One low and One high
The story I have heard was that the R&D folks found out that a motorcycle with 2 head lights on, that the auto drivers think it is a car far away and will pull out in front of you. I thought it was silly till I thought about the little old man might think just that. I do think that a Harley with head light and driving lights on, looks somewhat like a small sports car from afar. There are a lot of links here on that topic and maybe someone here can post a link or two.
Brent