So you're in your own lane minding your own business when a certain song comes on the radio and you just have to turn it up. Suddenly, bup bup bup -- you're driving over these little white bumps and you realize you just drifted over the line ever so slightly.
Those bumps are known as raised pavement markers, or "Botts’ Dots." In 1953, Dr. Elbert D. Botts, working in the Caltrans materials testing lab in Sacramento, came upon the idea of using a raised pavement marker to help make the painted lines separating lanes last longer. After a many refinements, the use of Botts' Dots were mandated for all California freeways, except in areas where they would be damaged in snow-removal operations. The ubiquitous little buttons have since been adopted around the world. In addition to making lanes easier to distinguish, the markers also had an additional -- and originally unintended -- safety benefit: to alert motorists when they drift out of their lane. There are an estimated 20 million Botts” Dots in place today on California freeways and highways -- a lasting legacy to Mr. Botts, who passed away in 1962.
Many things have changed since the 50's, however, and Caltrans currently is studying the cost and effectiveness of raised pavement markers and their use in varying situations around California.
No, Caltrans is not thinking about getting rid of them any time soon.
We've used other materials for markers in certain situations (plastic, ceramic, polyester), different kinds of glues (standard and rapid-set epoxies and bituminous adhesives), and different types of stripes (paint, dots, and thermoplastic stripes). And since the department has been using various markers for more than 30 years now, it seems reasonable to step back and take a look at how well they work from two angles: safety and cost.
Safety: Caltrans must consider the safety both of motorists and its workers. While the department does not have extensive data at this time, it appears other kinds of pavement markers may keep motorists about as safe and last about as long in some situations as the raised ones -- plastic stripes, placed on the pavement at high temperature, are one kind.
We also must protect our workers. Placing or replacing the markers is a one-at-a-time job, and that means that Caltrans or contract workers have to get out there and glue them down. Any time workers are near traffic, they are exposed to drunk drivers, bad drivers and bad vehicles. Anything that shortens workers' time on the roadway means greater safety.
Cost: Caltrans also has to consider whether the first-time plus lifetime cost of the various markers is justified in all situations. Both the durability of the marker and that of the material used to glue it to the pavement are factors. Some materials seem to work better in certain situations -- dry desert conditions as opposed to wet coastal ones, for example -- than others. Some seem to work better where there is more traffic, especially weaving traffic. Raised markers -- dots -- can¹t be used where there is snow, because snowplows destroy them.
We are looking to undertake a study of these issues and alternatives to determine the safest and most efficient type of pavement markers. There is no timetable for the study at this time but once it commences, we should have the results within a year.
But whatever the outcome, expect to bump up against them for a long time to come.