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Traffic Signs Performance Factors
Traffic Signs Performance FactorsDespite improvements in traffic safety over the past decade, several current trends reduce the ability of traffic signs to provide guidance and safety – making signs that return more light to drivers are more important than ever.
Traffic Signs Performance FactorsDespite improvements in traffic safety over the past decade, several current trends reduce the ability of traffic signs to provide guidance and safety – making signs that return more light to drivers are more important than ever.
Traffic Signs Performance FactorsDespite improvements in traffic safety over the past decade, several current trends reduce the ability of traffic signs to provide guidance and safety – making signs that return more light to drivers are more important than ever.
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Older Drivers
In the U.S., nearly 8,000 baby boomers turn 65 every day—a trend that is expected to continue well into the future. By 2020, the U.S. population will include nearly 56 million citizens age 65 and older, and by 2030 that numbers swells to more than 72 million. In addition, older adults are keeping their driver licenses longer. In 2010, 80 percent of the 70-and-older population was licensed to drive—approximately 22.3 million seniors—and this number will continue to rise.¹ As people age, there is a decline in many of the abilities considered necessary to safely operate a motor vehicle. Older people, as a group, have reduced visual acuity, narrower visual fields, poorer nighttime vision, greater sensitivity to glare, slower reaction times, more attention deficits, reduced muscle strength, reduced flexibility and range of motion, and other declines in visual, cognitive, and psychomotor function that can adversely affect driving.² Prolonging the mobility and independence of older adults is an important social goal. Improving the visibility of road signs and pavement markings can be particularly important for older drivers who—between the ages of 60 and 80—need three to six times more light to see than a 20-year-old.³ Maintained sign retroflectivity, larger signs with increased letter height, advance warning and street signs, improved road delineation with wider, well-maintained pavement markings and more traffic control in work zones are some of the recommended low cost safety improvements that can benefit older drivers.
¹Insurance Institute for Highway Safety, iihs.org/research/qanda/older_people.aspx
²National Cooperative Highway Research Program, NCHRP Report 500
³American Automobile Association, Inc., SeniorDriving.AAA.com
Trends Affecting Sign PerformanceHeadlight Design
Low Cut-off Headlights
Since the late 1990s, vehicle manufacturers have transitioned to new headlight designs like Visually Optically Aimable (VOA) or low cut-off headlights. Designed as a solution to reduce the amount of glare drivers experience from oncoming traffic, these headlights have a sharp, horizontal cut-off and emit little light above the headlight level. Low-cut off headlights have a profound effect on a vehicle’s ability to illuminate road signs. The most recent headlight models in the U.S. do not provide as much illumination as did an average vehicle in 1997 for the most commonly viewed signs (on the right shoulder) at distances associated with typical sign reading. For a typical right-shoulder mounted sign in the U.S., viewed at distances between 300 feet and 900 feet, the reduction in illumination from 1997 to 2011 model headlights was anywhere from 24 percent up to 48 percent. ¹ With newer generation VOA headlights sold in 2004 through 2011 model vehicles, some disadvantaged locations (left shoulder and overhead signs) showed slight improvement in illumation.¹ However, considering that a left shoulder mounted sign receives around 20 percent, and an overhead sign receives around 10 percent, of the illumination received by the right shoulder mounted sign, these signs are still very disadvantaged in terms of headlight illumination.
¹Flannagan, M.J., and Schoettle, B., An Analysis of Low-Beam and High-Beam Headlighting Performance in the U.S.: 1997-2011, University of Michigan Transportation Research Institute, 2012. Contact 3M for the full report.
Diverse Vehicle Sizes
Larger Vehicles, Different Observation Angles
Vehicle size makes a difference in a driver’s ability to see traffic signs at night. The same sign may appear less bright to drivers of SUV s and large trucks than it does to drivers of passenger vehicles.
The number of large trucks registered in the U.S. has increased steadily over the last two decades, reaching almost 11 million in 2009. During that same time, truck traffic (as a percent of vehicle miles traveled) has doubled, nearing 300 billion miles in the U.S. in 2009.¹ The FHWA reports that by 2040, long-haul freight truck traffic in the U.S. is expected to increase dramatically on the National Highway System and may reach 590 million miles per day.² And, unlike automobile and business-truck traffic that peaks between the daytime hours of 7:00 a.m. and 7:00 p.m., long-haul truck traffic has a flat time-of-day distribution, with as many vehicles traveling during nighttime hours as during the day.³
When it comes to seeing traffic signs at night, drivers of large vehicles are at a particular disadvantage because of their observation angle (the measure of separation between a driver’s eyes and his or her headlights) is significantly greater. See Understanding Angularity for more information.
How important is this measure? Large trucks can have twice the observation angle of passenger vehicles at the same distance. That means there’s much less reflected light available for these drivers to see road signs. Drivers of large vehicles can greatly benefit from signs made with high performance reflective sheeting that returns more light in a larger cone of reflectivity.
¹Commercial Motor Vehicle Facts - November 2011, U.S. Department of Transportation
²FHWA-HOP-13-001 - Freight Facts and Figures, 2012
³ FHWA-RD-98-117 - Understanding Traffic Variations by Vehicle Classifications
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