What choice would you make?

It is cold and clear, but the weather report calls for mid-morning clouds and icy rain. You have a number of things to pick up before your lunchtime appointment. You could walk the two blocks to the bus stop, waiting in the cold, transfer to another bus and prepare to carry bundles back the same route on your way home. Or, you could take your car. The choice is obvious, right? But, for many of us, the still-bright sky will begin to appear less friendly as we squint into the sun's glare and begin to worry if we can get home before the sleet falls.

Vision, Age, and Driving

Both our safety and comfort level behind the wheel have become the focus of research directed at the questions of how and to what extent aging compromises safe driving, and in what ways aging vision contributes to such changes. A variety of functions, including our sensory abilities, the speed and timing of our psychomotor responses, memory, vigilance and attention, interact with driving conditions--traffic level, time of day, and so forth--to play a vital role in driving performance.

Changes with age in both acuity--the ability to distinguish fine detail--and contrast sensitivity--measured by our ability to detect targets of varied size when they are low in contrast relative to their background--reduce our capacity for gathering the information in our driving field necessary for making prompt and correct judgments in moving traffic. Typically, eye exams for driver licensing test our vision under optimal conditions. The high-contrast targets on the eye chart are motionless, directly before us and viewed under good, non-glare lighting. Yet, we know that low-contrast target movement, especially high-speed movement, and low light levels are particularly taxing for the older visual system. Further, the extent of our useful visual field of view diminishes, making it necessary to turn our heads further, and perhaps more frequently, to appreciate the changing traffic conditions around us.

The problems associated with low light during the evening and nighttime hours often impose constraints on the nighttime activities of older drivers, many of whom reduce their level of night driving, choosing to stay home instead. What contributes to the difficulties that we experience with low levels of light as our eyes age?

First, the pupil, the opening behind the cornea which allows light to enter the eye, becomes gradually smaller. In addition, the lens of the eye becomes more opaque. As a result of these changes, by the age of 60, the retina receives only about 1/3 as much light as when we were 20. In addition to its increased opacity, the lens loses most of its capacity to adjust its focus on near displays, such as the car's instrument panel. This problem is exacerbated at lower light levels. Changes in the lens also increase light scatter, in turn, increasing our susceptibility to glare, including that caused by oncoming headlights as well as that due to reflection in our rear-view mirrors from night traffic behind us.

Improved Guidance for Night Driving

Nighttime driving, which is less safe than daytime driving regardless of driver age, is particularly challenging for many older drivers because our eyes need more and more light to yield equal visibility. Presumably, this problem contributes to the reduction in night driving by older drivers that has been reported in many studies. Insufficiently lit roads are particularly likely to curtail our willingness to navigate at night, thus diminishing our mobility and independence. There are many ways, however, to increase road visibility, and therefore safety and comfort level on the road, day or night.

A very important element in safe night driving is adequate roadway guidance. So, traffic safety engineers have been evaluating promising advances which may help to decrease safety risks that the population of older drivers especially are likely to experience, particularly at night. Better and more extensive guidance using special lighting devices are among these positive changes; so, too, are wider, more reflectant roadway striping and markers. On some highways, raised reflective pavement markers are being installed in the road itself. They contribute to nighttime lane visibility by capturing the light from your headlights and reflecting it back to you. The visual information they provide can "communicate" the layout of the road, its curves and turns, as far as 1,000 feet ahead. Other advantages to this type of marking are that they delineate lane lines clearly and brightly at night, dusk, or in the rain, both for parallel and on-coming traffic; they can also warn you if you drift from your lane by causing a slight bump as you do so.

In addition to improvements in roadway marking and lighting, automotive and traffic engineers are developing more effective visual displays for cars and along roadways. The use of larger, brighter letters or symbols on signs, with high contrast between the figures and background on which they appear, can help compensate for some of the visual decline that we experience with age. Bright lighting for instrument panels with a large user-adjustable range also seems to help.

Our Best Safeguard Against Risk

Knowing what to expect as we age, especially how the various abilities on which driving depends change, is important to our ability to use good judgment about driving. If we must change our driving habits, we are more willing to do so if we understand the underlying reasons, including how they relate both to our own safety and that of others. Beyond such actions as driving at off-peak hours and avoiding unnecessary trips in darkness, under adverse weather conditions, or during rush hour, there are a number of things that we can do to increase both safety and comfort behind the wheel:

• Have regular medical and eye exams; if you wear glasses, have the prescription checked regularly and up-dated, if necessary;
  
• Keep all glass surfaces clean inside and out: your eyeglasses, car windshield, and all windows and mirrors;
  
• At night, set your rear-view mirror to the "night setting" to reduce glare from the lights of following cars;
  
• As oncoming vehicles draw near at night, look ahead toward the right side of the road to help reduce the glare from their headlights;
  
• Keep a good flashlight handy for reading signs, maps, and house numbers after dark.
  
• Before heading for an unfamiliar destination at night, it might help to make a "preview" trip during daylight hours. Finding someone to go along as "navigator" can also reduce the demands of driving in unfamiliar areas or in high-traffic conditions;
  
• You might consider installing oversize side mirrors, which will help compensate somewhat for reductions in visual field or neck/trunk flexibility.