I was recently doing a long ride on my tandem which began very early in the morning. When the sun rose, we forgot to turn off our rear Niterider taillight. After riding for a few hours we noticed that the incidence of cars missing us by two inches when passing, cars coming up behind us and laying on their horns, and all the other dangers from cars that are part and parcel of normal day to day riding a bicycle in Miami had somehow stopped happening.
We started using our taillight during normal day time rides, and cars all of a sudden started giving us space, not honking at us etc. The effect was so pronounced that I started using a Niterider taillight also on my Litespeed during training rides.
So what exactly is going on here? My theory is that when drivers notice bicyclists at greater distances (which a bright light like the Niterider certainly engenders) they somehow find it less annoying that that bicyclist is on the road because the driver can make adjustments early enough to not need to slow down, hit the brakes, get stuck in the right lane until there's a gap for passing in the left lane etc.
The bottom line is that the stress, much of the danger, and a large part of the small annoyances while bicycling in even heavy urban traffic seem to go away when using a very bright flashing rear taillight during daytime riding. I doubt the effect would be the same with the vast majority of LED rear lights--the Niterider is probably 1000 percent brighter than a Vistalight or anything similar.
I don't have any commercial interest in Niterider, but given how well this has worked, I thought it worthwhile to let everyone here know about it.