I've had the same problems with the speed-up, get-in-front and slow-down drivers as well as tailgaters as have the previous posters, but reading this thread brought a recent incident to mind.
I was driving home yesterday on a main street with 3 lanes going in my direction and stoplights every 4-8 blocks. In the right-hand lane and about 5 cars ahead of me was a dump truck and my first reaction when coming to a stop light was to maneuver to a lane that the truck wasn't in. That proved to be difficult, as about half of the other drivers in front of me had the same idea. Without even thinking of it, I had pre-judged the dump truck to be one of those slow vehicles that I didn't want to be caught behind. This same lane changing/avoidance process went on stop light after stop light with many of the drivers. The interesting thing here is that the dump truck was fairly new, clean, unloaded and faster than the front cars in the other 2 lanes. My bias against the dump truck was unfounded...I would have made faster progress staying behind it

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I suspect this same type of traffic flow bias exists against our smarts, just like any other vehicle we pre-judge as an obstacle to our progress whether it really is or not. I'm just as guilty of this as are the drivers who do this to me. It's just human nature.