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Bridge-construction practices and reflective tape on semi-trailers

Mr. Alice:

Whenever I encounter bridge construction on the interstate, or most any other highways and roads, fastened onto the temporary supports at both sides of the road is a painted and illuminated, white board of significant size. What is it for? Since I’m imposing on your generosity, what’s with the inverted, L-shaped strips of reflective tape at the top rear corners of semi-trailers?

— Geezer, Escondido

I’ll overlook the fact that you’re double-dipping into the Alice Fountain of Knowledge on this one, Geezer, thus proving the depths of my so-called generosity. The white boards in question serve as a kind of light control. They prevent the construction site’s lighting from spilling out and causing glare, focusing it on the underside of the bridge where it’s most needed in the perpetual half-darkness of the highway overpass. This (rather brilliant) idea to use them came about after decades of motorists complaining to Caltrans about being blinded along the freeways.

As for the reflective strips on semis, they’re for taking digital height measurements at weigh stations and such. Retro-reflective materials (which you may recall from my column last week) are useful in measuring distances because lasers bounce off of them with uncanny precision. The Apollo astronauts actually left a battery of retro-reflective markers on the surface of the moon for use in calculating the distance between Earth and Moon with amazing accuracy. Compared to that, measuring the height of a tractor trailer is a piece of cake.

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Mr. Alice:

Whenever I encounter bridge construction on the interstate, or most any other highways and roads, fastened onto the temporary supports at both sides of the road is a painted and illuminated, white board of significant size. What is it for? Since I’m imposing on your generosity, what’s with the inverted, L-shaped strips of reflective tape at the top rear corners of semi-trailers?

— Geezer, Escondido

I’ll overlook the fact that you’re double-dipping into the Alice Fountain of Knowledge on this one, Geezer, thus proving the depths of my so-called generosity. The white boards in question serve as a kind of light control. They prevent the construction site’s lighting from spilling out and causing glare, focusing it on the underside of the bridge where it’s most needed in the perpetual half-darkness of the highway overpass. This (rather brilliant) idea to use them came about after decades of motorists complaining to Caltrans about being blinded along the freeways.

As for the reflective strips on semis, they’re for taking digital height measurements at weigh stations and such. Retro-reflective materials (which you may recall from my column last week) are useful in measuring distances because lasers bounce off of them with uncanny precision. The Apollo astronauts actually left a battery of retro-reflective markers on the surface of the moon for use in calculating the distance between Earth and Moon with amazing accuracy. Compared to that, measuring the height of a tractor trailer is a piece of cake.

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4S Ranch Allied Gardens Alpine Baja Balboa Park Bankers Hill Barrio Logan Bay Ho Bay Park Black Mountain Ranch Blossom Valley Bonita Bonsall Borrego Springs Boulevard Campo Cardiff-by-the-Sea Carlsbad Carmel Mountain Carmel Valley Chollas View Chula Vista City College City Heights Clairemont College Area Coronado CSU San Marcos Cuyamaca College Del Cerro Del Mar Descanso Downtown San Diego Eastlake East Village El Cajon Emerald Hills Encanto Encinitas Escondido Fallbrook Fletcher Hills Golden Hill Grant Hill Grantville Grossmont College Guatay Harbor Island Hillcrest Imperial Beach Imperial Valley Jacumba Jamacha-Lomita Jamul Julian Kearny Mesa Kensington La Jolla Lakeside La Mesa Lemon Grove Leucadia Liberty Station Lincoln Acres Lincoln Park Linda Vista Little Italy Logan Heights Mesa College Midway District MiraCosta College Miramar Miramar College Mira Mesa Mission Beach Mission Hills Mission Valley Mountain View Mount Hope Mount Laguna National City Nestor Normal Heights North Park Oak Park Ocean Beach Oceanside Old Town Otay Mesa Pacific Beach Pala Palomar College Palomar Mountain Paradise Hills Pauma Valley Pine Valley Point Loma Point Loma Nazarene Potrero Poway Rainbow Ramona Rancho Bernardo Rancho Penasquitos Rancho San Diego Rancho Santa Fe Rolando San Carlos San Marcos San Onofre Santa Ysabel Santee San Ysidro Scripps Ranch SDSU Serra Mesa Shelltown Shelter Island Sherman Heights Skyline Solana Beach Sorrento Valley Southcrest South Park Southwestern College Spring Valley Stockton Talmadge Temecula Tierrasanta Tijuana UCSD University City University Heights USD Valencia Park Valley Center Vista Warner Springs
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