From Tech Transfer Newsletter, Fall 1999 » printer-friendly

Genesis of an Innovation: Pavement Markers Reflect the History of an Idea

Raised reflective pavement markers capture light from oncoming headlights and reflect this light back to drivers for guidance at night and in weather with poor visibility. They are a familiar feature on many California freeways. Their origins can be traced to the ingenuity of British civilians trying to cope with the imposition of blackouts during bombing raids in World War II. Night drivers were required to shield the top of their headlights with blinders. This drastically cut down on the night drivers' vision on the roadways. Someone came up with the idea of placing reflective markers on the roadways which would be visible only to drivers. These were soon nicknamed "cats' eyes" because of how they appeared to drivers on the darkened roadways."

The high cost of paint initially encouraged the use of raised markers in California. Line painting crews need to repaint lines as much as three times a year to keep highways well maintained. Besides the cost of labor and paint, there is the constant aggravation to drivers who must maneuver around road closures. "Bott's Dots" were the first solution to this problem. In 1953 Dr. Elbert D. Botts, a traffic engineer at the Caltrans materials testing lab in Sacramento, developed a raised pavement marker to help make the painted lines separating lanes last longer. His dots were made of ceramic and glued onto roadways with epoxy. They were more permanent than the painted lines, and because they were raised they provided the additional safety feature of warning motorists when they strayed from their lane. After some refinements, Botts' Dots were mandated for all California freeways, except in areas where they would be damaged in snow-removal operations. But Bott's Dots were not particularly visible at night. In 1960, Caltrans asked the Stimsonite company for help solving this problem. Stimsonite, headquartered in New Jersey, was known as an innovator in reflective products used in other highway safety applications. In late 1963, after almost four years of research and development, the first reflective version of the Bott's raised pavement markers were installed on the Golden Gate Bridge. Today there are an estimated 20 million dots on California freeways and highways — a lasting legacy to Mr. Botts, who passed away in 1962.

Use of the raised reflective pavement markers spread quickly from California to Florida and Texas, and then throughout the country and the world. But as this occurred a new variable arose. The markers needed to be durable and functional in a variety of weather conditions, from desert heat to mountain snow. Stimsonite was soon back at the drawing boards, focused on making the markers able to withstand the snowplow. The product they developed was the Life-Lite which first appeared in 1977 as a snowplowable marker with an iron casing installed in Pennsylvania and New Jersey. Raised reflective markers guide drivers from as far away as 1000 feet down the road, in all weather conditions, providing feedback which is especially important in typically hazardous zones including: exit ramps; bridge approaches; lane transitions; horizontal curves; and construction zones. In some states, markers are placed on all roads with high traffic volumes, such as interstates, urban expressways, and multilane highways. Major secondary roads, usually the main urban and rural routes in cities and counties are usually the final roads targeted for marker installation. Today a new emphasis on safety at the state and federal level has spawned a renewed interest in markers. Many state and local officials are eager to add safety features to roadways, even on less traveled roads, particularly as speed limits are increased.

To install markers, pavement cuts are made and the markers are sealed into place with epoxy. When installed, the markers protrude approximately 1/4 inch from the level surface. White and yellow reflective markers are generally used to mimic painted lines. Red reflective markers are used as WRONG WAY indicators. These conventions are described in the 1983 "Traffic Control Devices Handbook" issued by the Federal Highway Administration. In the early 1980's mini-truck owners in the Western states began lowering their trucks to the point where the U-bolts holdingthe springs to the axles would strike markers and rip them from the road surface. The U.S. Department of Transportation, beleaguered by the cost of constantly replacing the "Bott's Dots", just recently announced that it was unveiling a new marker that should prove to be a deterrent to the illegally lowered mini-trucks,

Although some engineers believe that every paved road would be safer with raised reflective markers, not everyone is completely happy about that idea. Some cyclists for example view the dots as hazardous at turns. It is likely that one more round of innovation is about to begin. But when an innovative spirit reigns, improvement is never far away. In this process everyone plays a role; citizens, government and private industry.

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