Relation of Driving Status to Incident Life Space Constriction in Community-Dwelling Older Persons: A Prospective Cohort Study

Abstract

Background.

Maintaining spatial movement through the environment is an important feature of healthy aging. We examined whether being licensed to drive is associated with maintaining spatial movement in older persons initially reporting maximum spatial mobility.

Methods.

From the Rush Memory and Aging Project, 571 nondemented, community-dwelling older persons were identified with (i) baseline data on driving status, (ii) baseline report of spatial mobility to the largest life space zone, and (iii) at least one annual follow-up evaluation. Incident constriction of life space was the primary outcome of interest.

Results.

Over an average follow-up of 4.3 years, 303 participants reported incident constriction of life space. In a proportional hazards model adjusted for age, sex, and education, having a valid driver's license at baseline was associated with a decreased hazard of reporting a life space constriction (hazard ratio = 0.39; 95% confidence interval = 0.29–0.54). Results were unchanged after controlling for number of vascular risk factors and vascular diseases, low visual acuity, social isolation, and gait speed. Of participants reporting incident life space constriction, 188 subsequently reported reexpansion of spatial mobility to the largest zone of life space. Having a valid driver's license was associated with a greater likelihood of life space recovery (hazard ratio = 2.00; 95% confidence interval = 1.27–3.17).

Conclusion.

In older persons, having a valid driving license was associated with reduced hazard of reporting life space constriction and a greater likelihood of life space recovery if incident life space constriction occurred.

Among licensed drivers in the United States, about 15% are persons aged 65 and older (1). More than 5000 older persons died in traffic accidents in 2009 alone (1). In order to reduce traffic fatalities in older persons, states have implemented various public policies including: mandatory in-person license renewal, vision test requirements, on-road test evaluations, and shortened license expiration time intervals. The impact on reducing traffic fatalities has been mixed. Although the traffic fatality rate among older drivers declined at a faster rate than for middle-aged drivers from 1997 to 2008 (2), a nation-wide traffic fatality analysis found an association between in-person license renewal and reduced fatality rates only among the oldest old drivers (3).

However, age-based driver license renewal policies have the potential disadvantage of reducing the spatial mobility of older persons. Research examining the association of being licensed to drive and spatial mobility in older adults without dementia is limited but suggests that having a driver’s license may be associated with higher levels of out-of-home activity (4). Although the hurdles associated with driver license renewal policies influence the decision of older persons to stop driving (5), older persons do not appear to increase their use of transportation alternatives to driving (6). A systematic review of license renewal policies for older drivers highlights the need to find balance between the benefits of preventing traffic fatalities and the potential risk of loss of spatial mobility (7).

The relationship between spatial mobility and driving status in older adults residing in an environment of more stringent licensing renewal requirements has not been fully examined, partially due to limitations of obtaining person-specific longitudinal assessments of spatial mobility. Although mobility is commonly assessed via gait skills or activities of daily living scales, these assessments do not capture the complex movement and travel of older adults (8). A life space assessment of mobility examines the spatial movement in areas extending concentrically from the location where a person sleeps to distant destinations. The life space concept recognizes that spatial mobility can be affected by many environmental and psychosocial factors in addition to ambulation and physical functioning and is not simply a proxy for mobility disability (9). Older persons reporting lower levels of life space are at risk for decline in cognitive, physical, and social function and death (10–12).

In 1989, the State of Illinois modified its already stringent older adult license renewal procedures by requiring in-person renewal with vision and on-road testing for all drivers older than 75 years along with increasing the frequency of license renewal from every 4 years to every 2 years for drivers aged 80 and every year for drivers aged 87 (13). In 1997, the Rush Memory and Aging Project (14), a longitudinal clinicopathological study of common chronic conditions of old age was initiated in the vicinity of Chicago, Illinois. As part of the study, more than 1000 community-dwelling persons without dementia had driver’s license status documented at baseline along with life space report at baseline and at each annual evaluation. As participants in the Memory and Aging Project were Illinois residents with a baseline average age older than 75 years, the study provides a unique opportunity to examine the effects of driving license status on spatial mobility in older persons exposed to more stringent driver license renewal policies. In this study, we examined the association of driving status with incident life space constriction in participants initially reporting maximum spatial mobility (ie, travel outside their town or community). As life space constriction is not inherently permanent, we also explored the association of driving status with recovery of life space in individuals experiencing life space constriction.

METHODS

Participants

All participants were older community-dwelling individuals who agreed to annual clinical evaluations and brain donation at the time of death as part of the Rush Memory and Aging Project (14). They come from about 40 groups in the Chicago, Illinois vicinity (see the Acknowledgments section). The study was approved by the Rush University Medical Center Institutional Review Board. All study participants provided written informed consent.

The Memory and Aging Project began in 1997 and rolling enrollment continues. Life space assessment was first introduced in 2001. Inclusion in these analyses required: (a) report of baseline spatial mobility to the largest life space zone; (b) absence of baseline dementia; and (c) at least one other annual assessment of life space. As of March 2009, 1239 participants had completed a baseline evaluation with 1026 enrolled following addition of the life space assessment to the clinical evaluation. Five participants were excluded for a missing baseline life space assessment along with 376 participants for not reporting baseline spatial mobility to the largest life space zone. Of the remaining 645 participants, 14 participants were excluded for having baseline dementia. Another 29 participants were not eligible for follow-up (14 persons died prior to their first follow-up and 15 had not yet reached their first follow-up) and were not included. Of the remaining 602 participants eligible for follow-up, 571 (95.0%) had one or more follow-up life space evaluations. Follow-up averaged 4.3 years (range = 0.4–7.1).

Baseline and Annual Clinical Evaluation

At baseline and follow-up evaluations, each participant underwent a uniform structured clinical evaluation that included a medical history, neurological examination, cognitive performance testing, and review of a brain scan when available. Clinical diagnoses were made using a multi-step process, as previously described (15). First, participants underwent detailed annual cognitive function testing which included 21 cognitive performance tests. Second, the cognitive test data were reviewed by an experienced neuropsychologist who determined if cognitive impairment was present. Next, participants were evaluated in person by an experienced neurologist or geriatrician blinded to all previously collected data. This physician used all available cognitive and clinical testing results from the current year’s evaluation to diagnose dementia using the criteria of the National Institute of Neurologic and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association (16). Diagnosis required meaningful decline in cognitive function from a previous level of performance and impairment in memory and at least one other cognitive domain.

Life Space

The extent of spatial movement within the environment was assessed with a modified version of the Life Space Questionnaire, a measure of self-perceived spatial movement through the environment, as previously described (8). Participants are asked to indicate whether or not they have been to a particular zone within the environment in the past week, beginning with the bedroom, and then areas immediately outside the home, in the neighborhood, outside the immediate neighborhood but in the same town or community, and finally outside the town or community. The life space score for each person is the number of zones entered, with possible scores ranging from 0 to 6. Larger scores indicate a larger life space.

Driving Status

At study baseline, each participant was asked three questions about driving. First, they were asked whether they were currently licensed to drive. Then, participants licensed to drive were asked if they had driven in the last 12 months. Finally, participants licensed to drive who had driven in the last 12 months were asked how many days during a typical week they had driven with choices ranging from less than once a week, 1 to 2 days a week, 3 to 5 days a week, or 6 or 7 days a week. The first question was used to define a participant’s driving status. The second and third questions were used to create a driving frequency variable for licensed drivers with values ranging from no driving to driving 6 or 7 days a week.

Covariates

Individuals provided date of birth, sex, and highest number of years of education completed. We computed summary scores indicating each individual's vascular risk factors (ie, the number of vascular risk factors self-reported out of hypertension, diabetes mellitus, and smoking, resulting in a score from 0 to 3 for each individual) and vascular disease burden (ie, the number of vascular diseases, out of heart attack, congestive heart failure, claudication, and stroke, resulting in a score from 0 to 4 for each individual), as previously described (14). Smoking history, heart attack, congestive heart failure, and claudication were rated as absent or present as determined by self-report; hypertension and diabetes were rated as present if the participant reported having been diagnosed with the condition or was found to be on medication for the condition, and stroke was diagnosed based on self-report plus clinical examination. Low visual acuity was defined as a best corrected near vision of worse than 20/40 using a hand-held eye chart placed 14 inches away from the participant. Social isolation was based on self-report of having a general sense of emptiness, missing having people around, not feeling as if have enough friends, feeling abandoned, and missing having really close friends. Individuals rated each item from 1 (strongly disagree) to 5 (strongly agree) where a score of 3 was neutral. Individual item scores were added together to give a score ranging from 5 to 25 with higher scores representing a greater feeling of social isolation, as previously described (17). Gait speed was derived by timing with a stop watch how long it took a participant to walk 8 feet (2.4 m) at their usual pace (18).

Statistical Analysis

Participants reporting maximum spatial mobility at baseline were divided according to whether they did or did not have a valid driver’s license. The demographic and covariate measures of participants in each group were compared using analysis of variance, chi-square tests, or nonparametric Kruskal–Wallis tests, as appropriate. We also examined baseline differences between participants reporting and not reporting life space decline on follow-up.

A discrete time proportional hazards model (19) adjusted for age, sex, and education was used to examine the association of having a valid driver’s license to the time to first report of life space constriction. For driving status, we first added a term for having a valid driver’s license. Next, we repeated the model described above with each of the following covariates added: number of vascular diseases and number of vascular risk factors, low visual acuity, social isolation, and gait speed in those who could ambulate. In a complementary analysis, we examined the association of driving frequency (for individuals who reported driving in the last year) to first report of life space constriction. We replaced the driving status term with terms for licensed participants driving one to two times a week, driving three to five times a week, and driving six to seven times a week compared with participants driving less than once a week. Finally, in order to examine whether driving status was associated with life space recovery, we used a discrete time proportional hazards model which controlled for age, sex, and education in the subset of participants reporting initial life space constriction. All models were validated graphically and analytically. Model assumptions of normality, independence, and constant variance of errors were adequately met. Analyses were carried out in SAS, version 9.1 (SAS Institute Inc., Cary, NC).

RESULTS

Baseline Characteristics of the Cohort

Of the 571 participants initially reporting maximum spatial mobility, 458 reported having a current driver’s license and 113 reported not having a driver’s license. Compared with participants with a driver’s license, participants without a current license were older (80.6 vs 78.0 years, t ⁵⁶⁹ = 3.31, p = .001), were women (86% vs 70%, χ² [1] = 12.84, p < .001), had a lower education level (13.4 vs 15.1 years, t ⁵⁶⁹ = −5.59, p≤.001), had a lower Mini-Mental State score (27.1 vs 28.4, t ⁵⁶⁹ = −6.61, p < .001), had more vascular diseases (0.4 vs 0.3, t ⁵⁶⁹ = 2.07, p < .039) but not vascular risk factors (1.2 vs 1.1, t ⁵⁶⁹ = 1.04, p = .300), had worse visual acuity (43% vs 21%, χ² [1] = 22.3, p < .001), and reported higher levels of social isolation (2.4 vs 2.2, t ⁵⁶⁹ = 3.96, p < .001). Ambulatory participants (n = 564) not licensed to drive had a lower gait speed (0.6 vs 0.7 m/s, t ⁵⁶⁴ = −7.16, p < .001).

Baseline Driving Status and Incident Life Space Constriction

Over more than 4 years of follow-up, 303 participants with maximum spatial mobility at baseline reported a subsequent reduction in their life space level. Participants who reported a life space constriction were older at baseline, had less formal education, had a lower Mini-Mental State Examination Score, reported more social isolation, had a slower gait speed, and were less likely to have a valid driver’s license (Table 1).

Table 1.

Participant Characteristics by Incident Life Space Constriction from Initial Report of Maximum Spatial Mobility

Baseline Characteristics	Life Space Maintained (n = 268)	Life Space Constricted (n = 303)	p Value
Age, mean (SD), y	76.1 (7.4)	80.6 (6.9)	<.001
Women, No. (%)	193 (46.1)	226 (53.9)	.488
Education, mean (SD), y	15.2 (3.1)	14.3 (2.9)	.001
Mini-Mental State Exam score, mean (SD), out of 30	28.4 (1.8)	27.9 (2.1)	.002
Licensed to drive, No. (%)	242 (90)	216 (71)	<.001
Number of vascular risk factors, mean (SD), out of 3	1.15 (0.86)	1.09 (0.76)	.40
Number of vascular diseases, mean (SD), out of 4	0.28 (0.54)	0.32 (0.60)	.41
Visual acuity worse than 20/40, No. (%)	62 (23)	83 (27)	.23
Social isolation, mean (SD)	2.11 (0.60)	2.33 (0.64)	<.001
Gait speed for ambulators, mean (SD), m/s	0.72 (0.20)	0.65 (0.22)	<.001

We used a discrete time proportional hazards model which controlled for age, sex, and education to examine the association of baseline driving status with incident report of life space constriction. As shown in Figure 1, participants with a driver’s license were less likely to report life space constriction (hazard ratio = 0.39; 95% confidence interval = 0.29–0.54) as compared with participants without a driver’s license.

Figure 1.

Driving status and life space. The proportion of participants reporting maximum spatial mobility as a function of time in study from a discrete time proportional hazards model adjusted for age, sex, and education level. Participants having a valid driver’s license at baseline are depicted by the solid curve and participants without a valid driver’s license are depicted by the dashed curve.

As other factors may affect baseline driving status and life space constriction, we extended our initial models four times. Each model had added terms for (i) the number of vascular risk factors and number of vascular diseases, (ii) low visual acuity, (iii) social isolation, and (iv) gait speed in ambulators, respectively. As shown in Table 2 (Models B through E), the association between baseline driving status and reduced hazard of developing life space constriction remained unchanged.

Table 2.

Relationship of Driving Status with Incident Life Space Constriction

Variable	Hazard Ratio (95% Confidence Interval)
	Model A*	Model B†	Model C†	Model D†	Model E†
Age (y)	1.08 (1.05–1.08)	1.08 (1.06–1.10)	1.08 (1.06–1.10)	1.07 (1.05–1.09)	1.07 (1.06–1.10)
Male sex	0.93 (0.69–1.25)	0.93 (0.69–1.27)	0.93 (0.69–1.25)	0.93 (0.69–1.25)	0.94 (0.69–1.28)
Education per year	0.94 (0.89–0.98)	0.93 (0.89–0.98)	0.93 (0.89–0.98)	0.94 (0.90–0.99)	0.93 (0.89–0.98)
Licensed to drive	0.39 (0.29–0.54)	0.39 (0.28–0.54)	0.39 (0.28–0.55)	0.41 (0.30–0.57)	0.42 (0.30–0.70)
Vascular risks		0.95 (0.81–1.12)
Vascular disease		1.04 (0.82–1.31)
Low visual acuity			0.98 (0.72–1.33)
Social isolation				1.34 (1.08–1.66)
Gait speed for ambulators					0.76 (0.36–1.58)

^*From discrete time proportional hazards model for time to initial report of life space constriction from maximum spatial mobility at baseline adjusted for age, sex, and education

^†From proportional hazard models which included all the terms in Model A as well as terms to control for the following covariates including: number of vascular risk factors and number of vascular disease factors (Model B), low visual acuity defined as best corrected near vision worse than 20/40 (Model C), social isolation (Model D), and gait speed in ambulators (m/s; Model E).

Finally, in a complementary model, we examined the relationship between driving frequency over the course of a week for licensed drivers and the likelihood of reporting life space constriction. Of the older licensed drivers, 33 (7.2%) reported driving less than once a week while 53 (11.6%) drove one to two times a week, 178 (38.8%) drove three to five times a week, and 194 (42.4%) drove six to seven times a week. Participants driving six to seven times a week were less likely to report a constriction in life space when compared with participants who drove less than once a week (hazard ratio = 0.46, 95% confidence interval = 0.25–0.85).

Baseline Driving Status and Recovery from Life Space Constriction

Of the 303 participants reporting incident life space constriction, 188 participants experienced recovery of spatial mobility back to the largest life space zone. In this subset of participants, we used a Cox proportional hazards model which controlled for age, sex, and education to examine the association of baseline driving status with recovery from initial report of life space constriction. Participants with a driver’s license were more likely to recover life space (hazard ratio = 2.00, 95% confidence interval = 1.27–3.17) as compared with participants without a driver’s licenses.

DISCUSSION

In this study, we examined the association of having a valid driver’s license on inter-community spatial mobility where prolonged exposure to more stringent older adult license renewal policies occurred for over a decade. In 571 community-dwelling older persons without dementia, reporting maximum spatial mobility at baseline, and followed annually up to 7 years, baseline current driving status was associated with a lower hazard of reporting incident life space constriction when compared with reporting not having a driver’s license. The findings were not due to the presence of common vascular conditions, low visual acuity, social isolation, or slow gait speed. Also, for older persons reporting incident life space constriction, having a valid driver’s license at baseline was associated with a greater likelihood of recovering spatial mobility to the largest zone of life space.

Prior cross-sectional studies have shown an association between transportation (8) and driving (9) and life space scores. However, cross-sectional studies cannot determine a temporal relationship, and our study highlights that almost 20% of community-dwelling older adults report spatial mobility to the largest life space level without having a valid driver’s license. Limited longitudinal studies have pointed to driving cessation being associated with decreased out-of-home activities (4). A novel feature of this study is the examination of the temporal relationship between driving status and loss of inter-community spatial mobility, as measured by life space, in an older cohort without dementia. Even after adjusting for potential confounders such as vascular conditions, low visual acuity, social isolation, and slow gait speed, having a valid driver’s license was associated with maintenance of life space and recovery of life space once life space constriction occurs.

We also found that participants initially without dementia who had a valid driver’s license had significant variability in their reported frequency of driving. In separate analyses of the weekly frequency of driving and incident report of life space constriction, driving six to seven times per week was associated with a lower hazard of reporting life space constriction. Our findings extend work from a cross-sectional study in persons diagnosed with mild cognitive impairment where driving frequency was associated with larger reported life space (20).

Our findings may help public policy makers better appreciate the trade-offs between traffic safety and spatial mobility that are associated with more stringent license renewal policies for older persons. To our knowledge, this study is the first to examine person-specific changes in spatial mobility in an environment where more stringent license renewal policies for older persons were enforced for almost a decade. These policies were enacted in good faith to reduce the traffic fatality rate in older persons. Although national reviews of in-person driver license renewal requirements showed a significant reduction in traffic fatality rates for the oldest old (3), the results have not been replicated in the State of Illinois (13). However, our study shows the consequences of not having a valid driver’s license. For older adults initially reporting maximum spatial mobility on the life space scale, having a driver’s license was associated with a greater likelihood of maintaining inter-community spatial mobility. As more stringent license renewal policies have been associated with the decision to not seek licensure, it may be worthwhile for policy makers to consider limiting the potential harms associated with these policies by possibly considering other factors than age including, but not limited to, driving frequency.

The mechanisms linking driving status to incident life space constriction and subsequent recovery will require further exploration. Driving is a complex task that requires integration of physical and environmental inputs. Driving status may be associated with other conditions associated with life space. Although we did not find that demographics, vascular risk factors and diseases, low visual acuity, social isolation, or slow gait speed affected our primary results, other factors may exist. Communities with more complex environments to navigate due to road design, traffic conditions, and traffic alert systems may be associated with a lower threshold for not maintaining a valid driver’s license and an increased likelihood for reporting life space constriction. Also, not maintaining a driver’s license results in reliance on other social networks or transportation services to maintain life space beyond what would be accessible by ambulation. Individuals without a driver’s license and reporting the largest life space initially may have strong networks but may be more vulnerable to future losses in their social networks. For instance, a spouse may be providing transportation to achieve maximum spatial mobility without the need for the index person to have a license; however, once the spouse dies, spatial mobility may be limited.

The strengths of our study include annual evaluations of life space and baseline questions on driving status, including frequency, which allowed us to analyze the temporal association of initial driving status and life space constriction in a large community-dwelling cohort. We also adjusted for important comorbidities associated with driving status and life space.

Our study has limitations. Although we found an association between driving status and incident report of life space constriction, we were unable to determine whether the relationship was due to the group who never had a valid driver’s license or the group who had a valid license at some point in their lifetime but decided to not renew at least 12 months prior to our baseline interview. We also did not assess the reasons for not having a valid driver’s license. We focused on the relationship between driving status and constriction of life space in participants reporting maximum spatial mobility at baseline. Future studies are needed to examine the association between driving status and spatial mobility in older persons initially reporting more constricted spatial mobility. The demographics of our population (majority white with a high education level who resided in a large metropolitan area) and the voluntary enrollment in Memory and Aging Project limit generalization to a broader elderly population. Apart from self-reported driving frequency, we did not have more detailed evaluations of driving habits of these older persons, which may have elucidated patterns in the utilization of driving to meet daily needs. Although life space provides information about spatial mobility, the scale does not provide information about whether their communities are designed to enable more efficient transportation means than driving. Further confirmation of the association between driving status and spatial mobility will be needed from studies in other longitudinal cohorts of older persons.

FUNDING

This work was supported by National Institute on Aging grant (R01AG17917) and the Illinois Department of Public Health.