In a presentation to the January 1994 Transportation Research Board Annual Meeting, authors Robert E. Dewar, Donald W. Kline and H. Allen Swanson address the problems associated with aging and traffic sign comprehension in their paper, "Age Differences in the Comprehension of Traffic Sign Symbols." Their report confirms what previous research has shown: older drivers have poorer understanding of traffic symbols than younger drivers do.

The dramatic increase in the numbers, as well as the proportion, of elderly (typically defined as those over 65) people in the U.S. that has occurred over the past few decades will continue for some time to come. Data indicates that the percentage of people in the U.S. over 70 who had driver licenses doubled from the early 1950s to 1984. The proportion of older drivers will continue to increase, as people in our society are very dependent on personal transportation and are unlikely to give up readily the use of their automobiles. In addition, it has been shown that miles driven annually by older drivers have increased. As a result of these changes, interest in the problems of elderly road users has grown dramatically.

In the research for this study, Dewar et al examined comprehension levels of virtually all (85) of the symbols in the U.S. Manual on Uniform Traffic Control Devices as a function of age. New versions of 13 of these symbols, as well as 5 "novel" symbols, were also tested. Drivers in Texas, Idaho, and Alberta, Canada, participated in the studies.

There has been a great deal of research done on traffic signs, but little is known about their effectiveness for older drivers. Driver age has been a variable of concern in a few studies of sign comprehension, legibility distance, and sign luminance requirements; but a systematic examination of the issue with a large sample of subjects and a wide variety of traffic sign symbols has not been carried out to date. The authors document several traffic sign studies that have been conducted, but none of them examine very extensively the significance of driver age in relation to sign comprehension. There is clearly a need, as the authors contend, for a systematic and comprehensive evaluation of drivers' understanding of the symbols used on highway signs in order to know where best to concentrate efforts to improve them.

The objective of this study was to evaluate the level of comprehension of virtually all the symbolic highway signs in the U.S. Manual on Uniform Traffic Control Devices among young, middle- aged, and elderly drivers. The specific study described here is one of a larger set of studies that examined not only symbol comprehension; but also visibility distance under day, night, and night-with-glare conditions, reaction time, glance legibility, and conspicuity. It was conducted in two phases.

Phase 1

Four hundred and eighty volunteer licensed drivers, aged 18-88, were solicited from existing subject pools, driver licensing offices, local service clubs, recreational/social organizations for senior citizens, newspaper adds, and personal contact by the experimenters. The stimuli were 85 color slides of traffic sign symbols in the U.S. Manual on Uniform Traffic Control Devices. Test booklets consisting of 19 pages were used for subjects to provide information about their driving backgrounds and to write their responses for each of the signs. The subjects' task was to view signs shown for 30 to 40 seconds each and to write in the meaning of each sign.

On the basis of correct responses, it is evident that many symbols are very well understood. On the other hand, several are poorly understood. Those which were understood by fewer than 40% of the drivers were STRAIGHT OR LEFT, LARGE ARROW, CHEVRON ALIGNMENT, ADDED LANE, LANE REDUCTION TRANSITION, DOUBLE ARROW, BUS STATION, WINTER RECREATION, SHELTER, and AMPHITHEATER. Confusion was common in the cases of certain types of signs. The most obvious were TURN/CURVE/WINDING ROAD, NATIONAL NETWORK/NATIONAL NETWORK PROHIBITED, DIVIDED HIGHWAY BEGINS/ENDS.

Results

The results of this part of the study confirm and extend the findings of other researchers who have reported lower levels of comprehension of traffic sign symbols among older drivers. Symbols which are seen on a regular basis on the roadway, and with which drivers are familiar, such as those on many of the regulatory and warning signs, are generally well understood. However, it is evident that many symbols on today's highways are poorly understood, especially by older drivers. Results of this study, including types of errors made and comments from participants, help to identify possible improvements that could be incorporated into redesign of existing symbols and the development of new ones. These findings also suggest the need for a public education campaign to inform drivers, especially older ones, of the meanings of poorly understood symbols.

Phase II

The objective of Phase II of this part of the study was to examine the level of understanding of modified and redesigned versions of 13 of the standard symbols tested in Phase I, as well as the understanding of five novel symbol messages among drivers of different ages. The selection of signs for modification and redesign was based on results of Phase I comprehension and legibility distance studies, as well as on focus group discussions and input from the project researchers and graphic design consultants.

Two hundred and nineteen volunteer licensed drivers, aged 18 and older, in Texas, Idaho, and Alberta were recruited in the same manner as for Phase I. The breakdown by age, gender, and location was essentially the same as in Phase I, and the driving background of the participants of both phases was very similar. The stimuli were 19 color slides of traffic sign symbols. Of the 19 signs tested, 7 were "Modified" and 7 were "Redesigned" versions of signs used in Phase I; another 5 were "Novel" signs. The testing procedure was the same as that used in Phase I. Subjects viewed each slide and were asked to write the meaning of each.

Results

Comprehension was poorer for the drivers 60 and older than for the younger drivers on two modified, six redesigned, and three novel symbols. As was the case in Phase I, older drivers understood traffic sign symbols more poorly than did younger ones. With the exception of one sign (RIGHT CURVE) the mean level of understanding of drivers 70 and older was below that of all other age groups, although this was not examined statistically.

Comprehension of the new designs is high for those messages that were well understood in Phase I and remained poor for those not previously well understood. Improvements in comprehension were achieved for three of the redesigned symbols but comprehension was reduced for two modified and one designed. The Novel symbols, which had never been seen before, were understood nearly as well (76% correct) as were the Modified (80.9%) and slightly better than the Redesigned (74.2%) symbols, supporting the design approach used here.

These comparisons suggest that improvements in understanding can be accomplished through redesign, and to a lesser degree through modification, especially for those standard symbol designs that are poorly understood. Of those showing significant improvement, two were categorized as poor and one as intermediate on the basis of Phase 1 results. This suggests that it may be easier to improve on the understandability of those symbols that are understood less well initially by drivers.

Conclusions