Functional task-oriented anthropometric measurements. (Taken from Roe (1993) p. 14, reprinted with permission)
The purpose of this chapter is to explore the process and general issues that OTs need to consider when assessing an individual’s capacities and impairments and matching these to the available driver-cabin environment.
Candidates for the Intervention
The task of driving may be performed for a range of purposes including general community mobility , paid or voluntary work, to access leisure facilities, goods and services, and to fulfill family, social, or vocational roles (Coughlin 2001). OTs may address vehicle driver-cabin configuration issues with any client of driving age with body function impairments or disabilities. Eligibility for driver-related services include (1) the client has the potential to be an independent driver, (2) they meet licensing requirements for that jurisdiction, and (3) they comply with compulsory national medical standards (e.g., Austroads 2012; Canadian Medical Association 2006; Johnson 2013). Other considerations such as access to a vehicle and financial resources to pay for OT services, vehicle modifications and specialist driving lessons, may also influence client assessment and interventions .
Frequency of Use
Driving a private motor vehicle is a common transportation choice associated with personal independence and quality of life , particularly for older people (ABS 2005; Byszewski et al. 2010). There is also evidence of a large and increasing demand for vocationally related vehicle use, as private vehicles are driven for work purposes, including incidental travel between workplaces and use as a mobile office within which to execute a variety of work tasks (Stuckey et al. 2007).
Consideration of vehicle driver-cabin configurations are included as part of the community and vocational mobility component of an occupational therapy rehabilitation intervention as well as driver rehabilitation evaluation services conducted by OTDAs .
The Role of the OT
Generalist OTs are able to consider many vehicle driver-cabin mismatches that may impact on drivers with physical and sensory disabilities. Their role is to identify simple driver or vehicle adaptations that may improve independence. Generalist OTs must identify the need for referral to OTDAs. Specialist OTDAs, who have particular expertise in driver evaluation and rehabilitation, consider in more detail the broader range of requirements that impact the task of driving . OTDAs conduct off-road and on-road evaluations which are used to identify driver needs within the real-world task environment. OTDAs may also liaise with vehicle modifiers and driving instructors as well as report to the jurisdictional driver licensing authority to address driver licensing and vehicle registration requirements (Di Stefano and Macdonald 2010; Stav 2004).
An Assessment Framework: Ergonomics
It is useful to conceptualize the factors which interact to determine the fit between a particular client, access/egress requirements, driving controls and displays, and other vehicle-cabin features required to optimize driver placement, comfort, and safety. A simple generic depiction of the ergonomic issues that impact on driver vehicle-cabin configurations is presented in Fig. 17.2. This shows that there are four main components: centrally (A), the driver who functions within the vehicle cabin (B), the external environment including the physical real-world immediate context (C) and the legislative, regulatory, and policy systems which impact upon licensing as well as vehicle and road system design (D). The ergonomic framework can help the OT to identify the critical aspects of vehicle driver-cabin configurations and the real-world and broader systems issues that need to be considered. For example, vehicle safety standards and registering requirements (considered within “D” in Fig. 17.2) must be considered if the modification of the driver seat or dashboard controls might interfere with safety features like steering wheel or side air bags (referred to within “B” in Fig. 17.2).
A generic depiction of the ergonomic or systems issues that influence driver vehicle-cabin configurations or interactions
Assessment Issues: Evaluating the Fit Between Driver Characteristics and the Vehicle Cabin
There are general principles which govern good driver seating position in vehicles. These principles apply to all drivers regardless of their anthropometry (body shape and size). Table 17.1 provides seating considerations related to vehicle-cabin design for drivers and includes issues for drivers with impairments considering the ergonomic framework. Items presented are examples only and the list is not exhaustive.
General principles for driver seating and issues relevant to drivers with disabilities
General functional principle
Some examples/OT considerations
1. Seated position
Driver is comfortable with visual access and can reach all primary controls
Encourage use of backrest and head restraint
Positioning the driver correctly in the driver’s seat will optimize postural control in order to see/reach essential vehicle components
Individual anthropometric requirements are met
Optimal seating is required for safety restraint systems to work (e.g., seat belts and air bags)
Individual limb/joint comfort and positioning to optimize function
Seating set-up may need regular reconfiguration, e.g., if vehicle is shared with drivers of different body size and shape
Hip and ankle angles and position for optimal foot pedal operation
Individuals with special needs may need a customized approach to vehicle seating and cabin adjustment
2. Seat posture—adjustment
Hip and ankle angles are important to determine comfortable seating
Hip reference point (HRP) and ankle reference point (ARP) used as key anthropometric baseline “markers”
Ensure hip position in relation to seat pan and backrest angle is appropriate before adjusting other postural elements, e.g., check that driver is sitting with their pelvis well back in the seat with spine supported by the backrest
Lower limb position/placement determines upper limb postural support and comfort
This encourages use of backrest and head restraint
Adjust the lumbar feature (if available) to provide support
3.a. Seat—height for legs
b. Seat—distance to pedals
Seat height should accommodate length of knee/ankle segment and floor/pedal reach
Seat height adjustment should consider hip, knee, and ankle joint comfort, and optimal use ranges
Check there is no pressure from front of seat at the back of the driver’s calves when feet are on cabin floor.
The “ball of foot” should be able to be placed on pedal (not just tip of foot) to ensure energy efficient movement
Move the seat forward to ensure feet can reach pedals and the ankle angles are at no more than about 90 degrees when feet are resting on the cabin floor
Driver’s foot should be able to completely depress the brake pedal and move between pedals comfortably
The closer the driver is to the dashboard, the smaller the angle between the foot and knee joint: this may lead to discomfort and inefficient use of the foot pedals for some people; heels need to be comfortably supported and positioned on the floor
Pedal surfaces should offer some friction to stop foot from slipping
Check foot/ankle position which can influence leg and torso posture and stability required for both static and dynamic postural control: a flat fixed cushion may be sufficient adjustment to raise hip height and therefore reduce hip/knee angles
For pedal operation, with heel on cabin floor, ankle active range of motion should be neutral to permit sufficient plantar flexion as required for pedal depression: if too much dorsiflexion is required when there is no pressure on the pedal, endurance can be reduced
Ensure shoes have soles which permit kinesthetic feedback from pedals
“Bucketing” or notably molded seat pan design may not conform to body shape limiting seated posture depending on driver anthropometry
Seats with combination of vertical and horizontal adjustments are helpful.
4. Seat—height for vision
Driver visual access needs to be sufficient to enable clear view outside of vehicle (front, sides, rear), as well as visual access to all controls
Additional cushions may help but check that seat belt use or positive are not compromised
Driver’s neck needs to be in neutral (no flexion or extension), with eyes forward, comfort sight lines are up to 30 degrees below the horizontal, and should allow easy visual access to dashboard controls and displays
Check that driver can comfortably see out of the front windscreen without tilting head (extending neck)
Ensure visual access to speedometer and other primary displays are not impeded by the steering wheel: consider adjusting steering wheel position
Driver should be able to see over dashboard comfortably and have clear sight lines to internal and external mirrors and when completing head check
5. Seat—distance and reach for primary controls
Ensure comfortable reaches to all primary controls
Access to steering wheel should not be too close (air bag compromised) or too far—avoid too much elbow abduction
Individual anthropometric considerations as well as activity restrictions
Drivers must be able to reach grasp/manipulate the key/ignition system, steering wheel, foot pedals, indicators, hand brake, window wipers, and light controls while remaining in a comfortable seated posture without leaning forward
Access to controls should enable appropriate manipulation
Dashboard should be no further than at wrist level distance when the arm is outstretched
Ensure there is adequate room between the driver’s chest and the front air bag and steering wheel—e.g., > 10–12 in. (25–30 cm)
Consider individual tolerances (endurance and fatigue) when limbs need to be elevated without support
Seat belt lap/sash should sit snugly across pelvis, under the abdomen (not on top of thighs) and shoulder strap diagonally across the sternum
People with special needs may require vehicle modifications
If vehicle controls require adaption—ensure compliance with all regulatory imperatives such as vehicle design rules and registration requirements—refer to OTDA
Driving has been identified as a participation “enabler” and an important aspect of maintaining community engagement, particularly for people with disabilities or those living in rural or regional areas unable to access alternative transport services (Di Stefano et al. 2012; Norweg et al. 2011). As driving cessation may be associated with negative impacts on health and psychosocial status including depression and social isolation, it is important that, whenever possible, individuals can be supported to maintain driving independence (Marotolli et al. 1997, 2000). Personal driving independence, however, must be balanced with the risks associated with undertaking the activity and the potential impact on road safety of errors impacting the driver, passengers, and other road users.
The World Health Organisation (WHO) has recognized the importance of taking a systems approach when addressing road safety globally, highlighting the importance of addressing five key system components: road users, roads, vehicles, post-crash responses, and road safety management (WHO 2010). OTs are well placed to assist with improving the status of road users who are drivers—particularly those with disabilities.
OT decisions around driver/vehicle matches require assessment of driver impairment and capacity, task demands, and the risks related to mismatches (Bridger 2009; Turner-Stokes et al. 1996). Ergonomics aims to minimize the risk to humans by appropriate modification of the human–task–environment fit. Implementation of risk management is most effective when the “hierarchy” of risk controls is employed. This hierarchical approach is based on the evidence that the implementation of interventions which involve physical changes or engineering controls to the tools, task, or environment are more sustainable and effective than those involving driver instruction or behavior change (Quinlan 2010; Safework Australia 2011). The evolution of vehicle safety has seen an increased use of engineering-based design improvements (air bags, automatic brake systems, etc.) as well as those which are designed to reinforce safety behaviors (audible reminders for seat belts, indicators, etc.).
Regardless of the nature of the assessed risk and related hazard or exposures, it is imperative that interventions involving modifications or adaptations comply with applicable regulatory imperatives such as design rules, occupational health and safety directives or local or international standards, or other mandatory requirements (for example, ISO 2009, 2010, 2012). The evidence base for driver/cabin in-vehicle design generally relies on the application of ergonomics principles such as universal design or anthropometric measurements which aim to accommodate 95 % of the population (see for example, Bridger 2009; Salvendy 2012). The interactions between users and the vehicle furniture, displays, controls, and other equipment relevant to the driving task, have long been well documented in ergonomics literature in terms of both physical and cognitive–perceptual characteristics, and form the starting point for expectations of population-based vehicle-user fit (Pheasant 1997; Kroemer 2009).