Keywords

1 Introduction

The Importance of Mobility. Transportation has been identified as an Instrumental Activity of Daily Living (IADL). It is difficult to live independently without some means to leave one’s own home to shop and keep appointments (e.g., physician visits), and a lack of transportation also limits opportunities to engage in social and recreational activities. It is important to explore ways to enhance transportation opportunities throughout the lifespan. In the United States and many other nations, the automobile is the most popular and preferred form of transportation (other than perhaps walking short distances). Yet, as we age a variety of physical and cognitive changes make the driving task more difficult, sometimes resulting in the cessation of driving altogether. While driving cessation may reduce the crash risk of older adults experiencing age-related driving difficulties later in life, it is associated with its own risks. Driving cessation has been linked to higher levels of depression, isolation, and poorer health (for review, see [1]). There is strong reason to believe that multiple benefits to wellbeing and health are possible when efforts are made to ensure that older adults have access to safe transportation options.

Aging Road User Safety. Unfortunately, a variety of physical and cognitive changes occur that put aging road users (drivers, pedestrians, cyclists) at greater risk compared to their younger counterparts. One of the major factors contributing to this increased risk is increased fragility. As we age our bodies become more susceptible to damage from crash forces. A crash that injures a 20-year-old driver might kill a 90-year-old driver due to an increased risk of injury and bone fracture, and decreased ability to recover from crash injuries. Some have argued that this is the primary factor behind the increased risk of aging road users (rather than excess crash involvement [2]). However, we also know that age is associated with perceptual changes (e.g., decreased visual acuity, increased susceptibility to glare), cognitive changes (e.g., decreased visual processing speed, slower response time, decreased memory and spatial ability), and physical changes (e.g., decreased muscle strength and range of motion). These age-related changes put aging road users at greater risk for being involved in a crash and make the driving task more challenging and less comfortable (for review, see [3]). Changes in fragility and ability not only influence the safety of aging drivers, but of other aging road users as well. For example, Fig. 1 depicts pedestrian fatality rates in the United States as a function of age. There is an elevated risk for aging pedestrians, especially older men.

Fig. 1.
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Pedestrian fatality rate per 100,000 in the population as a function of age and gender (NHTSA, 2012 data).

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Safe and Accessible Transportation for an Aging Population. A variety of solutions have been explored to decrease the crash risk and increase the comfort of aging road users. One fruitful approach to reducing driver risk has been the introduction of safety features to protect vehicle occupants such as crumple zones and airbag systems. Safety features that decrease the impact of crash forces have the potential to differentially benefit older drivers and passengers who are more susceptible to these forces. This is consistent with a general trend for a decrease in the fatality risk of older drivers relative to younger drivers over the past few decades as automobiles have become safer [4].

With respect to age-related changes to perceptual, cognitive, and motor abilities, the problem can be framed in terms of a classic person-environment fit model. Each individual brings to a transportation task (e.g., making a left-turn as a driver, crossing the roadway as a pedestrian, reading and understanding a bus schedule) certain ability levels (e.g., visual acuity and reasoning ability). Each transportation task requires minimum ability levels for accurate, safe, and comfortable task performance. For example, driving requires adequate vision to detect road hazards and adequate visuospatial skills to estimate safe gaps in traffic when turning. When the abilities of the individual match or exceed the demands of the transportation task, the task can be performed safely and comfortably. However, when a mismatch occurs between the demands of the task and the abilities of the road user, safety and comfort are compromised. Unfortunately, as a result of age-related changes, there is a greater opportunity for a mismatch between the demands of the transportation task and the abilities of the aging road user. Ensuring safe and accessible transportation for an aging population requires, in part, strategies to address this mismatch and bring the demands of the transportation task and the abilities of the aging road user back into alignment. Two general strategies are available to address this mismatch; (1) change the demands of the transportation task to better match the abilities of the aging road user, and (2) change the abilities and strategies of the aging road user so that he or she can better cope the demands of the transportation task.

This paper will highlight some of the work conducted in the Aging Driver and Pedestrian Safety Lab (ADAPtS Lab), funded by the Florida Department of Transportation and the Department of Transportation supported Center for Accessibility and Safety for an Aging Population (http://utc.fsu.edu/). This research has explored ways to change the roadway to better match the abilities of road users of all ages. We also briefly review evidence that basic abilities can be modified to help older adults meet the demands of the roadway. Finally, we highlight the promise and potential pitfalls of autonomous vehicles for supporting the mobility of aging road users.

2 Changing the Roadway Environment

The Challenge of Left-Turns. Left-turns (in countries in which drivers drive on the right side of the road) in the presence of oncoming traffic can be challenging and risky, particularly when there is traffic in the opposing left-turn lane limiting the driver’s view of oncoming vehicles (Fig. 2). Left-turn crashes are a relatively severe type of crash since oncoming vehicles are typically moving fast when they strike turning vehicles. This type of crash is also particularly common and severe for older drivers [4–6], which may partly be explained by age-related declines in spatial abilities [7, 8]. Misjudging either the speed of an oncoming vehicle or its distance can result in the left-turning driver entering a gap that is too small, resulting in a crash.

Fig. 2.
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Negative offset (above) and minimal offset (below) left-turn lanes tested in a driving simulator study in the ADAPtS Lab. Note in the panel below, the white car to the left of the opposing left-turn lane is visible, while in the negative offset configuration it would not be seen.

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To help support left-turning older drivers, one potential solution is to shift opposing left-turn lanes to the right, allowing a better view of oncoming traffic (compare top and bottom panels of Fig. 2). This allows left-turning drivers more time to estimate the speed and distance of oncoming traffic. The ADAPtS Lab has used a driving simulator to investigate whether this change might benefit older drivers [9]. Younger (ages 21 to 35; N = 31), Middle-Aged (ages 50 to 64; N = 20), and Older (ages 65 and older; N = 22) drivers were asked to make a left turn in the presence of oncoming traffic. Our measure of safety was how close the nearest oncoming vehicle was when the participants’ vehicle entered the oncoming stream of traffic. Larger distances (more clearance) indicate a safer decision. In general, when drivers had a better view of oncoming traffic (minimal lane offset condition), drivers entered the intersection when the nearest vehicle was 40 feet further compared to when the opposing left-turn lane blocked more of the view of oncoming traffic (negative offset condition). This effect did not vary as a function of age, meaning that a roadway change intended to benefit older drivers benefited drivers of all ages. Changing the demands of the driving task (allowing more information to be extracted about the speed and distance of oncoming traffic) allowed for greater alignment between the demands of the roadway task and the abilities of aging road users, increasing safety.

The Challenges of Night Driving. Driving at night can be particularly challenging for older adults for a number of reasons. These include changes to the eye that result in less light reaching the retina, increased susceptibility to glare, and more time needed to dark adapt compared to younger adults [10]. These issues cause some older adults to avoid night driving altogether. Improving the visibility of signs and lane markings at night is one potential solution to increase the safety and comfort of older drivers in nighttime driving situations. The ADAPtS Lab has investigated this issue with respect to symbolic warning signs (e.g., Stop Ahead, Yield Ahead, Signal Ahead). Younger (N = 22), Middle-Aged (N = 14), and Older (N = 25) drivers were asked to identify signs in a field study by driving towards them at night, using either low or high beam settings [11]. The critical manipulation was whether the sign sheeting was standard material, or whether the sheeting was fluorescent. Fluorescent sheeting reflects back more light to the driver. A clear effect of age was observed, such that older drivers needed to be closer to the sign to identify it correctly. However, drivers of all ages benefited when the sign featured fluorescent sheeting under low beam conditions (signs could be identified about 40 feet further away compared to standard sheeting; Fig. 3). As with the left-turn study, a change to the driving task that can benefit older drivers appeared to help drivers of all ages. In fact, signs with fluorescent backing were as visible under low beam conditions as standard signs under high beam conditions. Manipulations that increase sign and lane marking visibility can partly compensate for the fact that, under low light conditions, less light reaches the retina of the older eye.

Fig. 3.
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Minimum distance at which signs could be correctly identified, as a function of headlight setting and sign sheeting material.

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Accounting for Age-Related Slowing. One of the most common findings in the literature on aging is that older adults need more time to process and respond to information [12, 13]. This has implications for various calculations related to intersection design and signal timing. For example, yellow light duration is partly based on an estimate of perception-reaction time (PRT) that assumes that one second is enough time for most drivers to perceive and react to a signal change. In a simulator study, we examined how long it would take younger and older drivers to perceive and react to signal changes from green to yellow [9]. This sample consisted of 27 younger and 25 older drivers. However, before we conducted the study, we also modeled the task of detecting and responding to a yellow signal using GOMS (Goals, Operators, Methods, and Selections Rules) modeling, with this model accounting for age-related perceptual and cognitive changes [14]. GOMS modeling predicted that older adults needed 767 ms more time to begin braking in response to a yellow signal. This was strikingly consistent with observed results in the simulator study, with older adults taking 803 ms longer to respond. Given the large difference in measured response times to yellow signals between younger and older adults, results suggest that there may be benefits to adjusting estimates of PRT to better account for age-related slowing.

The three examples presented here suggest that the roadway can be changed in ways to improve the safety and comfort of aging road users. This reduces the mismatch between the aging road users’ abilities and the demands of the transportation task. Next, we turn to two alternative approaches to reduce this mismatch.

3 Changing the Road User’s Abilities

Another approach to increasing safety and comfort is to enhance the aging road user’s abilities. There have been numerous investigations into whether or not various cognitive training programs can boost perceptual and cognitive abilities and reduce or reverse age-related cognitive decline. Some of these studies have examined outcomes related to aging road user comfort and safety (e.g., [15, 16]). While positive effects can be found in the literature, these effects are controversial [17]. A recent consensus statement signed by over 70 scientists concluded that there exist no compelling evidence that brain training programs can meaningfully improve the performance of important everyday tasks such as driving [18]. Not long after this statement was released, a counter-consensus statement was put forward, signed by over 120 scientists and practitioners, suggesting that some brain training programs are effective [19]. Given the uncertain efficacy of brain training programs at this point, they are difficult to recommend as a solution to improving the safety and accessibly of transportation for an aging population. Further, there has been no work examining the comparative effectiveness of brain training programs and other potentially beneficial programs to reduce crash risk (e.g., driver education and strategy training, on-road training).

It should be noted that crash reduction programs targeting the driving task itself often produce little observable benefit with respect to crash risk. Older driver education programs that teach strategies for avoiding risky driving situations (driving at night and during heavy traffic, making left-turns) can increase driver awareness of risk and change behaviors, but may not result in a reduction in crash rate [20, 21]. Educational programs alone may not result in reduced crash risk, but similar programs in combination with on-road training may reduce unsafe driving maneuvers [22, 23]. Results are generally consistent with the idea that specific unsafe driving situations and risky maneuvers should be targeted in order to improve aging road user safety and comfort. This strategy is consistent with theories of learning and skill acquisition that posit that the largest performance gains obtained are through practice on the task one wants to observe improvement on (near transfer).

4 The Role of Autonomous Vehicles

In the case of driving, a third general strategy to reduce the mismatch between the abilities of the aging road user and the demands of the roadway is to offload some or most of the driving task to the vehicle itself (semi-autonomous and autonomous vehicles, [24]). The potential for this strategy to increase the safety and mobility of older adults and individuals with disabilities is large. However, automation is rarely a panacea and important issues need to be considered with respect to how best to design autonomous vehicle systems, taking into account the abilities, attitudes, and preferences of aging road users, and how best to design training programs to teach drivers of all ages to use autonomous functions (see [25, 26] for designing systems and training for older adults).

No automation system is perfect, and as with any automated system in some situations a human will need to intervene [27]. Issues such as driver complacency, skill degradation, and loss of situational awareness need to be considered. Will drivers be ready to quickly regain control of the vehicle should autonomous functions fail? Will younger and older drivers be equally able to do so, given age-related changes in attention, executive control, and other age-related changes? If not, the differential risk of older drivers may persist. Other important issues to consider are factors that influence technology adoption (see [28] for factors related to the adoption of information and communications technology as an example). There is often a digital divide, with older adults adopting newer technology at a much slower pace compared to younger adults. The same is likely to be true of autonomous and semi-autonomous vehicles. Issues that influence adoption of autonomous vehicle technology (trust, perceived usefulness, perceived ease of use, price) need to be considered in order to ensure that the potential benefits of autonomous vehicles are available to drivers of all ages. There is likely to be a great deal of research into these issues (safety and usability of systems, factors influencing adoption) in the near future.

5 Conclusion and Discussion

Here we have outlined a number of approaches to help ensure the safety and mobility of the aging population. This is a critical issue as transportation is vital to independent living. Our work in the ADAPtS Lab has demonstrated clearly that the roadway environment can be changed to help accommodate age-related perceptual and cognitive changes. Left-turns become safer when drivers can extract more information about oncoming vehicles. Nighttime navigation can become easier with more visible signs. Older drivers may benefit from longer yellow light durations to account for age-related slowing. Changes such as these can help support aging drivers. However, it is also important to consider transportation more broadly, and think about additional countermeasures that specifically benefit aging pedestrians and cyclists [29, 30]. Accessible public transportation deserves attention as well. These are all important aspects of designing what the American Association of Retired Persons calls “Age Friendly Communities.” Other options are to boost the abilities of the aging road user, though this topic is controversial (particularly the effect of brain training programs on driving comfort and safety). Even if these programs are found to be beneficial, they depend upon individuals investing time, effort, and often money to complete them (compared to roadway changes that may benefit all individuals with little investment from the individual). Finally, it is likely that autonomous and semi-autonomous vehicles in the near future will play a role in reducing aging road user risk. However, as outlined previously, a number of important issues need to be addressed before this can be proposed as a complete solution to age-related risk. Moving forward it is likely that changes to the roadway, changes to the vehicle, and driver training and education all will play some role in minimizing the risk of aging road users by bringing into alignment the abilities of the aging road user and the demands of various transportation tasks.

6 Disclaimer

The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the State of Florida Department of Transportation or the U. S. Department of Transportation.