Theory #2 - Left-lane exits and EZ Pass
Maryland is one of the few places where some of the exits for other roads are actually on the left side of the road. I'm not sure why some exits are like this. Most exits are on the right side. While the impact of left exits isn't always readily apparent, in the context of the current discussion it may be more obvious. For those who ignored all of the signs telling them the exit was on the left they make a dive across all lanes of traffic to get there (slowing down all lanes of traffic and not just the left one!) On the other hand, for those anticipating the exit they often hang out in the left lane until they get there. The end result is that the left lane quickly get congested.
But left-lane exits are not the only reason you may find people on the left side. EZ Pass, a system designed to make toll collection easier for drivers on the I-95 corridor, has lanes on the left sides of the toll plazas. While many EZ Pass drivers have signed up to make traveling through the toll plazas quicker, there are many who just don't want to dig in their pockets for loose change. As with the left-lane exiters, EZ Pass just adds another reason to be in the left lane.
Both of these factors help to explain the left-lane driving when you are either near a left exit or a toll plaza, but not when either of these are no where to be found. I would hazard a guess that those annoyed by the person driving in front of them without moving over would not be annoyed by these circumstances. After all, once arriving at the exit the person would no longer be in front of you, right?
While this theory has some tangible merit, there has to be more to it than that. Stay tuned for Theory #3, Cruise Control.