What if sections will be needed now, and it's easy enough to make a plan to eventually connect all of the parts as needed? Get the zoning work done to prevent

What if sections will be needed now, and it's easy enough to make a plan to eventually connect all of the parts as needed? Get the zoning work done to prevent anything over 2 stories tall being built over the planned route, and then build the various sections as needed/as budget is available. I'm not saying that's what happened, but I can see smart, modular, as-needed infrastructure projects being drawn out over decades like this.