So here's a scenario. You're driving down a two-lane road. There aren't any lines on the road, but you know it's a two-lane road, because it's not wide. Cars are going by on the left. Motorcycles are going by between you and the cars on the left. But they're also going by on the right. And occasionally they'll pass from one side of your car to the other, often right in front of you. Sometimes motorcycles are coming at you in your lane. Sometimes other cars are coming at you in your lane - either because they're going around one of those pushcarts filled with coconuts, a carro publico or a truck has stopped on their side of the road and blocked traffic, or because they are tired of sitting in the long line of backed up traffic on their side of the road, and they've decided to simply go around the traffic. In your lane. But they'll squeeze back over to their own side when you drive up and stare at them. Sometimes that two-lane road becomes a three- or four-lane road, and everybody accepts that it's okay, because there's enough space for you to squeeze through between the cars on your left and the sidewalk or ditch on your right. And watch out for that giant pothole that reopens every time it rains.
Actually... You know what? I don't think I can adequately explain traffic in the DR. You'll just have to come visit and see for yourselves.