Pete (and Dan), when part of my responsibilities included the police fleet we had quite a number of squad cars hit from behind while they were on the shoulder of the road with their emergency lights flashing; both when we had only red lights and after we went to red and blue. So I did a bit of research and found that the California Highway Patrol, along with the National Institute of Standards, had done some pretty extensive studies. But I think, Pete, that you have your colors wrong. Intoxicated and/or tired drivers tended to home in on red lights, and ignore blue, but moved away from amber lights. It's believed, though not proven, that drivers are accustomed to almost instinctively following red lights, while normally recognizing amber lights as a cautionary indication, and more or less ignoring other colors. Of course this was long enough ago that blue lights on emergency vehicles were not all that common. At any rate, after we changed all our light bars on the tops of the cars to ones that had red, blue, and white to the front, and amber only to the rear, we never had another car hit from behind during my tenure with the department.