On the Button : The Quest to Perfect Botts’ Dots Continues

In the era of “smart highways,” in which computerized cars and roadbed sensors can help a driver avoid accidents, detect congestion ahead and map out the fastest route home, they might seem like little more than anachronistic bumps in the road.

But when it comes to keeping cars on the straight and narrow, Botts’ Dots have accomplished far more for less money than any number of electronic gizmos under development.

Named for Elbert D. Botts, a senior state chemical testing engineer who died in 1962, the raised pavement markers that jostle sleepy drivers awake and help everyone find their lanes in the rain have preempted countless accidents and given the Golden State another “first” that is sweeping the world.

Not that anyone would guess this from the festivities marking their 25th anniversary of use. There aren’t any planned.

But events leading up to the day a quarter-century ago when legislators mandated the little lumps for all snow-free highways illustrate not only California’s attention to freeways but also its willingness to subsidize car travel in ways not apparent to the drivers who benefit.

Considering that 17,067,400 dots had been plopped on the pavement by 1989, the date of the most recent census, there are more Botts’ Dots in California than there are autos to run over them, and about 4,100 more are pasted in place each day. Even as the utilitarian saucers make an impression on millions of drivers, the scientific quest for a perfect dot proceeds unabated.

“Research continues” at Caltrans, said Earl Shirley, chief of the new technology division of the state transportation department materials and research laboratory in Sacramento, “and, in the private sector, people always come up with new ideas that they want us to check out.”

New designs are now torture-tested on California 99 south of Sacramento, where lots of trucks make lots of lane changes. Any design that survives that extraordinary pounding is eligible for a place on the state’s highways--and on the lane-marker history board, a kind of Dot Hall of Fame, that takes up a wall in the Caltrans lab.

“We have every kind we’ve ever used up there,” Shirley said. “There are little ones and big ones; cement ones and metal ones. All types.”

Right now, said Russ Snyder of the Caltrans district in Los Angeles, where 3.2 million dots reside, “there are all kinds of these little jobbers” approved for California’s freeways. Actually, there are five approved models--plain, round “button dots” in white or yellow, and reflective square “wedges” in white, yellow, and red and white.

Reflectors are mostly plastic. Buttons, the most common variety, are made of clay, plastic or polyester, and can hang onto a highway for as long as six years. Pounding truck traffic in Los Angeles has been known to dislodge some in as little as six months.

“It depends on a lot of things,” said Caltrans spokeswoman Mariana Mejia, “including the amount of traffic, the amount of truck traffic and the amount of lane changes.”

In some spots, Mejia noted, Botts’ Dots have outlasted the road underneath them. She said that in deserts, especially, “the dots are often harder and more durable than the pavement.”

Mejia said the plain dots cost about 40 cents each, while the fancy reflectorized ones run about a buck apiece. Shirley added that despite popular and persistent rumors to the contrary, they are not patented. The only people to make money off them are manufacturers--more than a dozen in the United States, Mexico and Taiwan.

Each vies to satisfy California’s appetite for about 1.5 million dots a year, Mejia said. With so many to choose from, Caltrans samples each lot of 25,000--testing for color, reflectivity, bondability and, most important, the ability to resist cracking.

California is particularly finicky because it is where Botts’ Dots were born.

Caltrans, when it was still the Division of Highways, toyed with the idea of raised markers as early as 1936. But the notion did not gain any urgency until 1953, when traffic volumes and speeds began to climb on the new freeways.

Development of durable epoxy resins also speeded development of markers by letting engineers attach bumps to roads without using spikes, a potentially tire-flattening alternative should the bump break and expose the metal.

At first, engineers toyed with the idea of depositing epoxy lumps on highways, but that was rejected as too expensive and difficult. Instead, they opted to experiment with using the new glue to bond markers to roads.

But markers made of what? Cast epoxy resin was an obvious candidate, but several other materials also had supporters--from relatively cheap Portland cement to more exotic polyester filled with reflective glass beads. Some scientists advocated a simple button shape, while others lobbied for a streamlined wedge.

In the spring of 1955, a team of state highway engineers left their laboratory and ventured onto a new freeway in western Sacramento to test their theories.

The researchers experimented with adhesives, including a tape, before concluding that epoxy worked best. They studied the reflectivity of titanium dioxide paint and glass beads. They analyzed the effectiveness of different shapes. When some markers broke off, the researchers went back to the lab and explained why by comparing the “coefficient of thermal expansion” of dot ingredients.

Botts oversaw research in the Division of Highways’ chemical laboratory during this period, but no one bothered to document what he contributed to the birth of the modern raised pavement marker versus what was contributed by those who worked under him.

When Botts died in April, 1962, two years after he had retired, a one-paragraph obituary in the Materials and Research Department newsletter, “Random Samples,” did not even mention his pioneering work in dots.

The research he oversaw was tabulated, filed and--for a time--forgotten.

State engineers came back to the idea of a raised pavement marker in 1964. In the spirit of an era when state budgets were booming and cars were king, they devised a more complicated dot with a shortened life span.

Their new and improved dot--described in a 1968 Division of Highways research report as an “aluminized acrylic cube corner unit encased in an acrylic plastic shell with the interior of the marker being a filled epoxy resin system”--shone “brilliantly” at night but hardly at all during the day. Instead of lasting five to 10 years, as did dots of an earlier era, these high-tech wonders had a life span of three to five years.

When the time came to road-test the dot again, on Interstate 80 near Vacaville in 1965, the Division of Highways decided to use clusters of four old-fashioned polyester or epoxy button dots interspersed with individual new reflectors.

The combination--still used today--worked well enough to foster thoughts of doing away with the dangerous and expensive task of painting stripes on the road.

Early installations along highways around the state in the spring of 1966 showed that tires were scuffing up the polyester and epoxy markers, turning them from white to black and thereby considerably reducing their effectiveness. The lab boys, led by engineer Herbert A. Rooney, swung into action.

They noted that the scuffs, which they identified as hot carbon deposits, could be scrubbed off easily enough, but scrubbing dirty dots on a busy freeway seemed a dicey job at best. They turned their attention to scuff-resistant ceramic markers being tried elsewhere.

Any concerns that the brittle ceramic markers could not stand up to traffic crumbled after a bunch were tested in a busy crosswalk. Despite a full year of “high traffic density, extreme acceleration and deceleration, and damage from gravel dropped from trucks,” a report marveled that the ceramic dots not only resisted scuffing, they resisted wear as well.

Ceramic dots used today are expected to last about six years.

In 1965, though, engineers were skeptical. To see whether a ceramic dot would indeed resist scuffing at freeway speeds, engineers at first returned to the laboratory. They tried pressing test dots against a rotating tire. Scuffing was observed. They then put a test dot--heated to 150 degrees Fahrenheit with heat lamps--in the path of a truck tire rotating in a circle seven feet in diameter. Scuffing was again noted.

What the scientists evidently forgot was that some ceramic markers were already in service. After all the tests were done, they noticed that freeway experience showed scuffing was minimal. The test results were ignored.

That opened the way for the Legislature, in September, 1966, to require the installation of raised pavement markers on all California freeways--snow-free freeways, that is. Plows plying roads in the Sierra Nevada tend to scrape up dots as well as snow.

“At that time, (dots) were a real advancement,” said Caltrans’ Earl Shirley. “They stuck above the road surface, so they gave us good visibility. That was especially important when it rained because when a sheet of water spreads across a road and light reflects off of it, you just can’t see a painted stripe.”

Even after Botts’ Dots were put into wide use, research forged bravely ahead--and continues to this day.

While the National Aeronautics and Space Administration raced for the moon in the summer of 1967, California highway engineers scrambled for a better marker, dabbling with such space-age materials as acrylonitrile butadiene styrene, alkyd, melamine--even Pyroceram, the miracle stuff of rocket nose cones. Each in its turn was nominated, studied and rejected.

When it was observed that a speeding vehicle could crack brittle ceramic markers on pliable asphalt, researchers responded by putting the dots on butyl pads an eighth of an inch thick--and cracking virtually vanished.

Meanwhile, reflective lane markers also were re-engineered. Shapes were changed to maximize the polishing effect of tires racing over them, reflective surfaces enlarged to improve “light return” factor, cases hardened to extend their life, and rear reflectors made red to warn wrong-way drivers.

Other scientists tackled the snow-plow issue. At first, they recommended recessing standard ceramic markers in the road surface. While sunken buttons worked better than a painted stripe, the R & D boys had to concede in reports that “their effectiveness as lane delineators has been rather poor.” Wedge-shaped steel buttons didn’t work. Finally, they settled on using recessed reflectors on mountain roads.

Epoxy, which made the modern dots practical, was supplanted three or four years ago by a superheated asphalt-based adhesive that is cheaper and more flexible, Shirley said.

Then, research indicated that the spacing between dots could be increased without appreciably reducing their effectiveness, which significantly reduced the number that need to be installed and replaced. Last year, Caltrans spent $3.8 million replacing or repairing 864,000 dots around the state.

Earlier this year, Caltrans researchers unveiled a new way to place the dots on the road--an automated truck that squirts a precisely measured wad of adhesive on the road, then deposits and tamps down a Botts’ Dot with exactly the right pressure.

The truck, developed with the help of students from UC Davis and Cal State Sacramento, is not only safer, relieving workers of the need to stand in traffic and handle 420-degree asphalt adhesive, it also ensures standardized dot placement and consistent quality.

In short, Caltrans crows, a longer-lasting Botts’ Dot.

Even at that, science marches on. Caltrans researchers are already back in their workshops, laboring to increase the number of Botts’ Dots, now 216, the trucks can apply between refills. Before they build more trucks, technicians also are trying to speed up the mechanism that puts dots on the road so the truck will not have to continually stop and start.

And, of course, the people in the white lab coats continue to dream of the ultimate dot.

“Chemistry and materials sciences are evolving all the time,” Shirley said, “and as long as that goes on, my guess is that we’ll continue to look for something that is cheaper, better and more durable.”

Lots of Dots By 1989, the date of the most recent count, there were 17, 067,400 Bott’s Dots on California highways, meaning there are more dots in the state than autos to run over them. That is enough dots to: * Form an unbroken line 1,000 miles long on coastal highways from Mexico to Oregon. * Stack high enough to interfere with space shuttles zooming 184 miles above the Earth. * Maintaining that many dots is itself a monumental and costly chore. Caltrans crews last year replaced or repaired 864,000 dots around the state at a cost of $3.8 million-almost $4.40 per dot.Source: California Department of Transportation, Los Angeles Times