Clinical Considerations in Driving

In the United States, approximately 11,000 individuals experience a new spinal cord injury (SCI) per year and have varying numbers of disabilities from stroke, muscular dystrophy, ataxia, spina bifida, amputations, reduced upper extremities (traumatic and congenital absence), amyotropic lateral sclerosis (ALS), multiple sclerosis, spinal muscular atrophy, polio, arthrogryposis, osteogenesis imperfecta, rheumatoid arthritis, and various other illnesses.

Each injury, ailment, disease, or disorder has a unique set of motor, sensory, and cognitive issues to be addressed for the person to be considered a safe and independent driver. Each condition may have some expected limitation, but the degree of disability generally varies among individuals. For example, the difference in physical ability of a person who has an SCI can vary significantly depending on the level and complexity of the injury. Further complications can arise if the event that caused the SCI created a secondary effect through a traumatic brain injury (TBI). This impairment may not be noticed until the interactive cognitive skills of driving are required.

The question that must be answered for any potential driver (teen/adult/mature) during a clinical evaluation is whether the driver processes pertinent, environmental traffic information in a timely manner, and executes appropriate and timely responses based on the perceptions of situations encountered. The best person to answer this question is a trained and Certified Driver Rehabilitation Specialist (CDRS). A CDRS is knowledgeable in the selection, use, and application of devices and methods to aid drivers who have disabilities. An unbiased perspective about what type of equipment will work best for a driver can have a huge impact on driver safety, the longevity of their driving career, the cost of the modifications, and the ability to maintain the equipment.

The paths to obtain a referral to a driving evaluation can vary. If the potential driver is a private payer, the vehicle modifier would recommend a local driver evaluation program. If a third-party payer is involved, the CDRS would recommend a driver evaluation program; if the third party is a government entity, the CDRS may have an evaluation program or a contract within one. Various government agencies, such as Veterans Administration, State offices of Vocational Rehabilitation, Workers Compensation Fund, Victims of Crime, Department of Aging, and other health-related departments, may help provide funding for the driver evaluation.

Often a team approach is used to best understand all the details involved in determining the appropriate equipment and training for a safe and independent driver. An occupational therapist will establish the physical and cognitive baseline of a potential driver and a driving instructor will safely guide the driver through basic vehicle functions and an on-the-road evaluation. A rehabilitation engineer will provide equipment and methods for the driver to compensate for any physical limitations. All team members may participate in each portion of the evaluation and in the selection of appropriate assistive driving devices, and in some cases these roles are performed by the same individual.

Most clinicians involved with driving assessments, equipment selection, and driver evaluations are members of the Association for Driver Rehabilitation Specialists (ADED). In 2008, the ADED had approximately 576 members, of which 229 were CDRSs. This number is small compared with the increased need for services to enable older individuals and those who have disabilities to drive. As part of the Quality of Life Technology Engineering Research Center Safe Driving Project, the University of South Florida and University of Pittsburgh are currently evaluating the use of a driving simulator to train individuals who have disabilities to use adaptive driving equipment in a simulated driving environment. Driving simulators have potential to assist in driving assessments because of their relatively low cost, ability to track driver learning, and ability to make instrumentation adjustments on the fly. Obviously, actual road driving remains a key component in the assessment process and when learning safe driving in the community.

Functional Abilities

A battery of tests and assessments are administered to create a baseline from which the CDRS team can appraise safe driving potential. These tests do not necessarily conclude the client’s driving potential; they establish which functional abilities the person has and the limitations that could pose a problem when driving. The client’s ability to compensate for any deficit while behind the wheel is the true test of a driver’s potential. The standardized and nonstandardized tests and assessments to determine safe driving potential address the following factors :

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  Vision and perception: The client is administered standardized test to determine visual acuity and visual fields, color vision, depth perception, contrast sensitivity, processing time, visual tracking, and the ability to multitask. These tests help determine how well the client sees objects and if their perception of the location is correct.

  
  
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  Strength and range of motion: Physical characteristics of the client are measured. For each limb, strength and active range of motion are determined for the ability to operate the primary controls of the vehicle. Head rotation for scanning traffic is observed and documented. Other areas assessed include joint restrictions in neck and limbs, motor control, dexterity, and balance.

  
  
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  Reaction time to determine eye–limb coordination: Several tests are given to gather information on the potential driver’s ability to process visual information and react to it properly. Characteristics about the client’s disability are noted to determine factors such as the progressive nature of the disability and if it will impact the choice of driving equipment.

  
  
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  Cognitive issues and confidence: Other tests will provide information about the potential driver’s understanding of road signs, ability to engage in more complex driving situations, and ability to multitask. Areas observed include memory, visual processing, visual perception, visual special skills, selective and divided attention, and executive skills.

  
  
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  Driving assessment process: Once the clinical details of the driver have been established, the evaluation progresses to the vehicle assessment. Access to the vehicle is investigated, ranging from whether the driver is able to transfer from the outside of the vehicle to the driver seat, to how the driver adjusts to sitting in the wheelchair at the driver station. Numerous arrangements and adjustments within these extremes dictate the final scenario for access. Once access has been established and safety systems are in place (shoulder/lap belt), the driving controls are considered. The dominant hand is usually chosen for steering, but this may deviate if other factors or equipment are presented.

  
  
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  Driver evaluation: The potential driver is progressively given control of the vehicle. Depending on the situation, the CDRS or driving instructor may begin with the client steering in a safe environment, such as a parking lot. Eventually, the evaluation will progress to have the client also operate the gas/brake controls. They will gradually proceed onto the streets and then to even greater traffic interaction. The potential driver will be exposed to turns, controlled intersections, light and heavy traffic, and confusing situations to test their ability to respond appropriately.

  
  
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  Flexibility to test suspected capabilities: Occasionally the CDRS or driving instructor may observe a characteristic of the potential driver that indicates a lacking driving skill or a cognitive limitation. This deficiency may be the result of the client being a new driver with little experience on the road, or could indicate a larger issue that will require substantial understanding of the client’s disability and the mobility equipment used to compensate for the disability.

  
  
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  Endurance issues: Persons who have certain disabilities frequently have limitations caused by fatigue (eg, from muscular dystrophy, multiple sclerosis, or post-polio syndrome). A CDRS and driving instructor who understand a person’s disability can observe if the driver is showing signs of tiredness or lack of concentration from fatigue or extreme temperature changes. Startle responses can also impact the client’s safe driving and also should be evaluated, for example by traversing rumble strips and speed bumps.

Primary Controls

Primary controls refer to the steering, accelerator, and brake controls of the vehicle. For a disabled driver, the wheel and pedals may need to be modified to allow for weakness or limited range of motion. The control inputs may need to be relocated to a position where they can be reached. Various interfaces are used to allow a driver to have a secure connection with the vehicle. These control interfaces range from a simple spinner knob, to a yoke and T-shaped device for drivers who have grip strength, to tri-pin arrangements to allow a secure hold for drivers who have minimal grip strength.

If a driver has sufficient upper-extremity range of motion and strength, they may be able to use mechanical devices to operate the gas/brake controls. Rods and levers can be positioned so the driver’s hand can operate the pedals. Controls that use a motor to move the pedals are referred to as powered controls . The driver would operate a lever that would cause a motor to move the OEM pedals.

Another example of powered controls can be found in reduced-effort steering. The strength required to turn the steering wheel is generally reduced by 50% or 75%, which can help a driver who lacks strength in steering. In the event of engine failure (such as caused by a fan belt coming off), the steering pump would stop providing power steering and the driver would require substantial strength to turn the steering wheel. A separate pump used for backup would turn on when it senses low hydraulic pressure in the steering system. This pump would allow steering to remain operational at reduced effort long enough for the driver to pull over to a safe location. A steering backup system is also advisable for standard power steering systems for drivers who have enough strength for the OEM power steering but not enough to turn the steering wheel when the engine is off. Most devices that reduce the force needed to operate primary controls incorporate a backup system that would allow for continued reduced effort on vehicle controls when the engine fails to operate.

New advances in vehicle controls have allowed for electronic or computer interfaces to control the steering, gas, and brake. This approach can be accomplished with a two-handed system or, at the most extreme level, a joystick input. At this “drive-by-wire” stage, the operator and the vehicle have no direct link. This method incurs some degree of risk from the possibility of electrical system failure. If designed correctly, this is not as big of a concern as one might think. In fact, many commercial jets are “fly-by-wire” and have performed well. Drive-by-wire provides an opportunity to select from a wide array of control choices, including joysticks, levers, and small-diameter rotary inputs, thus permitting custom control designs appropriate for a driver’s specific needs.

This drive-by-wire technology has not been fully optimized for use in mainstream vehicles, and inherent control issues with electronic interfaces and computer controls remain. The main areas are the lag or delay in response time and the absence of sensory feedback from the road from the lack of a closed-loop system. Because of these limitations, drivers must possess above-average cognitive skills, and the training requirements to use drive-by-wire are extensive.

Secondary Controls

The primary controls are used to drive the vehicle. The secondary controls are used to manage the vehicle and interact with the elements and other drivers on the road. Operating the turn signals or shifting the transmission are some of the necessities when driving, and are examples of secondary control functions. Secondary controls are classified into three modes: A, B, and C. Turn signals, the horn, high-beam headlights, and wash/wipe functions fall into the mode A control category that is used when the vehicle is moving. Mode B controls can be operated when the vehicle is stopped and under driver control. Examples of mode B controls include transmission shifting, ignition, and vehicle startup. Mode C controls are used when the vehicle is stopped and includes the door locks, radio, hazard flashers, heater/vent/air conditioner (HVAC), light controls, mirrors, parking brake, power seats, rear accessories (defogger), and child safety window locks. Many devices are available to accommodate disabled drivers, and controls can be positioned to be operated by the elbow, by a free finger, by a mouth stick, or through voice input.

Early vehicle conversions used existing OEM switches, and attached levers and extensions to allow drivers to reach the secondary controls. These adaptations can still be used reliably, but the design of the newer vehicles precludes some previously used applications. Currently, individuals who have higher levels of disabilities are on the road, requiring a more sophisticated system to allow independent control of secondary vehicle functions. Operating a single switch with the touch of a finger or bump of the elbow can trigger a microcomputer to signal the driver to select a function, and a second action of the switch will operate the selected function. The system must match the driver’s ability and comfort level so it can be used reliably.