Ever notice those little squares cut into the curbs of old highways?

They’re seen on California roads built by the state from the late 1930s until at least the early 1950s and they were thought to help drivers see the curbs at night.

Were they some sort of Morse-code secret message? An alert to space aliens?

Turns out they were a well-researched attempt to make highways safer.

An article in the December 1937 California Highways and Public Works, retrieved from archive.org, goes into the research done on these small indentations created when the concrete was poured for the curb. They believed that just having the indentation was safer, as car headlights would pick up the shadows, with the driver noticing the tiny shadows. There were also plans to paint the inside of the squares with reflective paint.

“The best results for visibility of the curb under all driving conditions were obtained by making small recesses in the face of the conventional curb,” wrote F. J. Grumm, Engineer Surveys and Plans. “Curbs were constructed with different forms, widths, spacings and angles of recesses.”

By the time the big freeway building era began in San Diego in the mid-1950s, Caltrans had apparently abandoned the curb indents. And by the way, they’re also getting rid of Botts Dots, those lane-marker bumps we all love.

I’m sorry to say this has been a mystery to me for years. 30 years ago I worked at the City of San Diego with engineers of various sorts. I asked several of the old-timers about these odd boxes in the curbs and they couldn’t come up with an answer.

Well, now I know and so do you.


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