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Auto and Road User Journal
Copyright © 1997 by TranSafety, Inc.
February 1, 1997
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Highway Safety Publications Catalog. Articles on Road Engineering, Road Maintenance & Management, and Injury Litigation. Information and consulting for the Automobile and Road User, as well as for law professionals in accident investigations.
TranSafety's free consumer journal for automobile and road users, three subscription journals on road maintenance, engineering, and injury litigation, and highway safety publications catalog. See our free consumer journal for automobile and road users, three subscription journals on road maintenance, engineering, and injury litigation, and a highway safety publications catalog.

Improving Highways for Older Driver Use

The number of people over 75 years of age will double by the year 2000, and people over 65 will make up 20 percent of the United States population by 2020. Statistics show that senior drivers have a high rate of accidents, injuries, and fatalities for each mile they drive; however, the ability of older people to maintain an independent lifestyle often depends on continuing to drive. Therefore, the Federal Highway Administration (FHWA) considers research related to designing roadways that are safer and more usable for seniors a top priority.

Elizabeth Alicandri presented her paper, "Highways Older Drivers Can Use," in Hershey, Pennsylvania at the May 1994 American Society of Civil Engineers' conference entitled "Innovations in Highway Safety--A Broad Perspective." The paper summarized results of FHWA's ongoing efforts to identify and evaluate improvements in roadway design that will help older drivers. FHWA calls their program, which began in 1989, "Improved Highway Travel for an Aging Population."

Ms. Alicandri divided her report on FHWA research into four categories: traffic control devices, geometric design, intelligent vehicle-highway systems, and future efforts.

Traffic Control Devices
The Manual on Uniform Traffic Control Devices (U.S. Department of Transportation, 1988) states that traffic control devices (TCDs) function "to direct and assist vehicle operators in the guidance and navigation tasks required to traverse safely any facility open to public travel." The research described in this article concerned four types of TCDs: highway signs, traffic signals, delineation (painted stripes, raised pavement markers, and post-mounted delineators), and object markers.

Traffic Signs: One cause of accidents involving senior drivers is failure to heed traffic signs. Four characteristics of older drivers may contribute: reduced visual acuity, lessened cognitive ability to take in and process information, increased difficulty with dividing attention among tasks, and lack of familiarity with today's highway signs and markings. To serve the needs of older drivers, traffic signs must be sufficiently conspicuous, legible, and understandable to overcome the psychomotor, perceptual, and cognitive deteriorations that occur with aging.

Efforts to address these problems have focused on making traffic signs bigger and brighter. A 1990 study showed that for older drivers to read signs as well as their younger counterparts, they may need sign letters to be 30 percent larger. Since a one-third increase in letter size may require a 60 to 80 percent increase in sign size, making letters bigger becomes an expensive solution. A 1994 study showed that younger drivers could read traffic signs farther away in daylight than in darkness (600 feet in daylight and 300 feet at night). Older drivers, however, needed as much distance to read a sign during the day as they did at night. Experiments with taller lettering on traffic signs showed that making letters more than 16 inches high brought diminishing results. Therefore, FHWA is studying other ways to revise traffic signs for older drivers.

Research suggested that redundant signing sometimes improved accuracy and speed of decision making for older drivers confronted by protected left-turn intersections or changeable-message signs. The authors cautioned that visual clutter is, however, also a problem for older drivers. Consequently, highway designers must balance the benefits of redundant signing against the creation of too much background clutter.

Design engineers often use percentiles as cut-off standards for engineering legible traffic signs. However, studies showed that regulatory and construction signs that met legibility requirements for younger drivers safely satisfied the needs of only 85 percent of older drivers. Guide signs meeting the requirements of younger drivers met the needs of only 50 percent of older drivers. Further analysis "showed that larger signs with engineering grade materials are generally more cost effective/efficient that smaller signs with diamond grade sheeting for initial implementation." The authors recommended more research in these areas.

Another FHWA study addressed the benefits of using symbol signs rather than text signs--a practice that has been increasing in popularity since the 1970s. Of the 85 signs investigated, only 28 were understood by more than 90 percent of respondents, and 10 signs were understood by only 10 percent of respondents. In addition, younger drivers showed a better understanding of 39 percent of the symbol signs than did older drivers. As with text signs, older drivers showed longer recognition distances for symbol signs than their young and middle-aged counterparts. Moreover, recognition distances for older drivers varied significantly from sign to sign and from daytime to darkness. Finally, research tested "glance legibility" for a set of 18 symbol signs--6 with good ratings for comprehension and recognition distance, 6 with intermediate ratings, and 6 with poor ratings. Older drivers showed longer glance legibility times overall, and the results showed the greatest differences for the poorly rated signs.

A second phase of symbol sign studies used 7 modified, 6 redesigned, and 5 novel signs. Modification and redesign efforts focused on removing fine detail and increasing the space between symbol elements. This resulted in simpler, bolder symbol signs. More drivers, young and old, understood the modified and redesigned signs, and all drivers could recognize them from greater distances.

Traffic Signals: Since roadway standards allow considerable latitude in signal design and placement, all traffic signals do not look alike nor are they at the same place in different intersections. Older drivers react more slowly to novelty than their younger counterparts; therefore, this lack of consistency may create a hazard for senior motorists.

Delineation: The authors described delineators as "painted stripes on the road, raised pavement markers (RPMs), and post[-]mounted delineators used to define lanes, road edges and other geometric features of the highway system." After studying 24 enhanced delineation methods, FHWA is concentrating on 11 new treatments. Delineation improvements included widely spaced raised pavement markers (twice as far apart as the current standard) and a new design for post-mounted delineators. Enhanced roadway delineators will help older motorists, especially in difficult nighttime driving situations.

Object Markers: Research showed that all drivers had difficulty with object markers that identify hazards on or near the roadway. Studies focusing on the most effective size, shape, and color for markers showed that research participants noticed only 39 percent of the object markers they viewed in slide-based test situations. Best understood were Type 3 markers (1-by-3-foot vertical rectangles with black and yellow 45-degree stripes) followed by Type 2 markers (small yellow or white rectangles with yellow reflectorized buttons). Least effective were Type 1 markers (18-inch yellow diamonds or yellow or black diamonds with reflectorized yellow buttons). Preferences varied according to the age of drivers. Older drivers preferred diamonds or circles that depicted the actual hazard on a white background, and younger drivers preferred square signs with abstract symbols and green or yellow-green backgrounds. The authors did not mention color preferences for the symbols.

Geometric Design
Standards for roadway geometric designs depend on such human factor requirements as intersection sight distance, stopping sight distance, and decision sight distance. While all sight-distance requirements appeared to increase with age, American Association of Highway and Transportation Officials' (AASHTO's) standards providing 2 seconds of perception-reaction time for intersection sight distance seemed adequate for drivers of all ages. Researchers also observed that younger drivers showed shorter average perception-reaction times for stopping sight distance than older drivers; however, AASHTO's design value of 2.5 seconds stopping sight distance also proved adequate here for all drivers. Older drivers compensate for increased perception-reaction times by such strategies as reducing driving speeds and eliminating distractions within their vehicles.

Older drivers had slower perception-reaction times than younger drivers in situations requiring them to make complex decisions or execute unexpected maneuvers. Researchers found that overall perception-reaction times in such situations for drivers 20 to 40 years old were 3.6 seconds compared with 4.5 seconds for 65 to 69 year olds and 5.5 seconds for drivers 70 and over. However, of the older drivers who talked with researchers in focus groups, only 28 percent said they thought their reaction times were slower than the "average" driver. Only 18 percent thought their reaction times had slowed over the last ten years.

FHWA is giving special attention to problems older drivers encounter on freeways when they must make such high-speed decisions as merging and changing lanes. These complex driving tasks require an ability to attend to visual input from more than one direction and make accurate, quick decisions. Since these abilities deteriorate with age, older drivers require more time to make safe merging and lane-changing decisions on high-speed roadways.

Intersections present another instance where driving requires quick and accurate decision making and complex maneuvering in response to numerous stimuli. Statistics show that seniors are over-represented in intersection accidents. Interviews with older drivers revealed problems with skewed intersections, particularly where intersection angles of more or less than 90 degrees created a design that required tight left turns. Older drivers expressed a preference "for turn lanes separated by some type of physical barrier from other traffic and for raised or painted pavement on the left-side of a left-turn bay." To find ways to decrease accident rates at intersections for older drivers, FHWA is conducting field studies with offset left-turn lanes and increased curb radii.

Intelligent Vehicle Highway Systems (IVHS)
Government agencies and private industry are joining colleges and universities in developing Intelligent Vehicle-Highway System (IVHS) technology "to improve travel efficiency and mobility, enhance safety, conserve energy, provide economic benefits, and protect the environment." One part of IVHS, Advanced Traveler Information Systems (ATIS), focuses on providing in-vehicle information to drivers about routes, services, roadway signs, and upcoming hazards. Studies to decide whether to use flat or three-dimensional in-vehicle images had shown that speed and accuracy of response to ATIS information were better for younger drivers than for older persons. Further studies will compare the benefits of heads-up versus in-dashboard displays for younger, middle-age, and older drivers. The research had revealed that spatial skills deteriorate as drivers age. FHWA will continue to work toward finding the best applications of IVHS and ATIS for an aging driving population.

Future Efforts
FHWA is working on a highway design handbook summarizing research findings on older drivers, and they will continue to make older driver concerns a high priority in their research and design efforts. The authors mentioned that "planned efforts include investigations of construction and maintenance zones, driver perception of hazards, and development of a driver performance model which will include older driver capabilities."
The goal is to enhance both the safety and mobility of older drivers in recognition of the critical role driving plays in allowing seniors to maintain an independent lifestyle.

Copyright © 1997 by TranSafety, Inc.


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