Driving

Driving has become an instrumental activity of daily living for all of us. Changes normally seen with age and the medical morbidities that occur commonly can make driving difficult, reducing human contact, social life, access to nutrition and health care, and impairing independence and the enjoyment of life. Primary prevention of loss of driving ability, secondary detection and treatment of impaired driving skills, and tertiary management of lost driving capacity are essential if driving capacity and safety are to be maintained; achievement of these goals can be challenging and time consuming in health care settings. Driving is a skill, and its loss is a social problem, which does not fit typical health care paradigms; it is obviously difficult to assess this skill in the office, especially when we all have significant time constraints. Legal and ethical questions also deter health care professionals from addressing driving. However, early intervention can prevent fatalities, injuries, unnecessary disability, and potentially the premature loss of driving skills and privileges, with their serious adverse effects on the quality of life.

CASE 1 Evelyn Harris (Part 1)

Evelyn Harris, age 74 years, comes in to your office for her annual health maintenance visit. The nurse screens her instrumental activities of daily living; Mrs. Harris reports that “It is getting very hard for me to drive at night. I don’t think it’s safe. What should I do?” She reports being blinded from oncoming headlights and having trouble clearly seeing familiar landmarks at night.

Are Mrs. Harris’s safety concerns and actions regarding driving justified?

Prevalence and impact

The number of people older than age 65 is projected to increase from 40 million in 2010 to 72 million by 2030 and 88 million by 2050, and more than 80% of this age group is licensed to drive.¹ Motor vehicle accidents are the leading cause of death from unintentional injury in those ages 65 to 74, and the second leading cause of death from unintentional injury in those older than age 75.² In 2010 almost 5500 people age 65 and older were killed (17% of all traffic fatalities) and 189,000 were injured in crashes.³ Older drivers hospitalized after crashes have significantly higher mortality rates and longer hospital stays, and are less likely to be discharged directly home.⁴ The crash risk of older adults is similar to that of those ages 24 and under, although this is mostly because of the higher risk, urban nature of their lower average number of miles traveled (referred to as low-mileage bias).⁵^,⁶ Adults over age 70 make an average of 3 trips per day, with average mileage 6400 a year; adults in their 40s take a mean 4.5 trips a day and average more than 15,000 miles a year.⁷ Older women are at higher risk of crash-related injury and fatality compared to older men; such incidents most often occur during moving violations (missing signs and signals, crossing lines while passing, and making left-hand turns). Accidents of older drivers are usually lower speed and multivehicular, reflecting city traffic.⁸ However, a larger proportion of older compared to younger adults have safe driving habits, including seat-belt use, and avoiding night driving, rush hour, bad weather, and unfamiliar areas; they also tend not to drive while under the influence of alcohol or other intoxicants.⁹

CASE 1 Evelyn Harris (Part 2)

Mrs. Harris has had no changes in her basic activities of daily living. She does report more trouble reading recently and has begun wearing her drugstore reading glasses for other activities as well. She has no chronic illnesses other than osteoarthritic changes in her hands and neck, takes an aspirin and calcium with vitamin D daily, and uses acetaminophen as needed for her neck and hand pain.

What findings do you expect on vision testing? Does Mrs. Harris have other risk factors for future driving disability and injury?

Risk factors and pathophysiology

The main medical factors affecting an older adult’s ability to drive safely are age-related loss of physical and cognitive functions, increased prevalence of medical conditions, and the use of multiple medications. Behavioral and environmental factors influence safety, but are rarely assessed with regard to their effect on driving; these factors include choice of vehicle, how often and where to drive, road and weather conditions, and distractions in the vehicle (such as eating, the radio, passengers, and cell phones), and the driver’s own values on safety versus risk.¹⁰

Physical function

Impaired vision is the most clearly identified function placing older drivers at increased risk for crashes, particularly severe visual field loss and restricted useful field of view (UFOV).¹¹ Visual field loss may be present because of glaucoma, macular degeneration, or retinopathy in 18% to 30% of those 70 and older.¹² A UFOV test takes visual processing speed and cognitive skills (such as divided visual attention) into account, by measuring speed of response to two vehicles simultaneously displayed on a monitor. If UFOV is reduced by more than 40%, the risk of motor vehicle collision increases by about 1.5 to 2.5 times.¹¹ Static visual acuity does not predict crash involvement, although it is the most commonly used measure of vision and generally the only one assessed by departments of motor vehicles. Diminished static visual acuity may decrease driving performance when lower than 20/40, particularly because of difficulty reading signage.¹³ Glare and contrast sensitivity impairment from cataract disease, present in two thirds of adults in their 70s, strongly affects driving performance and is reversible with treatment.¹⁴

The National Highway Traffic Safety Administration (NHTSA) evaluated several aspects of physical functioning measured in the Assessment of Driving-Related Skills (ADReS) published by the American Medical Association (AMA)¹⁵: the Rapid Pace Walk, and testing of manual muscle strength and range of motion (ROM).¹⁶ Motor strength testing was not found to correlate with behind-the-wheel testing. However, impaired ROM (especially the neck) and inability to walk 10 feet and back in less than 9 seconds did correlate with impaired driving skills. NHTSA guidelines summarize the available evidence for physical limitations and in particular note that any condition that affects the upper or lower limbs, the neck, and the back may have an effect on the patient’s fitness to drive.³ Arthritic conditions, common in older adults, have been associated with a twofold increase in risk for injurious crash,¹ although NHTSA notes that almost any condition may be compensated for with adaptive equipment.

Impaired range of motion of the neck and inability to walk 10 feet and back in less than 9 seconds do correlate with impaired driving.

CASE 1 Discussion

On examination, Mrs. Harris’s visual acuity has worsened from 20/70 last year to 20/100 at this visit and you see significant cataracts. She is unable to reach both hands behind her head, to touch her chin to her shoulders, or to fully close her hands. Her height has decreased by one half inch over the course of the past year. After your referral to physical therapy, her range of motion improves substantially. She also makes seat and mirror adjustments after attending a community CarFit event. Mrs. Harris’s confidence in nighttime driving activity improves after her cataracts are removed, and she returns to evening social activities.

Cognitive function

Cognitive skill is universally acknowledged to be essential for safe driving. The primary issues are which cognitive abilities can be easily and reliably evaluated and how to know which disabilities predict on-the-road driving impairment and crash risk. For example, slower speed of processing may reduce driving safety, whereas greater caution may improve it.¹⁰ Neuropsychological testing scores that reflect actual performance and are not adjusted for age or demographics better predict driving impairment and risk, because the hazards that are inherent in the road and traffic do not adjust to the driver.¹⁷ Speed and precision of visuospatial processing and attention, such as measured by the UFOV and by copying complex drawings, are key cognitive functions. The Trails Making Test–B (Trails B) evaluates processing speed, visual and motor function integration, symbol recognition and sequencing, and the ability to focus on two thought processes at once.¹⁸ Memory dysfunction appears to be an indicator of underlying neurologic illnesses impairing multiple cognitive domains, rather than an independent predictor of driving ability, because even patients with severe memory problems can perform most aspects of driving well.¹⁹ This is consistent with the characteristically much later loss of procedural memory relative to the early loss of event memory in dementias of the Alzheimer’s type. Executive decision-making is a critical function for planning and choosing what actions to perform, but this skill is not age dependent, and variability is high within age groups.²⁰

The well-known Mini-Mental State Examination (MMSE)²¹ is one of the most frequently administered cognitive screening tools to investigate impairment of the elderly (and of their ability to drive), but it was certainly not designed to assess driving skill. It focuses mainly on orientation, language, and memory, and omits the other domains of cognitive functioning important for driving competence. As such, the MMSE does not consistently predict future crashes or traffic violations.²² The Porteus Maze, Snellgrove Maze Task, Clock Drawing, Trail-Making Test Parts A or B (TMT-A, B), UFOV, and Neuropsychological Assessment Battery tests do correlate significantly with on-road driving performance.²³^,²⁴ Of these, the Clock Drawing test and TMT-B as described in the AMA’s ADReS are easily administered in the office or emergency room settings and are sensitive, identifying 92% of those who failed the behind-the-wheel test, although specificity was low at 50%.¹⁶^,¹⁸ The UFOV is commercially available. The Montreal Cognitive Assessment (MoCA) combines features of the MMSE, Clock Drawing, and Trails B, as well as testing abstract ability and verbal fluency (which tests retrieval speed), and is freely available in multiple languages. The MoCA has been found to have higher sensitivity than the MMSE for detection of early cognitive impairment, but it has not yet been studied specifically for prediction of on-the-road driving performance.^25–27 It is also important that any evaluation strategy for age-related cognitive function be applicable to measuring the functional impact on driving when one is following the course over time of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, for which the exact time of onset and speed of progression are unknown.¹⁷

CASE 2 Jerry Rucker (Part 1)

Jerry Rucker is an overweight 78-year-old man here for his quarterly checkup for his known 10-year history of hypertension, low back pain, atrial fibrillation, and mild depression. His daughter waits for you in the hall outside her father’s room so she can talk to you without her father hearing the conversation. “You have to talk to Dad about his driving when you go in. He almost got himself hit the other day, and I feel like he shouldn’t take the children out anymore.” She tells you that he has become more absentminded over the past year, sometimes forgetting to take his daily medications.

Mr. Rucker attributes this to “dizzy” spells that started a couple of months ago and occur almost every week, but never yet while driving. Although willing to admit to being “a little slower on the brakes” than he used to be, he does not recall the incident described by his daughter until half way into the story. Mr. Rucker does then admit to turning left in front of an oncoming car while attempting to beat someone else to the parking spot he wanted at his grocery store. He is upset that his daughter is no longer willing to let him drive his grandchildren to activities and thinks she is “making a big deal out of nothing.”

1. What driving skills appear to be already impaired in Mr. Rucker, and what risk factors does he have for additional driving disability and injury?

2. What additional information would be most useful?

Medical conditions and medications

Many medical conditions that are more prevalent with increasing age are associated with an elevated risk of crash, and so is the use of multiple medications (Box 35-1).²⁸ The natural history, time course, severity, stage, and treatment of a medical disorder influence its effect on driving.²⁹ Interactions of medications and medical conditions with other (often multiple) comorbidities and medications are also significant.³⁰ Medical conditions that affect driving fall into three categories: those causing (1) acute loss of function (e.g., syncope, seizure, fracture with cast), (2) chronic functional limitations (e.g., neuropathy, dementia, sleep apnea, heart failure), and (3) the use of unsafe substances (medications, street drugs, alcohol).³^,³⁰ Older adults taking any medication were 1.43 times more likely to be involved in a crash than those taking none, and those taking three or more potentially driving-impairing medications were 1.87 times at risk of a crash.³¹ In a trauma population, those on two or more central nervous system–acting medications had 7.99 times the risk of crash.³²