The New York Times covers the motorist distraction issue of digital billboards as part of its ongoing Driven to Distraction series.
Existing studies make it clear that digital signs are a distraction. As an exhaustive report conducted for the American Association of State and Highway Transportation Officials of prior studies concludes:
"Those [state and local officials] who think their job is to do what they can to enhance safety for the traveling public based upon the best available evidence now have, in our opinion, access to a strong and growing body of evidence, including evidence from industry funded research, that roadside digital advertising attract drivers' eyes away from the road for extended, demonstrably unsafe periods of time."
See more on digital distraction at Scenic America here.