The growing number of digital billboards on U.S. roads and highways consume large amounts of energy and are creating a wide variety of electronic waste, according to a new report. The new study says the typical digital billboard consumes about 30 times as much energy as the average American household. The digital billboards use more efficient LED (Light Emitting Diode) lighting than traditional signs, but deploy so many of the LED bulbs on each billboard that energy use is high; traditional billboards use just one or two large bulbs to illuminate signs, according to the study (PDF) by Gregory Young, a Philadelphia-based architectural designer and urban planner.

In addition, digital billboards are illuminated day and night, and require cooling systems that use more energy. And while LEDs, plasma and LCD screens are recyclable, reuse is not mandated, leading to a large surplus of "techno-waste," said the study, published by the group Scenic America. The U.S. has roughly 800 digital billboards, compared with 450,000 traditional billboards. But use of the technology is expanding quickly, with more than 2,000 expected by 2012.