Bicycling, an observation

I've been riding in the mornings along Highway 61 for the last 6–8 weeks. The last week or so has been relatively foggy, so I've started turning on my flashing tail light (for those who care, it's a Planet Bike Superflash) before starting.

Some days the fog has turned out less dense than it appeared at first. On those days, I've noticed a scary pattern: The cars/trucks give me less clearance. That's right, they don't move over as much as when I'm not using the tail light. Now, that's not a big deal to me, because I'm riding on the generous shoulder, but it reinforce the findings that I posted way back in 2007 about helmet use. For those who don't click the link, motorists gave less clearance to cyclists wearing helmets than to those who didn't wear helmets! Counterintuitive, isn't it?

Here's my theory: Without a flashing light, the vehicles see a bicycle, but aren't exactly sure where it is on the rode, so they give you more clearance, just to be safe. With the flashing light, you are more visible to them, so they feel more confident that you have a enough room.

Now, I'm not going to stop using the Superflash on foggy days, but it does make you wonder...