0705ctt Driving signs_lo res


Next time you are driving in the rain, think about the engineering that ensures road signs and road markings are visible. Or just wear your sunglasses. Credit: 3M; You Tube.

Top image: New (left) and old highway signs in Canada. You might see it for yourself if you drive to MS&T in Montreal in October. Credit: Wikipedia.

Happy Independence Day weekend! Many of you are enjoying some R&R today and, in the time-honored tradition of the holiday weekend, may be enjoying a road trip with the family.

In fact, the American Automobile Association predicts (pdf) that about 40.8 million of you will be traveling at least 50 miles away from your home between July 3–7. (This is down a little from 2012’s estimated 41.1 million travelers, which AAA attributes to the holiday falling on a Wednesday last year, but still above the historical average of 38.9 million travelers.)

If your trip involves highways, you might want to take a moment to read this New York Times online article about the development of modern road signs. (Hat tip to Allstate’s blog, “From Rome to Detroit: A History of Street Signs.”) When your passengers start asking “are we there yet?” you can dodge the question with a history lesson on traffic control tossed with some materials science, instead.

You probably are aware that that back in the day, an engraved stone mile marker—a “milestone”— was state-of-the art, and it remained so for centuries. Nowadays, roadsigns are the result of sophisticated materials and optics science to make them reflective.  Encapsulated glass spheres provide the reflectivity for many of the road signs and road markings, but this 3M video also mentions ceramic reflector elements. The latest road sign products (pdf) from 3M feature a technology they call “diamond grade reflective sheeting,” which is based on “highly canted cube corner elements.” 3M claims that the new reflective sheeting product reflects 58 percent of the incident light to the driver, compared to 14 percent from encapsulated glass bead technology. I did not see a specific material mentioned in the patent (pdf) for the technology—I confess to only scanning it quickly—but the key seems to be that the reflector is cubic.  (That clue ought to provide a hundred miles or so of mind-cud.)

Of course, rain presents one of the challenging environments for road sign visibility. So, naturally, I was curious when a friend sent me a note that wearing sunglasses while driving through downpours could actually increase visibility. I had the “good fortune” of testing it out last week and convinced myself I could see a little better through the sunglasses, after I got over the eerie off-hour twilight effect.

But, friends, that was just my imagination! A little sunny-day research led me to snopes.com, the online mythbusting website. It turns out that wearing polarized sunglasses improves visibility when driving through the rain. According to the website, “Polarized sunglasses work to block horizontal components of scattered or reflected light, which means they help counteract the scattering of light that atmospheric effects like fog or rain have on daylight.”

“Non-polarized lenses won’t do anything other than make the field of vision darker, which means wearing them while driving in the rain would increase the hazard, not reduce it,” the website concludes, declaring the idea of wearing sunglasses in the rain “Partly True.”

I suppose that switching between regular glasses and non-polarized sunglasses in the interest of scientific inquiry was, well, not very bright!

By the way, for those of you who get jazzed by surveys and statistics, I was surprised by the level of sophistication of the yearly Independence Day AAA travel survey. The survey looks at a broad range of economic factors that affect travel, including “macroeconomic drivers such as employment; output; household net worth; asset prices including stock indices, interest rates, and housing market indicators; and variables related to travel and tourism, including prices of gasoline, airline travel, and hotel stays.”

Happy travels. Be safe. Wear sunglasses responsibly.