Cheap land promotes sprawl. No land use controls allows the cheap land to be sold. People move out there and demand streets and traffic signals and wider streets, etc. This is the American way since day 1. It is the reason California is here.
Transportation allows sprawl.
Let me use a coffee mug analogy. Coffee mugs do not promote coffee drinking. Trying to wake up or to stay awake does. A coffee mug allows coffee drinking. If a high speed train connected Tracy to Silicon Valley and the land prices in Tracy were high or there were strong land use controls, development would be curtailed.