I recall reading a story about a colony world in which there is a type of spice/seed that grows on the planet that is required for human life to continue. Control of this seed is used to control the colony world. There is a particularly long road between two regions of this world along which trade moves. The action focuses around the required spice/seed being stolen along that road. In fact, the title may even include the word 'road', but may not.
The story is older since I read it in the 80's. Any thoughts?