Bright and shining moment

Roads & Bridges / January 22, 2008

Motorists nationwide should begin seeing improved traffic signing within the next year as new standards for highway sign performance are adopted. The new guidelines were expected to be published by the Federal Highway Administration (FHWA) in December.

The time has come

The new minimum reflectivity standards will specify the level of reflectivity a sign must retain. The minimum requirements vary based on the various standard sign classifications. As part of the process, agencies will be required to have an inventory documenting what types of signs they have in which locations and the measured or expected reflectivity level of each sign. Expected reflectivity levels are based on factors such as a sign’s age and the type of reflective material from which it is fabricated.

The FHWA itself refers to traffic signs as “the principal medium by which highway agencies communicate information to road users. It’s crucial that they be detectable, legible and comprehensible to users.” Signs are designed to satisfy these requirements by selection of size, color, style, size of letters and symbols and the retroreflective material they are fabricated from. Through appropriate selection of these various design parameters, signs must meet drivers’ needs under both day and night conditions.

Safety advocates and industry groups have been promoting minimum sign performance standards for years, arguing that better highway signage makes roads safer for all drivers, particularly older ones who require more light to effectively see at night.

“It’s about time,” said Roger Wentz, executive director of the American Traffic Safety Services Association (ATSSA). “This originally was approved by Congress in the 1992 Transportation Appropriations Act. It’s taken 15 years to become reality, but finally every sign in the country will eventually meet some minimum level of brightness for motorists.”

Another 200 ft

Indeed, in 1992 Congress directed the secretary of transportation to revise the Manual on Uniform Traffic Control Devices (MUTCD) to include “a standard of minimum levels of retroreflectivity that must be maintained for traffic signs.” But despite almost continuous debate since then, no firm standards have been incorporated into the manual.

Since its introduction in 1935, every version of the MUTCD has included requirements for nighttime sign visibility. Over that time, a variety of sign materials have evolved that provide options to meet detectability and legibility objectives, but there have been no specific design or maintenance thresholds.

“From a human factors and visibility standpoint, I’m always looking for an extra 150 to 200 ft of distance,” said Dr. Ronald Gibbons of the Lighting and Infrastructure Technology group at the Virginia Tech Transportation Institute. “There’s a relationship between brighter signs and farther visibility distances. The farther a person is away from an object when they see, recognize or read it, the more distance they have to react and execute whatever maneuver they need to make.”

The rigors of different climates and changing weather conditions cause signs to naturally and slowly deteriorate over time. As colors fade, contrast between the sign’s legend and its background is reduced. The loss of these distinguishing features makes older signs less detectable and legible, even under daylight conditions. The new minimum performance standards are intended to prevent signs from reaching this condition, always assuring an adequate level of legibility and reflectivity to safely guide motorists.

Change is of European descent

While the total number of U.S. traffic fatalities has fallen over the past several decades, the percentage of accidents that occur at night is still disproportionately high. “We know that 50% of all fatalities occur at night, even though nighttime accounts for only 25% of total traffic volume,” said Greg Cohen, president and CEO of the American Highway Users Alliance.

Cohen’s group joined AAA and AARP in encouraging adoption of the new guidelines. In a joint communiqué to the U.S. Department of Transportation, the motorist advocacy groups urged that “minimum maintained retroreflectivity levels” be adopted by the FHWA and incorporated into the MUTCD. The groups point toward statistics that show there were 571 more nighttime fatalities in 2005 than in the previous year. The groups concluded that “signs maintained at a sufficient level of brightness will contribute significantly to safer driving for all motorists.”

The initiative for the new standards was influenced by more than older driver needs. The adoption of traditional European headlamp technology (also known as visually optically aimable, or VOA) has had a significant influence on sign performance. The lamps have a distinct horizontal cutoff to reduce glare for oncoming motorists. But a negative result of the design is that much less headlight illumination hits signs, reducing the amount of light that can be reflected back to the driver.

“A more efficient sign sheeting is a benefit because it can return a greater percentage of a smaller amount of light,” said Gibbons.

Advances in optics technology now allow for sign materials that are 10 times brighter than earlier generations and reflect a far greater percentage of the light that hits them. Newer materials are more durable and more angular in performance and carry longer warranties.

Less changing

Concerns have been voiced over the potential cost of the new standards, since higher-performance reflective sheetings will be needed to meet the higher brightness requirements. But the FHWA points out that when analyzed from a life-cycle perspective, the changes should result in long-term savings for agencies. While higher-performance reflective materials cost more, they also carry proportionately longer warranties and service lives. And because reflective material is such a small percentage of the overall sign cost, the FHWA estimates that higher-performance reflective material will add less than $7 to the total cost of an average 36-in. x 36-in. sign. Signs that used to need replacing as frequently as every seven years can last as long as 15 years with more durable, high-performance sheetings. Over a longer span of time, say 30 years, signs that used to need replacing four times now may only need to be replaced twice. The average annual savings over the life cycle of the sign is significant.

It may be as long as a decade before all signs covered under the new guidelines are updated, because agencies will have the leeway to transition to the new standards over a period of time. It is expected that most agencies will upgrade signs during normal sign maintenance or replacement cycles. Some categories of signs deemed “noncritical,” such as No Parking signs, will be excluded from the new standards.

The FHWA concluded that “night visibility of traffic control devices is critical to the safe and efficient operation of roadways at night . . . and represents one area where immediate night visibility improvements are possible to enhance the delineation of the roadway, warn drivers of unexpected conditions and facilitate their abilities to navigate the road system.”

More information, including all the technical details of the minimum reflectivity ruling, can be obtained at www.minimumreflectivity.org.

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