There are currently about 400 digital signs across the country.
The technology has excited both billboard companies, which can generate three to five times more money from the digital signs, and advertisers.
While the billboard industry says the digital signs are not dangerous, driving safety researchers say there has not been enough research to know for sure.
Still, researchers said the digital signs may tax drivers' awareness more than old-fashioned static signs.
The federal government has also allotted $150,000 for a future study of digital signs.
By August 2009, digital signs were added to the garage to alert motorists as to how many spaces remain prior to entering the facility.
We followed a long corridor to the lobby, where a digital sign above the front desk reminded guests to keep visitor's passes properly displayed.
In the days after the destruction, the church's digital sign had the message "He'll be back" running.
At many airports and on the edges of some European cities, overhead digital signs display information about available spaces in parking decks.
Stations are announced on digital signs and in voice recordings.
