The route was lucrative, and fought over, wound up ruled by a succession of different conquerors who came and went, and all the time it was open, but the costs varied based on how many payoffs and to whom they had to be paid.
As a trade route, it was open for lapis lazuli, Indus Valley beadwork, obsidian, and a variety of other items going on back into prehistoric times. Chinese Silk wasn’t available until about 500 BC.
Frequently it was closed because the costs exceeded the value of the items transported.
Nomadic tribes are not always renowned for understanding the long-term financial benefits of imposing “taxes” instead of just killing the traders and taking ALL their stuff.