Rumbler rattles motorists alert Officer.com, Law Enforcement Technology magazine, April 2008

http://www.officer.com/print/Law-Enforcement-Technology/Rumbler-rattles-motorists-alert/1$41127
"Getting a driver's attention today can be nearly impossible. Loud music, cell phones, fans blowing and maybe even children bickering in the backseat distract today's drivers. With the Rumbler Intersection-Clearing System, Federal Signal makes the nearly impossible, possible."