My first thought is, did he have a flag (or two) for the trailer? The car right behind him would see the trailer already, but the cars behind that car benefit from seeing the flag and, generally, gain more awareness of what's going on near the cyclist.

Busy, but like Ka_Jun was figuring, was it slow?

That's why I still look both ways before crossing the street, even when I have the light. And, yes, look both ways before crossing a one-way street, too; I figure that if someone's going the wrong way, they're not thinking clearly, are getting confused, and are, therefore, more dangerous.

I heard a mother tell her little girl, "Yes, you can cross now, because the sign says you can." That really irked me. You can't know when a driver approaching the intersection isn't paying attention. All it took to total my first car was one such driver -- imagine if I was a pedestrian instead.