mph) whilst for the third circuit the subject was invited to drive at the maximum speed they felt they could confidently maintain. 4.3.4. Performance measures The mean speeds attained by each participant when cornering the left and right bends in the third circuit of the figure of eight tasks were used as a performance indicator (the third circuit had no set speed and was determined by the participant). The standard deviation of steering angle during each cornering was also calculated to provide a measure of driving accuracy. After each driving session, a series of rating scales were used to capture data of ratings of perceived exertion (Borg, 1998), driver confidence, perceived ease of use, comfort and bracing points. 4.4. Selection of support aids A comprehensive market review of support aids was undertaken. Support aids were grouped by generic characteristics and were split into three categories, aids that provided: lateral support to the pelvis, lateral support to the trunk and longitudinal support to the trunk. A representative support aid was selected from each category to be used in the trials. Selected support aids included: a pelvic support belt that was designed to provide lateral support to the pelvis, a Thoracic support that provided lateral support to the trunk, and a shoulder harness that was designed to provide longitudinal support to the trunk (Fig. 3). The effectiveness of these aids was assessed in the driving trials when they were used in isolation and in combination with one another.
Fig. 2. Aerial view of transverse scale extending from the right front corner of the test vehicle.
Table 4 Support aids used in Trail sessions A to F Pelvis support A B C D E F
No support aids | | | | No support aids
Thoracic support
Shoulder harness
| |
| | Fig. 3. Selected postural support aids.
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5. Results 5.1. Telephone questionnaire—reported postural difficulties Fifty-eight disabled drivers and 17 non-disabled drivers were interviewed. Results from the telephone interviews found that postural stability is an issue for a high percentage of disabled drivers that responded. Thirty-eight of disabled drivers interviewed (66%) reported the need to stabilise or brace themselves against something whilst driving. Furthermore, although bracing occurred for a high percentage of disabled drivers they still reported that large postural changes occurred from which they could not then right themselves into an upright driving position. The predominant postural change reported was the propensity to end up leaning to one side reported by 24 disabled drivers (41%). In comparison, only two of the non-disabled drivers reported changes in posture and both stated they were able to easily right themselves. None of the nondisabled drivers reported any problems in maintaining an upright driving position while driving. 5.2. Driving trials
Percentage of participant group
5.2.1. Postural support behaviours when no support aids present There was a significant difference in the number of bracing points used by non-disabled and disabled drivers (U ¼ 37, p ¼ 0.035). Results from the driving trials found that when no support aids were present, six out of seven (86%) of non disabled drivers reported using 0 or 1 location for bracing, whereas disabled drivers reported using 1–4 different bracing locations. Disabled participants that drove using hand controls for acceleration and braking and steered using a spinner (enabling one handed steering) reported using a higher number of different
bracing points than other disabled drivers, with 7 out of the 13 (54%) reporting using two or more different bracing points (Fig. 4). Areas within the vehicle that participants braced concurred with observations made from the video footage and varied depending on the type of controls people used. The seat back and the central consol were used for bracing by three out of the four drivers (75%) using ‘steering with spinner and standard foot controls’ (disabled participants with restricted upper limb function). Whereas the majority of participants that used a spinner in combination with hand controls (slightly restricted upper limb and greatly restricted lower limbs) (8 out of 13, 61.5%) relied on the arm rest in the door for bracing. 5.2.2. Postural support behaviours when support aids present For all participants (non-disabled and disabled drivers) the need to brace decreased as more support aids were used. For disabled drivers, the combined use of the pelvic support and shoulder harness (Trials session D, Fig. 5) reduced the need for bracing for a large percentage of disabled participants (65%), with only 8 out of 23 (35%) bracing themselves against something within the vehicle when wearing these aids, compared to 20 out of 23 (85%) when no support aids were present (A and F). For nondisabled drivers, the pelvic support and thoracic support (Trial session C) reduced the need for bracing for six out of seven (85%), with only one out of 7 (14%) of this group needing to brace themselves when wearing these aids compared to 5 out of seven (71%) when no support aids were used. 5.2.3. Driving performance There were no significant differences between driving performance of the disabled and non disabled participants in terms of speed and driving accuracy in the trial sessions when no support aids were present (A and F). All of the
100% 90%
8% (n=1)
14% (n=1)
25% (n=1)
15% (n=2)
25% (n=1)3
1% (n=4)
40% (n=2)
80% 70% 60%
2 bracing points
40% 60% (n=3)
30% 10%
4 bracing points 3 bracing points
57% (n=4)
50%
20%
51
23% (n=3)
1 bracing point
50% (n=2)
29% (n=2)
23% (n=3)
0 bracing points
0% Standard steering Standard steering wheel and wheel and standard foot standard foot control (non control (disabled) disabled)
Steering with spinner and standard foot controls
Steering with spinnerand hand controls
Participants groups based on vehicle controls Fig. 4. Percentage of each respondent group (based on type of vehicle controls) and the number of bracing points used in Trial session A (no support aids present).
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100 Percentage of participants
90 80
n=20
Non disabled participants
n=19 n=5
70
Disabled participants
n=14
n=4
60 50
n=3
n=3
40
n=20
n=8
n=3 n=9
30 20
n=1
10 0 No support aids 1
A
Pelvic support Pelvic support Pelvic support Pelvic and Thoracic and Shoulder support, support harness Thoracicand Shoulder harness B
C
D
E
No support aids 2
F
Trial session (support aids used) Fig. 5. Percentage of participants that reported bracing themselves during the trial sessions.
support aids were found to have a positive affect on driving performance for both the non-disabled and disabled drivers. Speed, driving accuracy, My moment (the moments about the vertical axis of the steering wheel), number of bracing points, and driver confidence were all significantly improved when compared to the no support aids present trial sessions (A and F). Support aid combinations used in Trial sessions C (pelvic and thoracic support) and E (pelvic, thoracic support and shoulder harness) provided the best overall improved performance for both non disabled and disabled participants. 5.2.4. Physical exertion Participants were asked to rate on the rating of perceived exertion (Borg, 1998) the amount of physical effort that they had to exert to maintain an upright driving posture whilst driving. A Wilcoxon test showed that for all participants the perceived exertion for the circuit task was significantly higher than the hill task when no support aids were present (Z ¼ 2.99, p ¼ 0.003). The disabled drivers reported significantly greater ratings of perceived physical exertion than the non disabled drivers for both the circuit and hill tasks when no support aids were present (Trial sessions A and F). Based on a Friedman’s nonparametric repeated measures test the addition of support aids did affect the perceived level of physical effort (w2 ¼ 21.7, po0.001). The multiple paired comparison technique described by Dancey and Reidy (2002) using an adjusted probability level (achieved significance level, 0.05/4 ¼ 0.0125) showed that only disabled drivers gained a significant reduction in perceived physical exertion from the presence of support aids, and this was only achieved from the combinations of support aids used in Trials
session E (the use of the pelvic support in conjunction with thoracic and the shoulder harness, po0.01). This finding was supported by the subjective ratings given for the level of lateral support each support aid provided. Sixty-eight percent of participants rated sessions E as providing ‘Good’ or ‘Very good’ levels of lateral support. There was no significant difference between all the other different combinations of support aids when compared to no support aid conditions for the amount of reported physical exertion in maintaining an upright driving posture. 5.2.5. User acceptance of support aids Fig. 6 shows the support aids participants reported as being most effective and Fig. 7 shows the support aids participants said they would use again. Just under half of disabled participants (40%) stated that they would not use any of the support aids again although they had previously indicated particular aids as improving their driving performance and confidence. This was attributed to the discomfort caused by the support aids (Table 5), the difficulty in fitting the support aids, and concern over the difficulty of gaining a rapid exit from the vehicle in the event of an emergency. In addition, five participants stated that they did not like the obvious presence of the support aids, in particular, commenting that they felt that the conspicuous appearance of the thoracic support identified/ highlighted them as having a disability and being perceived as different to other drivers. 6. Discussion Results from the telephone questionnaire show that maintaining an upright driving position was a problem for
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9% (n=2) , 0% Pelvic support 9% (n=2)
26% (n=6) Thoracic support
4% (n=1) Shoulder harness Pelvic support combined with Thoracic support
13% (n=3)
Thoracic support combined with Shoulder harness None
39% (n=9)
Fig. 6. Combinations of support aids regarded as most effective by disabled participants.
22% (n=5) Pelvic support Thoracic support
40% (n=9)
Shoulder harness Pelvic support combined with Thoracic support 26% (n=6) 4% (n=1)
None
4% (n=1)
4% (n=1)
Thoracic support combined with Shoulder harness
Fig. 7. Disabled participants’ preference for the supports aids that they would use again.
Table 5 Number of participants reporting discomfort from the support aids and the body area affected Reported body part experiencing pain and/or discomfort
A B No support Pelvic aids 1 support
C Pelvic support and thoracic support
D Pelvic support and shoulder harness
E F Pelvic support, thoracic and No support shoulder harness aids 2
Neck Both shoulders Left shoulder Right shoulder Both arms Both upper arms Under arm pits Rib cage Chest Waist Both legs Upper legs Upper back Lower back Buttocks
0 0 0 0 0 0 0 0 0 0 0 2 0 6 0
0 0 0 0 1 2 2 3 0 1 0 0 0 1 0
1 6 1 2 0 1 7 0 0 0 0 0 5 0 0
1 3 1 2 0 0 6 1 2 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
a high percentage of disabled drivers. Sixty-six percent needed to brace themselves compared to 12% of non disabled drivers. Twenty-four disabled drivers (41%) reported that they found themselves leaning to one side from which they found it difficult to readjust to an upright
0 0 0 0 0 0 0 0 0 0 1 0 0 2 1
driving position. Such extreme changes in posture were not observed from the interior video footage of the driving trials, rather results showed that disabled drivers used physical effort and bracing to maintain an upright driving position during the short driving sessions of the trials. It is
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suggested that on longer journeys fatigue would result and would cause gradual gross changes in driving position. This is supported by results from the telephone questionnaire. Results from the driving trials show that disabled drivers attained equal driving performance (vehicle speed and driving accuracy) as non-disabled drivers but at the expense of greater physical effort. Findings from this study show that in the driving sessions where no support aids were used disabled drivers braced themselves more whilst driving than non disabled drivers. However, when support aids were used the number of bracing points used by disabled drivers was significantly reduced and there was also a significant reduction in participants ratings of perceived physical effort in maintaining an upright driving position. All of the support aids used in the driving trials were found to have a positive effect on driving performance in terms of; driving speed, driving accuracy, My moment on the steering wheel, number of bracing points and driving confidence compared to when no support aids were used. Results showed that two combinations (support aids used in sessions C and E) were particularly beneficial for the disabled drivers and were the overall best performers. In particular, additional lateral support provided to the trunk was of benefit to the disabled drivers. The shoulder harness performed best when worn in addition to the thoracic support (Trial session E); however, when the shoulder harness was worn with just the pelvic support (D) the effects were less positive and not statistically significant. Although participants recognized and reported the improved effects of using the support aids, in terms of their driving performance, 40% stated that they would not use any of the supports aids again or the support aids that they would use again did not correspond with those that they had previously stated as giving them greatest performance benefits. Other factors, such as comfort and ease of fitting, had a significant effect on whether participants would use particular aids again. The shoulder harness and thoracic support were reported by a high number of respondents as being difficult to adjust or to put on and nearly all participants reported experiencing discomfort/pain from the buckles of the shoulder harness.
7. Conclusions Disabled drivers attained equal driving performance as non disabled drivers but at the expense of greater physical effort. The extra effort required from disabled drivers to maintain an upright driving position may have an impact on long journeys. Increased fatigue may have an adverse affect on driving performance in terms of control of the vehicle, duration of driving, driver comfort and attention. It is important that disabled drivers who suffer problems with their driving posture should recognise the increased risk of fatigue. The addition of support aids can reduce the physical demands placed on the disabled driver and improve driving performance. However, these devices need
to be further refined to improve usability and appearance to make them more acceptable to their end users. 7.1. Recommendations and future work The study has shown the benefits available to disabled drivers through the use of postural supports. However, effective use of such products is limited by a number of factors which the recommendations below aim to address. 7.1.1. Support design Although the study demonstrated improved driving performance with the use of supports (which the drivers themselves readily acknowledged), only half said that they would use such supports in the future. Reasons for this were discomfort, difficulty in use and the conspicuous appearance of the supports. Efforts to address these aspects, in a cost-effective manner, would assist in overcoming these current limits to use. 7.1.2. Driver information Improving the design of the supports needs to be complemented by making drivers aware of their potential benefits available to increase motivation to use such products. Research needs to be undertaken to determine the most effective means for this information dissemination. 7.1.3. Usability database There would be value in developing a national database to which users of postural supports could contribute information concerning their disability, the support they use, the benefits they derive, problems they experience, etc. One advantage of such a system would be that the comments could be made based on the experience of long-term use of the products. Such a database could be used by drivers themselves as well as driving assessors in order to determine the supports most likely to be of assistance. 7.1.4. Vehicle design A complementary area for improvement for disabled drivers is to improve the interior design of the vehicle to increase and optimise the areas available to support bracing by the driver. Research would be required to determine the most effective location and design of bracing points so as to support and maintain a good driver posture. 7.2. Limitations of the study It is acknowledged that disabled people are very diverse in their physical ability and anthropometry and this presents difficulties in terms of conducting this type of study and forming firm conclusions that can be applied generally across populations. In an attempt to overcome the problem of diversity the study also conducted a more refined analysis, in which, in addition to making
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comparisons between non disabled and disabled drivers, separate analyses of the data were conducted when participants were grouped by (1) level of mobility and (2) the types of vehicle controls used. Although the numbers of participants in these subgroups were small (4–13) specific differences between the different subgroups in terms of trends in postural support strategies and the most effective support aids were identified. Results from this study provide an indication of which support aids are likely to be of benefit for particular individuals based on the type of controls individuals use within their vehicles. It could be argued that the participants in the driving trials were to some extent self selecting in that only drivers who were able to drive the distance to the test circuit participated. Results from the telephone questionnaire support this, disabled drivers who experienced large changes in posture or discomfort typically limited the distances and duration they would drive. To account for this the telephone questionnaire was conducted to provide a context in which findings from the driving trials could be referred and related back to a larger population and to the real-world driving environment. Acknowledgement We acknowledge our thanks to Accessibility and Equalities Unit, Department for Transport, Great Minster House. 76 Marsham Street, London, SW1P 4DR, UK.
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