In an article entitled "Effects of Aging on Older Drivers' Travel Characteristics" and published in Transportation Research Record 1438, Rahim F. Benekohal, Richard M. Michaels, Eunjai Shim, and Paulo T. V. Resende reviewed the results of an Illinois statewide study focused on driving characteristics of older people. Report data suggested that, as the number of older drivers in the United States increases, older drivers' reduced visual and cognitive performance on driving-related tasks should be considered in highway safety design and operation.

According to Benekohal, et al., 12.6 percent (31 million) of the population of the United States was 65 or older in 1990; this number will increase to 21.1 percent (64 million) by 2030. Showing this trend, the number of licensed drivers age 65 and older had increased by more than 50 percent since 1969. However, highway design criteria reflect the performance characteristics of younger drivers, providing less margin of safety for older drivers.

To study travel characteristics and driving changes occurring with aging, researchers mailed a survey to 850 randomly selected drivers in Illinois over 65 years of age. Nearly 78 percent, 664 drivers, returned the completed survey. About 85 percent of respondents were 75 years or older, although only a few drivers were over 90. In addition, the research team conducted four focus groups with older drivers from both rural and urban areas to add detail to mail survey findings. In analyzing data Benekohal, et al., divided drivers into four age categories: 66 to 68, 69 to 72, 73 to 76, and 77 and older. They found some statistical differences between these categories as well as between male and female drivers. The article gave data results for nine categories:

• Travel frequency
• Road type
• Trip recency
• Trip purpose
• Trip length
• Vehicle miles traveled
• Travel time
• Conditions avoided
• Driving difficulty.

Travel Frequency: Since 70 percent of older drivers reported using their cars at least five days a week and 42 percent said they used their cars daily, survey results showed older drivers do use their cars regularly. However, as the age of the driver increased, the frequency of use decreased. Also, male drivers were more likely than females to drive a car seven days a week-- 50 percent compared to 32 percent.

Road Type: Seventy-five percent of older drivers drove mostly in a town or city, while 16 percent reported using the highways. As the age of the driver increased, urban road use increased. The authors cited examples of this tendency: "23 percent of the 66- to 68-year age group use highways compared with 7 percent in the 77+ age group, and 66 percent of the same age group compared with 78 percent of the 77+ age group drive on urban roads" (p. 94).

Trip Recency: When asked about their most recent driving trip, nearly 69 percent of males responded that they drove either that day or the day before. Only 19 percent of females said they drove that day or the day before. When asked about their second most recent trip, 49 percent said that trip had been the day before and 20 percent said it had been two days before. Results indicated about 15 percent of older drivers drove a car more than once a day. These figures helped determine average annual vehicle miles traveled for older drivers.

Trip Purpose: Forty-nine percent of survey respondents said their most recent trip was for grocery and personal shopping. Other reasons for travel were: personal business (15 percent), recreational or social trips (12 percent), going to work (8 percent), and medical or dental appointments (7 percent). Seven percent reported their trips were for more than one purpose. As driver age increased, frequency of work and recreational or social trips decreased. Frequency of grocery or other shopping trips and multipurpose trips increased with age. Also, more female drivers said their trips were for grocery and other shopping, while more males identified medical or dental appointments and recreational or social trips as their travel purposes.

Trip Length: To avoid skewing reported results, researchers computed average trip length based on a systematic deletion of extremely large trip lengths. When 95 percent of the data were used, the average trip length was 11.4 miles. The average trip length of drivers over 77 was considerably shorter.

Vehicle Miles Traveled: Researchers calculated average vehicle miles traveled based on trip length and trip frequency data reported on their survey. Correcting for extremely large trip lengths by using only 95 percent of the data, Benekohal, et al., found that the average distance survey respondents drove per year was 7,522 miles. Nearly half of the respondents felt they presently were driving less than they did ten years ago. However, 37 percent felt they were driving as much now as they did ten years ago, and 14 percent felt they were driving more now.

Travel Time: While 87 percent of older drivers said they frequently drove during off-peak hours (9 a.m. to 3 p.m.), 56 percent also drove during the afternoon peak hours of 3 p.m. to 6 p.m. Over one-fourth drove during the morning peak hours of 6 a.m. to 9 a.m. and during the evening and night hours of 6 p.m. to midnight. Less than 1 percent, however, said they drove after midnight. A significantly larger number of women than men said they drove during off-peak hours (9 a.m. to 3 p.m.).

Conditions Avoided: Saying they drove most when conditions were safest, older drivers felt they were most likely to avoid driving in snow and ice. They also avoided peak-hour travel, night driving, and driving in the rain--in that order. As driver age increased, the order changed to avoiding peak-hour traffic, ice and snow, and night driving.

Driving Difficulty: When survey respondents considered all factors to compare the difficulty of driving now with ten years ago, about 63 percent responded that driving difficulty was about the same. On the other hand, 26 percent felt driving was more difficult for them now, and only 11 percent reported driving now was less difficult. However, when researchers asked questions about such circumstances as nighttime driving or making left turns, respondents said they were having more difficulty with these specific situations than they had previously. Benekohal, et al., theorized, "They may have had to drive in more complex driving conditions (e.g., work trips) when they were younger, but now they have more freedom to select less complex driving conditions (less crowded road and off-peak hours)" (p. 96).