Er, I meant Britons. Sorry. Brain fart.
Oddly, the Germans created the car, I think they get to decide which side of the road cars drive on. And the Americans created their mass production, so we get to decide which side of the road most of them are driven on.
I don't think there's a clear argument for which side of the road people should drive on, but if there is, it is that everything else is done on the right, probably because the right hand is primary in the majority of people. You need more dexterity for shifting than for steering, for example, so it makes more sense to sit on the left side of the car and shift with the right. If you're sitting there, you need to be sitting on the right side. And by the same token, since the left arm was the shield arm, that was the side on which you took your opponent when jousting. I've read around a bit on the subject of driving vs. walking, and in NZ they drive on the left and walk on the right. In England it's said they walk on the left, but there's a strict convention of standing on the right side of escalators coming out of the underground, which would better fit a walk-on-the-right model. It makes more sense to walk on the right since that's the arm you want to protect, and you'll do that with your left arm.
Bottom line, if it matters, it makes slightly more sense to drive on the right side. The opposite of the way the brits do it.