Pink dots denote Philadelphia's current inventory of digital billboards (10 total) concentrated along I-95 and the Schuykill Expressway.Photo: Gregory Young

State and local governments have banned digital billboards for safety reasons, but no one's considered the technology's environmental ramifications.

And we should, says Scenic America, which works to preserve and enhance the aesthetics of communities and byways. Though touted as a greener alternative than traditionally illuminated billboards, the nonprofit organization's detailed analysis of how LED-illuminated billboards work shows they use much more electricity than regular billboards. A 14x48-foot LED billboard in Florida uses 162,902 kilowatts annually, 23 times the energy required by the same size billboard with four halide lamps.

That's because digital signs use thousands of 2- to 10-watt diodes that operate around the clock rather than just at night, and the controller that rotates the changeable images must be air-conditioned to avert heat damage.

Alaska, Hawaii, Maine, Michigan, Minnesota, Montana, Rhode Island, and Vermont have banned or are considering moratoriums on digital billboards, as have at least 23 cities and counties in Arizona, California, Colorado, Florida, Georgia, Minnesota, Missouri, North Carolina, Tennessee, and Texas.

Most U.S. zoning ordinances regulating the signs are woefully inadequate. In Europe, in addition to brightness and “dwell time” (how long each advertisement in a multiple-message rotation is displayed), regulations address:

  • Traffic speed on the adjacent roadway
  • Type of street or interchange
  • Proximity of traffic control devices and whether a message could be mistaken for such a device
  • The amount of information communicated and legibility
  • Legend height
  • Potential to obstruct a driver's key sightlines.
  • Advertising companies get around prohibitions regarding characteristics like animation, rotation, scrolling, flashing, or color changes by describing the signs as “static.” The report recommends language that includes any and all digital signage, defined as “any sign capable of displaying words, symbols, figures, or images that can be electronically or mechanically changed by remote or automatic means.”

    The Outdoor Advertising Association of America estimates there are 800 digital billboards nationwide, and expects several hundred to be added every year.