Safety Concerns

    Safety concerns have intensified over the years because the driving environment has changed with more aging drivers, altered headlamp performance and diverse vehicle sizes.

    Nighttime fatalities are over-represented

    The FHWA reports that although about one-quarter of all travel occurs at night, one-half of all fatalities occur during those hours. "It is well known that darkness reduces the visual cues available to the driver and that traffic control devices are harder to see at night."(2)
    • About 42,000 adults and children are killed on U.S. roads each year.(4)
    Rural roads are the most dangerous roads in the nations, accounting for about 60% of all fatal crashes.(5)
    • Less than one-third (28%) of all vehicle mile travel occurs on rural, non-interstate roads, yet more than one-half (52%) of all fatalities occur there(6)
    • For every 100 vehicle miles traveled, fatalities are 2.75 times higher on rural roads than on other roads(6)

    The driving population is changing

    U.S. Census Bureau reports that by 2020 more than 50 million drivers will be over 65 years old—about one in five drivers. Nearly half of these will be over 75. Aging produces a natural decline in sensory, cognitive and motor (physical) functioning(7):
    • Reduced eyesight (visual acuity) and increased glare sensitivity
    • Reduced hearing, flexibility and mobility
    • Slower (longer) reaction times
    The FHWA has determined that easier-to-see-and-read signs can help old drivers retain their freedom of mobility, remain independent and reduce their likelihood of being involved in traffic crashes.(2)

    Headlamp performance has changed

    An FHWA-sponsored literature review and field study noted several motor vehicle models did not provide sufficient illumination toward mounted signs.(8) Currently about 80% of late model vehicles are factory-equipped with VOA (visually/optically aimed) headlamps that compromise sign performance.(9)
    • 53% lower visibility on the right shoulder
    • 42% lower visibility on the left shoulder
    • 28% lower visibility overhead

    Drivers of large vehicles are disadvantaged(10)

    Over the last decade, the number of registered passenger cars has remained unchanged while the number of trucks on U.S. roads has increased 60%. Passenger cars generally have headlamp and seating positions that result in smaller observation angles compared to pickups and SUVs. Large trucks routinely account for nearly 40 percent of the traffic mix on interstate highways at certain times of the day.(11)

    Studies(11) conclude that more emphasis should be placed on observation angles than entrance angles because every motorist will experience a 0.2, 0.5, 1.0, 1.5 and possibly a 2.0-degree observation angle (which is considered "wide angle"). These angles get larger every second as we drive toward a retroreflective sign. If the vehicle is a tractor-trailer, the driver could experience a 3-degree observation angle.

    2 Night Lights…lighting the way (Answering Your Questions about Traffic Sign Retroreflectivity), U.S. Department of Transportation, Federal Highway Administration
    4 Traffic Safety Facts, 2005, NHSTA National Center for Statistics and Analysis, Fatality Analysis Reporting System (FARS)
    5 Peaslee, G., Signs show the way to cost-effective rural safety, Public Roads, January/February 2005
    6 http://www.merginet.com/index.cfm?searched=/clinical/trauma/rural_traffic.cfm
    7 Schieber, Driver eye fixation and reading patterns while using highway signs under dynamic driving conditions…, TRB 2004 Annual Meeting CD-ROM
    8 Russell, E.R., et al, Characteristics and needs for overhead guide sign illumination from vehicular headlamps, FHWA-D-98-135
    9 Sivak, M, et al, A first look at visually aimable and harmonized low-beam headlamps, UMTRI-2000-1
    10 Carlson, P. et al, Developing updated minimum in-service retroreflectivity values for traffic signs, TRB Paper 03-2377
    11 Brich, S., What is an appropriate sign sheeting specification for prismatic construction and maintenance signs?, Virginia DOT
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