This question may be completely flawed, but bear with me here. The original colonists were from England, and I ASSUME that the English used the left side of the road, like they do now.
I ALSO assume that the colonists got off the boat and used the left side of the roads in their settlements.
When and why did they swap? It seems like a lot of work, changing that for no real reason. Was it a slight at the British after the War of Independence or something? Even then, it seems a bit petty, changing the side of the road you walk/ride on to make a point.
My understanding may be entirely wrong here, if so I apologize.
Found what the other poster suggested would be in the FAQ:
Should help! :)
hmm, don't recall offhand whether the FAQ* will address your question head-on, but there is certainly lots of info about right/left driving here
Traffic * scroll down to the heading driving on the left or right
*see the link on the sidebar or the wiki tab
I never did get my doctorate, but I don't think that the colonists were driving a lot. Also, the automobile was essentially an "American invention," or "German," but regardless something which happened well after the 1780's. Even if there was a petty slight (and there probably wasn't as much as convention simply being picked up differently in the absence of international standardization) it was on the part of the British.
Think of driving in older cities, or older parts of cities, versus in areas developed after the car became a common mode of transportation. Then think about driving on a dirt road in the middle of nowhere. Today's massive road systems did not appear simultaneously with the invention of the automobile, much less did they predate it. Previous to this, using a road was a very different thing and motorized traffic developed differently in different contexts. There was at the time no need for 'everybody with a car' to all be driving on the same side. In this situation, habits would be free to arise differently, it's the same with language, dialects and other cultural conventions. An intentional slight doesn't seem to be either reasonable here or necessary for an explanation for the very common phenomenon of social differentiation in different geographical areas. At the same time, colonies still in British Imperial hands after the use of automobiles was widespread did tend to adopt the British system, and pre-motorized age French laws suggesting horse traffic and the like stay on the right were just as available to the Americans as the British preferences were.