factors related to driving difficulty and habits in older drivers

Accident Analysis and Prevention 33 (2001) 413–421

Factors related to driving difficulty and habits in older drivers

Jacquelyn M. Lyman a, Gerald McGwin, Jr a,b,*, Richard V. Sims c,d

a Department of Epidemiology, School of Public Health, 700 S. 18th Street, Suite 609 EFH, Uni6ersity of Alabama at Birmingham,Birmingham, AL, USA

b Section of Trauma, Burns, and Surgical Critical Care, Department of Surgery, School of Medicine, Uni6ersity of Alabama at Birmingham,Birmingham, AL, USA

c Di6ision of Gerontology and Geriatric Medicine, Center for Aging, Department of Medicine, Uni6ersity of Alabama at Birmingham,Birmingham, AL, USA

d Birmingham Department of Veterans Affairs Medical Center, Birmingham, AL, USA

Received 20 December 1999; received in revised form 19 June 2000; accepted 21 June 2000

Abstract

Objecti6es: To evaluate the association between chronic medical conditions, functional, cognitive, and visual impairments anddriving difficulty and habits among older drivers. Design: Cross-sectional study. Setting: Mobile County, Alabama. Participants:A total of 901 residents of Mobile County, Alabama aged 65 or older who possessed a driver’s license in 1996. Measurements:Information on demographic characteristics, functional limitations, chronic medical conditions, driving habits, and visual andcognitive function were collected via telephone. The three dependent variables in this study were difficulty with driving, definedas any reported difficulty in ]3 driving situations (e.g. at night), low annual estimated mileage, defined as driving less than 3000miles in 1996, and low number of days (53) driven per week. Results : A history of falls, kidney disease or stroke was associatedwith difficulty driving. Older drivers with a history of kidney disease were more likely to report a low annual mileage than subjectswithout kidney disease. Low annual mileage was also associated with cognitive impairment. In general, older drivers with afunctional impairment were more likely to drive less than 4 days per week. Older drivers with a history of cataracts or high bloodpressure were more likely to report a low number of days driven per week, while subjects with visual impairment were at increasedrisk of experiencing difficulty driving as well as low number of days driven per week. Conclusions: The results underscore the needto further understand the factors negatively affecting driving independence and mobility in older drivers, as well as the importanceof improved communication between older adults and health care professionals regarding driving. © 2001 Elsevier Science Ltd.All rights reserved.

Keywords: Activities of daily living; Aged; Automobile driving; Epidemiology; Health status; Odds ratio

www.elsevier.com/locate/aap

1. Introduction

In the US, the most common method of travel forelderly people is driving an automobile (Federal High-way Administration, 1995). As this segment of thepopulation continues to increase, so does the concernfor the safety of these drivers. Older drivers have one ofthe highest automobile crash rates per mile traveled ascompared with most other groups (Williams andCarsten, 1989); they also drive fewer miles, make fewertrips, and drive less in certain situations (e.g. nighttime,

during rush hour) (Chu, 1990). This reduction in driv-ing and changes in driving behavior patterns has beenattributed to the absence of work related mileage, otherlifestyle changes, and the recognition of decreased driv-ing performance (Rosenbloom, 1988; Bly, 1993; Stutts,1998; Burns, 1999). The effect of these factors on theelderly population is a reduction in mobility, which is amajor contributor to their well-being (Carp, 1988).

The primary focus of research on driving decisionsmade by older persons has been the cessation of driving(Stutts, 1998). The reasons behind the decision to stopdriving most commonly given by older persons are alack of comfort driving or loss of confidence in theirdriving abilities, vision problems, or health problemsother than vision (Wallace and Colsher, 1991; Persson,

* Corresponding author. Tel.: +1-205-9753036; fax: +1-205-9753040.

E-mail address: [email protected] (G. McGwin, Jr).

0001-4575/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.PII: S 0 0 0 1 -4575 (00 )00055 -5

J.M. Lyman et al. / Accident Analysis and Pre6ention 33 (2001) 413–421414

1993; Kington et al., 1994). However, driving cessationlies at the end of a continuum leading from completedriving independence to driving cessation. Few studiesto date have evaluated the characteristics that propelthe older driver along this continuum. There is increas-ing attention on the influence of different medical con-ditions on driving, performance. Dementia (Fitten etal., 1995; Trobe et al., 1996; Lundberg et al., 1997),visual impairment (Johnson and Keltner, 1983; Owsleyet al., 1998a,b), and chronic medical conditions (Gres-set and Meyer, 1994; Koepsell et al., 1994; Marottoli etal., 1994; Hemmelgarn et al., 1997; Sims et al., 1998)have been found to be associated with automobilecrashes in the elderly. The effect of medical conditionson an older driver’s current driving patterns (e.g. driv-ing frequency and avoidance strategies) is also of greatinterest. Prior research suggests that medical and func-tional impairment may be associated with driving, pat-terns in older adults (Forrest et al., 1997; Stutts, 1998),however, the specific effects of certain conditions re-main to be evaluated.

The objective of this study was to evaluate the associ-ation between specific chronic medical conditions andfunctional, cognitive, and visual impairments and re-duced mobility and driving difficulty among olderdrivers.

2. Methods

2.1. Study design and study subjects

The subjects in this study were originally assembledas part of a case control study of automobile crashesand medical/functional impairments in the elderly. Thedetails of the study methodology have been described indetail elsewhere (McGwin et al., 1999). Briefly, thepopulation base for this study included all residents ofMobile County, Alabama, aged 65 and older, whopossessed a driver’s license. Case subjects were definedas those who had been involved in at least one automo-bile crash between 1 January 1996 and 31 December1996. Controls were non-crash involved drivers. Datatapes supplied by the Alabama Department of PublicSafety (DPS) were used to enumerate the study base(i.e. cases and controls).

Of the potential study subjects with an identifiedtelephone number (N=3027), a sample of 1173 sub-jects were randomly selected to be inter-viewed. Nine-hundred and one (76.8%) participated, 172 (14.7%)refused to participate, 59 (5.0%) could not complete theinterview because of an impairment, and 42 (3.6%) weredeceased at the time of the interview. Participants didnot differ from non-participants with regard to eitherage or sex.

2.2. Data collection

Data was gathered via telephone interviews bytrained interviewers blind to the study hypotheses. In-formation was collected on demographics (age, sex,race, marital status, education), functional impair-ments, chronic medical conditions, driving habits, andvisual and cognitive function.

2.2.1. Functional limitationsSubjects were asked if they had difficulty with or

required help with any of the following activities: mov-ing outdoors, using stairs, walking at least a quartermile, carrying a heavy object 100 yards, walking be-tween rooms, feeding oneself, getting in and out of bed,using, the lavatory, dressing and undressing, and wash-ing and bathing oneself.

2.2.2. Chronic medical conditionsSubjects were asked whether a physician, nurse, or

other health care professional had ever told them thatthey had any of the following conditions: arthritis,cancer, cataracts, diabetes, glaucoma, heart disease,high blood pressure, kidney disease, and stroke, as wellas any other medical conditions not explicitly men-tioned. Subjects were also asked if they had experiencedany falls or were currently using a hearing aid.

2.2.3. Dri6ing habitsInformation collected on driving habits included self-

reported quality of driving, estimated annual mileage,number of days per week driven, driving speed com-pared with the general flow of traffic, and level ofdifficulty with certain driving situations: at night, infog, in the rain, while alone, during rush hour, on thehighway/freeway, with children, in high density traffic,when passing other cars, when changing lanes, whenmaking left hand turns at intersections, and parallelparking.

2.2.4. Visual functionA modified version of the National Eye Institute

Visual Functioning Questionnaire (NEI-VFQ Phase 1Development Team, 1995) was used to assess visualfunction. Subjects were presented with a variety ofactivities (e.g. reading a newspaper) and questioned asto how much difficulty they had doing- these activities(Phase, 1995). Responses were aggregated into threescores for specific types of vision (near vision, farvision, peripheral vision), each ranging from 0 to 100.Subjects with scores 575 were defined as impaired.

2.2.5. Cogniti6e functionA version of the Short Portable Mental Status Ques-

tionnaire (SPMSQ) for telephone administration wasused to assess cognitive status (Pfeiffer, 1975; Roc-

J.M. Lyman et al. / Accident Analysis and Pre6ention 33 (2001) 413–421 415

caforte et al., 1994). Cognitive impairment was definedas three or more errors on the SPMSQ.

2.3. Statistical analysis

The three dependent variables of interest in this studywere high level of difficulty with driving, low annualestimated mileage, and low number of days driven perweek. Subjects were deemed to have a high level ofdifficulty with driving if they reported any difficulty inthree or more of the previously mentioned drivingsituations (e.g. at night). Subjects were considered tohave low annual mileage if they reported driving lessthan an estimated 3000 miles in 1996. Subjects with alow average number of days driven per week were thosewho reported driving an average of 3 or less days aweek. Low annual mileage and low number of daysdriven per week were used as indicators of reduceddriving mobility. Subjects not categorized as havingdriving difficulty, low mileage, or low days were used ascomparison groups for each of the three dependentvariables. Subjects who reported having stopped driv-ing prior to 1 January 1996 were excluded from theanalysis.

Frequency distributions were calculated for all vari-ables including demographic and driving characteris-tics, functional activities, medical conditions, andcognitive and visual impairments. Crude odds ratios(ORs) and 95% confidence intervals (CIs) were com-puted for demographic and driving characteristics andfor each of the three dependent variables. For func-tional activities, medical conditions, and cognitive andvisual function, ORs and 95% CIs were calculated andadjusted for age, sex, and race using separate logisticregression models for each dependent variable.

3. Results

Table 1 presents the driving characteristics of thestudy subjects. Nearly 20% of the subjects reporteddriving three or less days during the week, while morethan half of the subjects (54.1%) reported driving 7days a week. Approximately 13% of subjects estimatedtheir annual mileage to be less than 3000 miles; almosta quarter of the study population reported an annualestimated mileage of 20 000 miles or greater. The twomost common driving situations subjects reporteddifficulty with were driving in the rain (45.1%) anddriving in fog (35.3%). The least commonly reportedsituations subjects reported difficulty with were drivingalone (5.0%), making left hand turns at intersections(5.5%), and driving with children in the car (5.7%).Approximately 30% of subjects experienced a high levelof driving difficulty by reporting three or more drivingsituations.

Table 2 presents the distribution of demographiccharacteristics and selected driving characteristics of thesubjects, as well as their association with the threedependent variables of interest. Subjects with lowmileage were 70% (95% CI, 1.2–2.5) more likely to benon-white, while subjects with high difficulty and lowdays were approximately 35% more likely to be white.Females were more likely to be classified as havingdifficulty with driving as well as reduced mobility.Compared to those with less than 12 years of educa-tion, subjects with 12 or more years were more likely toexperience difficulty with driving, but less likely to becategorized as low mileage or low days. Overall, themajority of subjects reported the quality of their drivingas good (46.4%) or excellent (39.9%). Subjects with lownumber of days driven and difficulty driving were muchless likely to report the quality of their driving asexcellent than their comparison groups. They were alsoless likely to have been involved in a crash in 1996.When asked about their driving speed compared to thegeneral flow of traffic, a preponderance of the subjects(76. 1%) reported that they drove about the same speed.

Table 3 presents the functional activities, medicalconditions, and cognitive and visual status of the studypopulation. Subjects with driving difficulty were 1.3-times (95% CI, 0.9–1.9) more likely to report problemscarrying heavy objects at least 100 yards. This associa-tion, though of borderline statistical significance, re-mained after adjusting for age, sex, and race (OR 1.3[95% CI, 0.9–1.9). For low mileage subjects, adjusted

Table 1Driving characteristics of study population

Number PercentDriving characteristics

Days per week usually dri6en153 18.8532204–6 27.1

7 440 54.1

Annual miles dri6enB3000 110 12.6

2683000–9999 30.6294 33.610 000–19 999203]20 000 23.2

Dri6ing situationsDriving in the fog 381 45.1Driving in the rain 296 35.3

177Driving in high density traffic 21.4Driving during rush hour 169 20.2

167Driving at night 19.788Parallel parking 11.068Changing lanes 8.264 7.7Passing other cars59 7.1Driving on the highway/freeway

5.748Driving with children in the car45 5.5Making left hand turns at intersections41 5.5Driving alone

29.3250Difficulty with ]three driving situations


Table 2Crude odds ratios (ORs) and 95% confidence intervals (CIs) for association between demographic and driving characteristics and driving patterns

Low mileagea OR (95% CI)High difficultya OR (95% CI) Low daysa OR (95% CI) Total N (%)

DemographicAge (years)65–69 1.0 1.0 1.0 258 (29.5)

1.0 (0.7, 1.6) 2.5 (1.5, 4.2)0.9 (0.6, 1.3) 214 (24.5)70–721.1 (0.7, 1.6) 1.9 (1.1, 3.3) 219 (25.0)73–77 0.9 (0.6, 1.4)1.5 (1.0, 2.3) 3.1 (1.8, 5.3) 184 (21.0)0.7 (0.5, 1.1)78–99

RaceWhite 1.01.0 1.0 677 (77.4)

1.7 (1.2, 2.5) 0.7 (0.4, 1.1) 198 (22.6)0.6 (0.4, 0.9)Non-white

Sex1.0 1.0Male 432 (49.4)1.01.9 (1.4, 2.7) 3.0 (2.0, 4.4) 443 (50.6)2.2 (1.6, 3.0)Female

Marital statusMarried 1.01.0 1.0 564 (64.8)

1.5 (1.1, 2.0) 1.3 (0.9, 1.9) 306 (35.2)1.0 (0.7, 1.3)Not currently married

EducationB12 years completed 1.01.0 1.0 253 (29.4)

0.9 (0.6, 1.3) 0.6 (0.4, 0.9)1.3 (0.9, 1.9) 291 (33.8)12 years completed1.4 (1.0, 2.1)\12 years completed 0.7 (0.5, 1.1) 0.4 (0.3, 0.7) 318 (36.9)

Dri7ingQuality of dri6ingExcellent 1.01.0 1.0 343 (39.9)

1.4 (1.0, 2.0) 1.6 (1.1, 2.4)2.0 (1.4, 2.8) 399 (46.4)Good1.3 (0.8, 2.2) 1.8 (1.0, 3.1)Average/fair/poor 117 (13.6)2.6 (1.7, 4.1)

Speed compared to traffic flowAbout the same 1.01.0 1.0 648 (76.1)Slower 1.3 (0.8, 1.9)1.4 (1.0, 2.0) 1.4 (0.9, 2.2) 160 (18.8)

0.4 (0.2, 1.1) 0.2 (0.1, 1.0)0.9 (0.4, 1.8) 44 (5.2)Faster

In6ol6ed in a crash in 1996 0.8 (0.6, 1.1)0.9 (0.6, 1.2) 0.7 (0.5, 1.0) 431 (49.3)

a See Section 3 for definition.

ORs for difficulty with carrying heavy objects at least100 yards (OR 1.2 [95% Cl, 0.8–1.8]), using the lava-tory (OR 1.3 [95% CI, 0.1–12.4]), dressing and undress-ing (OR 1.7 [95% CI, 0.6–5.2]), and washing andbathing yourself (OR 2.5 [95% CI, 0.8–7.6]) were ele-vated but not significant. Several functional activitiesdemonstrated significant associations with low numberof days driven per week after adjusting for demo-graphic factors. Subjects reporting low days were morelikely to report difficulty with using stairs (OR 1.8 [95%CI, 1.0–3.1]), walking at least a quarter mile (OR 1.8[95% CI, 1.1–3.1]), or feeding themselves (OR 6.6 [95%CI, 1.2–37.8]). A number of borderline significant asso-ciations were also observed; low days subjects were 1.5-(95% CI, 1.0–2.4) and 2.8- (95% CI, 0.9–8.4) timesmore likely to report difficulty carrying a heavy objectat least 100 yards or walking between rooms, respec-tively. Adjusted ORs for difficulty moving outdoors(OR 1.7 [95% CI, 0.7–3.7]) and dressing and undressing

(OR 2.4 [95% Cl, 0.8–7.4]) were also elevated but notsignificant.

Subjects with driving difficulty were more likely tohave suffered a fall (OR 1.7 [95% CI, 1.1–2.8]), stroke(OR 1.7 [95% CI, 0.9–3.2]), or have kidney disease (OR2.8 [95% CI, 1.4–5.5]); low mileage subjects were also(OR 1.8 [95% CI, 0.9–3.7]) more likely to report kidneydisease. Low days subjects were 30% more likely toreport cataracts (95% CI, 0.9–2.0) and high bloodpressure (95% CI, 0.9–1.9).

Subjects with driving difficulty were significantlymore likely to have near vision impairment (OR 2.2[95% CI 1.4–3.4]). Subjects with low annual mileagewere more likely to be cognitively impaired (OR 1.3[95% CI, 0.9–1.9]) and have far vision scores 575%(OR 1.3 [95% CI, 1.0–1.9]). Low days subjects were1.6-times (95% CI, 1.1–2.4) more likely to have a farvision score 575 and 50% (95% CI, 0.9–2.7) morelikely to have a near vision score 575%.


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4. Discussion

The goal of this study was to evaluate the associationbetween medical and functional impairments and driv-ing habits and patterns. The results suggest that olderadults with driving difficulty are more likely to havesustained a fall, have kidney disease, or near visionimpairment. There was also an increased risk of drivingdifficulty associated with difficulty carrying heavy ob-jects and stroke, though these associations were ofborderline significance. Subjects reporting low annualmileage were more likely to have kidney disease, cogni-tive impairment, and far vision impairment; only thelatter of which met formal statistical significance. Driv-ing three or less days per week was associated withseveral functional impairments (difficulty using stairs,walking at least a quarter mile, carrying a heavy object,feeding one’s self) and far vision impairment. Severalother characteristics (walking between rooms, dressingand undressing, cataracts, high blood pressure, nearvision impairment) were also associated with reducedmobility but not significantly so.

The majority of studies on the driving habits of olderadults have focused on driving cessation (Stutts, 1998).Older adults frequently attribute the decision to stopdriving to health problems (Carr, 1993; Johnson, 1995;Forrest et al., 1997); this has also been supported byempirical research (Kington et al., 1994). A variety ofother intrinsic and extrinsic factors also appear to playa role (Persson, 1993). Among those who remain be-hind the wheel, research indicates that the driving pat-terns of older adults differ from those of young andmiddle-aged drivers (Benekohal et al., 1994; Eberhard,1996). The reason for the differences can be partlyattributed to lifestyle differences; that is, retirementremoves the need to commute to work and increasesflexibility in terms of when trips are made (Rosen-bloom, 1988; Chu, 1990; Burns, 1999). Also of interestis the fact that older drivers report difficulty withspecific driving tasks (e.g. driving at night) (Chu, 1990;Persson, 1993; Benekohal et al., 1994; Forrest et al.,1997). To date, few studies have evaluated the charac-teristics associated with changes in driving habitsamong older adults, while focusing instead on factorsassociated with driving cessation. Such research hasimportant implications for the older driver, particularlyif research suggests that modifiable risk factors areassociated with changes in driving. For example, thatloss of visual acuity resulting from cataracts is associ-ated with driving restriction and/or difficulty may meanthat cataract surgery would increase mobility andindependence.

The association between vision impairment and driv-ing habits was not unexpected. A number of studieshave also reported associations between vision anddriving characteristics (Ball et al., 1998; Stutts, 1998;

Gallo et al., 1999). Stutts reported that the prevalencevisual impairment was significantly higher among olderadults who drove less than 3000 miles annually andamong high risk avoidance drivers (Stutts, 1998). Twoother studies reported similar findings (Ball et al., 1998;Gallo et al., 1999). It is likely that older drivers, awareof the problems they are experiencing with their vision,decrease the amount of driving or refrain from drivingin certain situations. The possibility that older driversrecognize their own driving difficulty and modify theirdriving to accommodate this fact is encouraging (Ball etal., 1998). Older drivers, faced with declining visualfunction, may feel that certain driving tasks (e.g. driv-ing alone or at night) may put them at an increased riskof being in a crash or simply make them uncomfortableand thus, alter their driving tasks to avoid such situa-tions. These findings may also be partly explained bythe cautious nature of some older adults and theirability to regulate when and where they drive. Thus, thepromotion of self-regulation as a method for improvingsafety among older drivers with visual impairmentsneeds to be assessed as an intervention. However, suchregulation is likely to come at the expense of mobilityand independence. Further, it remains to be seenwhether such self-regulation is, in fact, associated withsafer driving (i.e. lower crash rates). If this is true, theninterventions to promote self-regulation would be at-tractive and could be targeted towards those with thegreatest difficulty (i.e. visually impaired). However, forcertain groups of older drivers, it may also be possibleto actually improve mobility and safety and reducedriving difficulty. Therefore, interventions to improvevisual function (e.g. cataract surgery) represent an op-portunity to modify those factors that motivate theolder driver to stop or reduce their driving, particularlyin certain situations. Interestingly, we also found thatsubjects reporting a history of cataracts were morelikely to report driving three or fewer days per week. Interms of driving cessation, there are inconsistent find-ings with regard to cataracts. Marottoli et al. foundthat cataracts was associated with driving cessation(Marottoli et al., 1993), while Campbell et al., foundcataracts to be unrelated to the decision to stop driving(Campbell et al., 1993). It may be hypothesized thatsome older adults reduce their driving with the progres-sion of cataracts and, having adapted their driving,maintain these new driving patterns after surgery. Fu-ture studies should attempt to evaluate changes indriving habits following cataract surgery as this treat-ment option has the possibility of improving the qualityof life for the older driver with respect to vision andmobility.

The finding that cognitive impairment was associatedwith low mileage is encouraging given the associationbetween dementia and crash risk (Stutts et al., 1998). Anumber of other studies have also reported positive


associations between cognitive impairment and drivingreduction and restriction (Stutts, 1998; Gallo et al.,1999). However, the low magnitude of these associa-tions and the lack of an association with other drivinghabits (e.g. difficulty) in the present study suggest thatconcern is still warranted. While many other adults areable to recognize their declining function and modifytheir behavior. However, for some, particularly thosewith cognitive impairment, this may not be the case andthe intervention of physicians may be necessary. Fortu-nately, research suggests that physicians can be influen-tial in the decision to modify driving behavior (Stutts,1998). Geriatricians and other health professionalsshould counsel patients with cognitive impairment tomodify their driving behavior or refer them to drivingassessment professionals for evaluations of driving, vi-sual, and cognitive skills.

Our results indicated that a number of chronic medi-cal conditions were associated with driving habits. Sub-jects who sustained a fall were more likely to reportdifficulty driving. Consistent with our findings, Forrestet al. reported that a history of falls or fractures wasassociated with decreased mileage (Forrest et al., 1997).This finding is likely a reflection of factors that influ-ence fall risk (e.g. cognitive impairment, poor vision),as well as sequella that result from the fall. Educationand utilization of methods to reduce falls and enhancea return to function following a fall would potentiallyincrease the overall mobility of older drivers. Subjectswho had experienced a stroke were also more likely tohave difficulty with driving. While prior studies havenot found a significant association between stroke anda change in driving patterns among older drivers, anumber of studies have found stroke to be associatedwith the cessation of driving (Campbell et al., 1993;Marottoli et al., 1993; Stewart et al., 1993). Thus, whilesome stroke-survivors radically change their drivinghabits there are some who resume driving but withdifficulty. Given the heterogeneous outcomes of stroke-survivors it is not remarkable that some stroke patientswould cease driving while others would continue driv-ing but with difficulty. Recent research has suggestedthat many stroke patients do not receive informationregarding driving from physicians or rehabilitation pro-fessionals (Fisk et al., 1997). This underscores the needfor programs to ensure that stroke survivors receiveappropriate advice about driving and driving evalua-tions to provide patients and family with accurateassessments of driving skill. The results also indicatedthat subjects with kidney disease were more likely toreport difficulty with driving, as well as reducedmileage. One possible explanation for this finding isthat patients with kidney disease are also more likely tohave other associated comorbidities and that this asso-ciation represents a surrogate for overall health statusor another specific condition. However, when adjusting

for other medical conditions, the association betweenkidney disease and both outcomes persisted. This find-ing requires further investigation.

Functional impairments were associated with lownumber of days driven per week. Gallo et al. also founda relationship between functional status (i.e. mobility,upper extremity activities) and adaptation of drivingbehavior (Gallo et al., 1999), while others have reportedassociations between activities of daily living and driv-ing cessation (Campbell et al., 1993). Another studyreported that the impaired ability for self-care, but notother functional impairments, was associated with areduction in driving in men (Colsher and Wallace,1993). The findings of this study correspond to theresults of the present study where certain impairedself-care abilities (e.g. feeding yourself) were stronglyassociated with the low number of days driven perweek. We observed associations between functional im-pairment and driving frequency but not with drivingdifficulty; a finding recently reported by Gallo et al.(1999). According to Gallo et al., drivers who adapttheir driving may be at an intermediate stage in relationto the development of functional impairment (Gallo etal., 1999). Another possible explanation is that thereduced frequency is coupled with driving tasks that donot exceed driving skills.

When interpreting the results of this study, severallimitations should be kept in mind. All the informationwas obtained through self-report. Self-reported healthstatus is of particular concern as subjects may be un-willing to disclose this information or misunderstand orforget the diagnosis. Any resulting bias would be to-wards the null since misclassification of the independentvariables would not be expected to be differential be-tween subjects with high difficulty or reduced mobilityand their comparison groups. Nevertheless, severalstudies have demonstrated an excellent agreement be-tween self-report and medical record diagnosis of thecondition; therefore, any effect on the estimate of theassociation is likely to be negligible (Colditz et al., 1986;Bush et al., 1989; Midthjell et al., 1992; Bowlin et al.,1993; Heliovaara et al., 1993; Haapanen et al., 1997).Also, at least one study has reported good agreementbetween self-reported and actual driving behaviors(Murakami and Wagner, 1997).

In summary, the current study found that a historyof falls, kidney disease or stroke among older driverswas associated with difficulty driving, while those withfunctional impairments demonstrated low number ofdays driven per week. Older drivers with visual impair-ment are at increased risk of both driving difficulty andlow number of days driven per week. Interventions thatcould potentially improve older adults overall mobilityinclude education on prevention of falls and assistancewith determining ways to compensate for functionalimpairments. The results of this study underscore the


need for further research regarding the factors nega-tively affecting driving independence and mobility inolder drivers as well as improved communication be-tween older adults and health care professionals regard-ing driving.

Acknowledgements

This study was made possible by the Center forAging Intramural Grant Program and the Center forResearch in Applied Gerontology at the University ofAlabama at Birmingham. We would like to thank DrLea Vonne Pulley and Dr Jeffrey M. Roseman for theirassistance in the design of this project.

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