Traffic-Safety Issues: Cellphones or EMCs?

EMCs and traffic safety have concerned planners and communities. Recently, an EMC informed me about traffic construction, with a display hold time of approximately three seconds per message. If EMCs caused accidents, would these signs display public-safety messages?
Which is more of a hazard, an EMC, or cellphones, text messaging and other driver distractions?
A 2003 study by the National Highway Traffic Safety Administration indicated cellphone use while driving could be comparable to driving under the influence. Here’s the link for this study’s summary: www.autosafety.org/foia-reveals-cell-phone-studies.
In 2007, the Foundation for Virginia Tech Transportation Institute for Automotive Safety Research and Tantala Associates provided two studies. This research offers evidence that traffic accidents are no more likely to happen in the presence of digital billboards than in their absence. The crash-causation and statistical study was conducted by Tantala Associates, a consulting-engineering firm. Here is a link to an article that discusses both studies: www.mediapost.com/publications/?fa=Articles.showArticle&art_aid=104192
Although both studies concern digital billboards, their information provided is relevant for on-premise EMCs.
The April 2009 Wachtel Report examines traffic-safety issues with on-premise signs. This report will most likely surface and be cited as documentation that on-premise signs may create traffic-safety issues. It is important to note this report is making a supposition in relation to on-premise signs and traffic safety. A full copy of this report is available at this link: www.scenic.org/pdfs/NCHRP%20Digital%20Billboard%20Report.pdf