There is an adjustable bungee cord connecting the handlebar of the towed bike with its seat post. This way the front wheel can pivot, but it will always return to the straight line after turn is completed. Without this towed bike swings too much. There are also few tricks in suspension which make ride smooth even on a bumpy road. It took me quite a few trials and errors to figure all this out, i even patented the system, just in case
